Technical MB General

Technical non-specific MB

Sprinter >2006 Cutting out and None Start – A Few Notes – Causes and Things to Check

 

Sprinters up to model year 2006 share some similarity with the later model when it comes to ‘mysterious’ cutting-out and repeated intermittent non-start issues, this article covers specifically the earlier 4 cylinder Sprinter >2006, although some of the items covered are also common to the later model. The points covered here are some common failures and do not represent an exhaustive list of issues that may be causing problems with your vehicle. You may find at least some clues that help towards your own fault finding from the information given below.

To start a Mercedes CDI diesel engine, there must be a set of conditions met that the ECU requires to initiate running the engine.

Fuel

The fuel rail must provide an absolute minimum cranking pressure of between 250 and 300 Bar, any less and the ECU will not allow the engine to start. Causes for this pressure not to be maintained could be due to internally leaking injectors, faulty fuel pressure regulator or its O-ring seal (see covering article here), faulty rail pressure sensor, High or Low pressure fuel delivery pumps. Equally any air resident in the fuel delivery system will hamper starting. Usually the seals used to terminate the clear plastic pipes from the low pressure to high pressure pump give rise to air bubbles visible in these pipes, which is not a good sign and will need to be further investigated. It is worth noting that unlike any circulating diesel feed system, the fuel exiting the high pressure pump is not self bleeding and any air held within the rail will take some time to clear should you open the system to atmosphere (for instance if you do a poor job of pre-filling a new fuel filter at service).

Sprinter >2006 Cutting out and None Start 1

It is worthy of note that the diesel pressures within the system of a running engine could be in excess of 1,600 Bar that is very capable of doing you some damage! – always use caution when inspecting and working on running CDI fuel systems.

Should at any point the measured pressure drop within the fuel rail, say if there were a serious ‘high-side’ leak or if you were to open a feed union to an injector the ECU would instantly cut the fuel delivery and shut down the engine as protection. Equally there is overpressure protection for the fuel system, where if it ever rises beyond a predetermined ‘safe limit’ the ECU operates the shut off valve on one of the three piston element heads of the HP diesel pump thus dramatically reducing delivered pressure to a safe level. This shut off device is the large tower like solenoid that extends from one element (there are three) of the high pressure pump, it has a two pin electrical connection and loom plug at its end.

Sprinter >2006 Cutting out and None Start 2

‘Live data’ is the best way of determining fuel system pressures and the operation of the engines attached control devices, but obviously in a running engine. You will have to inspect the fuel system of a dead non-start engine using the functional details above as a guide. Unless you have a major fuel leak or the delivery pumps have catastrophically failed, fuel related problems are not often sudden and tend to show themselves as intermittent transient problems for a period of time before they get to the stage where the vehicle will no longer start. More often non-start problems arise from the electrical system.

A really useful link on the Sprinter fuel injection system here

Electrical

For the most part the electrical system will be the major cause of any none or poor starting issue. There are two main timing sensors fitted to the engine: Crank Position Sensor and Camshaft Position Sensor.  These relay engine positional information to the ECU so that it can determine when to accurately fire the injectors so that the engine can run.  Any synchronisation errors that occur between these two primary angle measuring devices will cause an engine to slip into limp home if running, and if stopped, the engine will not restart until it gets valid signals from both.  The cam position sensor is mounted on the top rear of the valve cover slightly to the left of cylinder 4 (rearmost looking in) and gets its positional signal from a lobe on the cam. Due to its location directly above the exhaust manifold, it is subjected to regular extremes of heat and daily cycles of hot and cold.  It is not uncommon for this sensor to exhibit thermal problems, where a cold engine will start and run fine, then once warm, would falter or not restart until cool. Replacement of this sensor is quite cheap – sub £30, and even if it does not cure any problems you may have, it is best to ‘eliminate it from enquiries’ if there are any synchronisation errors recorded.

The crank sensor lives on the block seam of the engine and gearbox bell housing, just above the starter motor, it picks up its pulses from teeth on the flywheel. Generally it is quite reliable – if you have problems starting the vehicle it is often a good quick check to watch the tacho needle flick slightly as you crank the engine. If it flicks, then this is normally a sign of an impulse from the sensor reaching the ECU. If however the tacho needle does not flick on spinning the engine over, then suspect crank position sensor problems.  It is possible this sensor can suffer from thermal problems but not as frequently seen as with the cam sensor.

The connecors and cabling to the injectors are important things to check, if any connector to any single injector becomes disconnected, then the engine will not run, equally if one injector solenoid becomes disconnected when the engine is running the engine will die.  It is a known problem for the injector wiring loom that lies under the black plastic cable tray beneath the fuel rail to have issues whereby the injector cables rub and abrade against the metal surface of the alloy rocker cover over time. Once the cable insulation weakens and any of the conductors short to ground, it has a similar effect to disconnecting an injector – the engine will stop. You can cut strips of plastic bottle and slide them under the cable tray to insulate the cable from the alloy cover to test if you suspect this is an issue.

Sprinter >2006 Cutting out and None Start 3

The injector solenoid wiring can be easily checked for continuity and insulation to ground by removing the injector connectors and metering out the wires directly to the ECU under the dash.  The injectors connections are the large gauge wires on the push in connector to the far right looking at the ECU under the dash.  Release the ECU retaining springs to drop it down into the passenger footwell to make it easier to work on.

If you detect anything untoward with the wiring during your continuity checks, the first obviously place to look for broken cables and damage is to cut open the outer insulation on the section of loom that drops from the engine, over the left engine mount on its way to the rear of the battery shelf area. Here you will find the most mechanically vulnerable selection of sensor and engine management cables – be sure to check here first. Note: although not related directly to non starting, as previously mentioned in other posts, the turbo control, vacuum solenoid valve loom, hooks round the front of the radiator from behind the passenger headlamp and travels across the front crossmember. It passes the horn onward to the vac valve situated under the air box. Commonly this loom is found to be damaged or broken in the area where it snakes past the headlamp tinwork on the front panel. See here for more related fault finding detail.

If all fuses prove good, and the engine cranks but will not fire, then take a look at the ECU connectors. Remove each of the plugs and check that water, usually from a poor windscreen seal or rust-rotten screen surround, finds its way onto the ECU.  Over time the fine connectors and pins start to corrode and all manner or electrical issues ensue.  To remove the ECU plugs with lever tabs, push in the small locking pip just behind the upright grey lever, on the black part of the shell. Then bring the grey lever down over it and continue to move the lever to the horizontal in an arc, this will eject the connector from the multiplug.

Sprinter >2006 Cutting out and None Start 4

I have had instances where intermittent cutting out has been due to dry joints on the PCB inside the ECU alloy box.  To check this out – once all the cables have been removed undo the six torx head screws holding the cover plate onto the pressed aluminium ECU box. Once removed, lift off the plate and remove the PCB assembly from the pressed case.  You can now inspect each pin solder joint with a magnifying glass to look for a broken or poorly soldered/corroded joints.  Often careful re-soldering of the suspect joint will provide a suitable repair, obviously if its corroded rather badly, the chances are that the multilayer board is damaged and at worst a replacement ECU could be needed (very rare).

Sprinter >2006 Cutting out and None Start 5

If you ever get any code reader messages relating to ‘capacitor voltage low’ (Autel or none-Star diagnostic tools) I have always found these to be a good indication of faults connected to the CPS, and after replacement or repair to its connecting wiring, it has always fixed the problem which was originally accompanied by an engine that will just cease running for no apparent reason. My first advice would be when the only recovered code is one relating to ‘capacitor low’ then more often than not – its related to the CPS and well worth a try first!

Sprinter >2006 Cutting out and None Start 6

Notice the relay on the right has a ‘pushed-in’ terminal

If the starter does not crank at all, then it is good to understand that the start command is issued by the ECU and not the key!  This is because the ECU monitors the key security module and will disallow starting unless a valid key (with correct internal chip) is being used in the ignition switch.  Any problem that displays ‘KEY ERROR’ in the dash LCD module is connected to using an incorrect key, a broken or missing key code chip, or a problem with the key reader detection coil (around the ignition switch) or the key security module itself (SKREEM).  If the key signal is valid the start signal will be actioned by the ECU. In auto versions it will also look to see if the transmission is in neutral or park.  Once an ECU start output is active, the start relay is commanded.  It lives beneath the driver seat, accessed through the flip off side panel, once caused to pull in – this puts voltage onto the coil of the starter motor, via a black with yellow tracer wire in the loom.

Sprinter >2006 Cutting out and None Start 7

more clearly – the pushed in relay contact

I have seen odd instances where because of the nature of the size of the relay spades, they ‘give-way’ when pushed into the fuse board receptacle, pushing them up inside the relay case – misaligning the internal switch contact faces. Often a root cause of intermittent starting/cranking with just a ‘click’ – should obviously the battery and starter cabling prove to be in good order.  The dead giveaway here is if the headlamps stay bright and hardly dip when an attempt to crank is made, if it is not the relay and good voltage is reaching the stud terminal on the starter solenoid, then the chances are the solenoid itself is faulty and the starter would need replacement.

Sprinter >2006 Cutting out and None Start 8

Inside the relay – the silver plated contacts are pushed out of alignment making for poor or high resistance switching

You can of course quickly test the starter by ensuring the vehicle is out of gear and then shorting the large 13mm power stud/nut on the starter to the smaller 10mm nut on the solenoid with a robust old spanner or jump lead clip. If the starter is healthy, then the motor should crank. If not, then you are most probably looking at a faulty starter motor.  If it does crank, and will not turn over from the key, then you will have to investigate why following the information in the above text.

Sprinter >2006 Cutting out and None Start 9

I hope the above gives you a little information to help you fault find a few little known anomalies with the Sprinter and hopefully it leads to identifying  your starting issues.

 

 

 

 

Mercedes C180 C200 Kompressor – Cam Chain – M271 Death Rattle

 

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Well I had read a great deal over the years about major engine problems with the M271 four cylinder petrol engine that had taken over from the slightly older M111 unit.  For me it had been just something you read about, until last week when the wife’s C200K (2004) slipped a number of teeth on the cam gear and destroyed itself while attempting a start in the drive at home.

This car had covered 80k miles always been regularly serviced at the correct intervals and to be honest is a cosseted example of the marque!  Even so it fails to escape failure of the M271’s achilles heel – the timing gear.

Taking the call from work I new instantly what the issue was and it was only confirmed when arriving home.  I coupled up the code reader and sure enough after a read, there were several cam synchronisation errors, only possible if things were not dancing in tune.

Mercedes M271 Cam Chain Problem 2

Removing the valve cover revealed what I knew was true, moving the flywheel to TDC showed the Inlet cam to be over 30 degrees advanced and the exhaust to be 20 degrees retarded, wow thats done damage!

A quick compression test showed zero compression on any cylinder so we had to put this right.

In many cases where this happens and perhaps the car is not the most shining example of the model, the repair cost is many times that of the value of the vehicle and the owner decides to scrap the vehicle or sell it on ‘spares or repair’.  In this case, where the vehicle is a trusted family car in very nice condition, just MOT’d with a good body and leather, I could not imagine sending it to big scrap heap in the sky – it was going to be fixed!

Mercedes M271 Cam Chain Problem 3

Tearing down the engine and placing all the parts in the boot as I went was the first call to action, not only did I want to see the extent of the valve damage but also the degree to which the pistons may have been damaged.

Once the cam gear was removed and manifolds disconnected, the head could be lifted to reveal what lay beneath. Thankfully this operation revealed a set of undamaged pistons, with just the slightest indentations where they had met the inlet valves, nothing to worry about there as the exhaust valve-train looked totally undamaged. So good to go!

Mercedes M271 Cam Chain Problem 4

I spent a couple of days researching new parts prices and with a mix of Ebay and Euro Car parts sources all I required for the rebuild for a fantastic £220 inc vat!  The two VANOS (variable timing) cam gears were suprisingly not showing any more signs of wear that would be expected for the mileage and close inspection showed little wear either to the profile or contact points where the drive is transmitted to the dog from the chain.  If these cogs were damaged or worn the replacement cost for these components alone would be £500. (www.M271.com is among a few others the UK source for these two gear components should you need them).

The list of parts I purchased was as follows:

Febi Cam Chain and Tensioner Kit inc Guides and Tensioner Bung

Timing Chain – Extra link

8x Inlet Valves for Intervalve (Euro Car parts)

16 Valve stem seals

Valve Grinding Paste and Stick

Reinz silicone gasket sealer

Elring Head Gasket

Cylinder Head Bolt Set

Vaico 3 Pipe Breather pipe set and non-return valve (located under supercharger – more on this later!)

2 litres of Antifreeze

2x Rubber bungs for timing chain guide pins/cylinder head

1x 2.5 diameter inch Jubilee Clip to replace the ‘spring type’ one mounted on the rear of the air box/MAF pipe

1x Big bag of ‘Good Luck’

Once all the parts had arrived I removed the old valves from the cylinder head and ground in the new replacements, fitting the new valve stem seals as I went. After a tedious time cleaning off the sealant debris from all mating gasket surfaces it was finished ready to fit.

The block was now going to have the post mortem, as I felt only the chain had stretched and caused this issue because it was no longer able to held in good tension by the hydraulic plunger-type tensioner. Removing the alternator revealed a large bung that gave access to the cam chain tensioner inside the timing cover, once removed the tensioner within simply unscrews out with a 17mm socket (40Nm when it goes back in).  In combination with the removal of the right hand chain guide, enough timing chain can be hauled out of the timing cover to safely split a link and attach the new chain to the end of the old one and wind it through.  I measured the new chain on a hanging flat surface and comparatively measured it against the old one when it was removed. The old chain had stretched about 12mm – which equates to adding an extra link to the timing chain.  This would have resulted in a mechanical 20 degree retarded valve set over TDC.  Once elongated to this extent the snatch of the chain in each cycle works the links of the simplex chain doubly hard and the wear simply accelerates.

Mercedes M271 Cam Chain Problem 5

As a quick check on an engine that has not yet failed, is if you lift the valve cover and set the crank to TDC, you should see the timing marks on the cams-to-carrier align perfectly for a good timing chain, a worn cam chain or gears will exhibit a misalignment in these marks, namely rotating the crank beyond TDC to align the retarded inlet cam, that when aligned with its index will further show a trailing exhaust cam by about one tooth!  REPLACE IT QUICK!

The tensioner on my engine had almost extended to the end of the piston, at this point because of the level of extension, hardly any spring pressure was being transferred to the tensioner guide – meaning in a start-up scenario, where low oil pressure would be ‘building’ in the tensioner it would rely pretty much on only the spring to cover the interim time until oil pressure begins to holds things in place.  This without doubt is why the majority of failures happen on starting the engine and very rarely when running to road speed.

Mercedes in their wisdom, tried to patch the issue by adding a small non-return valve to a modified tensioner saddle mount, the idea of this was to control oil seeping back from the tensioner during periods of standing, assisting the pressure ‘build up’ speed from a start.  It didn’t seem to help the widespread failure issue, just made the engine quieter until it had turned over a few times on start up.  It I think was really more a case of the chain wearing beyond the limits of adjustment at the tensioner mechanism, whereby after which its only a matter of time until disaster strikes.

Once the timing chain has been fitted and head replaced the timing can be set perfectly to align with all three marks, confirming all is well. Screwing in the tensioner fully, having secured the guides with their pins, the engine can be turned with a socket on the crank nut to prove your work.

Mercedes M271 Cam Chain Problem 6

A screwdriver confirms absolute TDC inserted through the plug hole of the frontmost No.1 cylinder.  It has been known for the harmonic balancer rubber to delaminate on the crank pulley – shifting/pulling the market TCD position round to an arbitrary point on the circumference as the faulty pieces slip round each other.  Obviously this needs to be replaced too if found to be faulty, don’t ever take the factory TDC marking for granted, check and confirm everything is truly relative to No.1 cylinder/piston position.

Build up is a slow process, the job start to finish including the head work is in the order of 20hrs hard labour.

There is one detail to tackle before the rebuild, certainly before the inlet manifold is replaced, and that is to replace the three small rubber breather pipes and non-return valve to one side of the supercharger (Kompressor).  These pipes form a valuable part of the crank case/vacuum system and because of their location, heat plays a large part in their failure. Once they become aged they perish and split allowing an imbalance in the sealed crank case to inlet system.  It has been challenged that even the slightest leak in these pipes can cause extra stress on the electronic VANOS Variator sprockets constantly trying to compensate for variance in induction air, adding to the impromptu wearing of the valve train mechanism and chain.  I have no proof that this is the case, but it sounds most feasible – see here.

Sure enough the upper of the three pipe set was split, so all pipes replaced before the rebuild of covering components took place. Common sense says replace these as a matter of course whilst visible, as they are placed deep under the inlet manifold and supercharger body, never to see the light of day.

Vent Hose: A 271 018 12 82
The 2 hoses below the Kompressor.
Hose: A 271 018 15 82
Check Valve: A 271 018 03 29
Hose: A 271 018 14 82

Eventually the job was completed, key turned with trepidation, but bursting into life and a running engine resulted, actually sounding far better than it had for a few years!

I have not bothered in this case to write a step-by step account of the above job, only you will know if you are competent enough to tackle it!  If you are, it is not overly complex, just a very, very time consuming job to do right – I am sure if you do decide to jump in, then you will manage admirably, calling on a set of skills built up over a few years of ‘playing engines’ to this level – its not for the faint hearted!

For the most, to rely on garages, dealers or independents to do this work for you would likely result in a very big bill indeed and it is easy to see why some folk just ‘put it all down to experience’ and scrap the car, never to buy Mercedes again – you can’t really blame them – M271 engine – bit of a lemon by all accounts!

 

Mercedes S500 (W220) and others – ‘Fly-by-wire’ throttle pedal fault

 

There had been occasion when I would decelerate to an intersection or junction and the engine would not settle to an even idle and remain rather ‘lumpy’. By tapping the pedal only slightly to raise the RPM’s by only the smallest amount resulted in the engine dropping back to its normal smooth idle.  It was also noticed that when pulling away from a junction the accelerator pedal occasion required more travel to get the car moving than it normally would, and when it did begin to pick up speed it moved perhaps more swiftly than intended.  There were no reported engine codes and also nothing illuminated on the dash to indicate a problem.

Asking around, a faulty throttle pedal position sensor was the confirmed as the most likely cause and the consensus of opinion was that they rarely ever caused a fault code to be registered, in fact one of my best contacts in the trade said that this condition directly pointed to the pedal issue, doubly confirmed by the fact that no code was reported.

Mercedes Electronic Throttle Pedal Problem 1

So I purchased a used part from a local breaker for £35 and fitted it in less than quarter of an hour from start to finish.

All that is involved is to remove the floor mats if fitted to gain unhindered access to the accelerator pedal.  In the rear moulding there is a plastic circular bung about half way up the assembly, using a small screwdriver or pick lever this out.  Beneath lies a recessed 10mm nut and washer, undo this with a small socket and extension.  Now grasp the pedal and lift it upward from the bottom, levering it outwards slightly to clear the fixing stud, once clear, pull down to disconnect the pedal assembly from its top locator.  The pedal will now be free, retained only by two wiring/loom connectors.

Disconnect the upper multiway plug to the position sensor model and remove the smaller two pin connector from the ‘kick-down’ switch from behind the pedal.  Note how the kick-down wire is threaded along the side of the pedal assembly and remove it.  The pedal can now be replaced with the new unit, threading the thinner loom back in its correct position and then connecting both wiring connectors back onto their respective plugs.

Feed in the pedal assembly, upper section first. Once located correctly, swing down the pedal to mate with the fixed mounting stud and replace the fixing.  Job done, all you then need to do is replace your mats and test the vehicle.

Mercedes Electronic Throttle Pedal Problem 2

On the S500 (W220) there were two types of pedal assembly used, one with a part number A220 300 01 04 for the post face-lift version circa 2004 onward and  part number A220 300 00 40 for the earlier model ranges to this point. Its a good idea to remove your own pedal, as it is such a simple task, to check the part number of the item fitted before searching for a spare.  A new non Mercedes replacement should cost in the order of £150.00 and a genuine part closer to double that.  A good used item should be in the range £35-£70 – the choice is yours!

Throttle pedal fault Mercedes Benz 1

Interestingly there is a large number of people who still believe there is a potentiometer within the pedal assembly, this is of course not the case and the often read advice to spray switch cleaner on or around the sensor is largely futile.  I have taken (broken) this unit apart so that you can see inside and confirm that in this case and most of the Mercedes models from about year 2000 on, this pedal assembly is all solid state and non serviceable.

Throttle pedal fault Mercedes Benz 2 Throttle pedal fault Mercedes Benz 3

What you can see within the housing is a pair of hall effect semiconductors mounted to a PCB. Each sensor is fixed within a static soft iron slotted core and as the pedal is rotated a small annular magnet rotates about this core.  Minute changes in magnetic field are detected by each of these two ‘Hall Effect’ sensors (compared electrical outputs from both sensors are checked for integrity, before a plausible position signal is accepted by the ECU as a failsafe, much in the same way as there is mechanical failsafe protection built into the pedal assembly by having two individual springs controlling the pedal return, just in case one breaks, allowing the pedal to return to a safe ‘throttle closed’ position rather than simply falling to the floor in a ‘full on’ scenario – Which would be a grand ‘brown trouser’ moment.)

Throttle pedal fault Mercedes Benz 4

Each degree of throttle pedal rotation at the rotating hinge point, relates to a predetermined magnetic field strength and this is interpreted as positional data referenced back to the ECU.

Throttle pedal fault Mercedes Benz 6

So, not a carbon track of a potentiometer to break or wear out, just electronics.  Obviously failures occur but in general this is a far more reliable, if slightly more complex solution to throttle pedal position sensing.  I would imagine the most common problem with failure of these pedal assemblies is the ageing of the semiconductor devices, once one device gives a slightly different output at any stage of its sweep, this is interpreted by the ECU as a mismatched signal and it will be ignored – hence dead pedal!  Once the signals are again in unison the throttle position is relayed and off you go…

Mercedes Sprinter 2007-on and VW Crafter Coolant Level Warning Problem

 

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The later Mercedes Sprinter and Volkswagen Crafter (and probably many others) uses a round plastic header/expansion tank in the coolant system.  This nylon spherical tank houses a rather clever float level switch that not only indicates a ‘low fluid level’ but also will illuminate the warning lamp in the dash binnacle if the ‘specific gravity’ of the coolant is less than specified – indicating to the driver that all is not too well with the coolant circuit.

Mercedes Sprinter Coolant Level Sensor Problem 4

On one of the fleet Crafter vans the coolant level warning lamp had come on and the driver had reported the fact.  When I investigated the issue there was no warning light on the dash, water level was fine but it could be clearly seen that the float inside the header tank had broken up, the plastic becoming somehow brittle and breaking away from its vertical retaining slide/guide. The internal float section is not available as a separate part so a ‘used’ second hand bottle was purchased.  After disconnecting the electrical connector at the base of the sphere, it is possible using a couple of sets of brake hose clamps to remove all the rubber hoses from the bottle in situ.  Once the single torx screw has been removed from the bottle mounting foot, orientating the bottle directly down into the void beside the engine, the connected hose-work can be removed quite easily and the bottle withdrawn upward without losing almost any coolant.  What coolant remains in the expansion tank can then be decanted back into the new bottle once fitted and piped.

Mercedes Sprinter Coolant Level Sensor Problem 3

On closer inspection once the bottle was removed, it could be seen that although the float inside the expansion tank was in this case the obvious problem (the actuating magnet it transpired, had been removed from the loose float by the driver, to turn off the lamp – why do they do that!)  Further dismantling of the float switch and level sensor revealed exactly how it functioned and also highlighted a further weaknesses that could in some cases cause issue with level measurement and warning lamp activation.

Mercedes Sprinter Coolant Level Sensor Problem 5

In the base of the tank is a moulded central vertical column that forms an upright guide that the tubular float moves on. The float rides up and down this central guide tube. Beneath and fitting into this tube is the sensor device. Although moulded in a plastic holder, this sensor is actually houses a small glass tube type reed switch that is triggered by the passing float (and magnet). The contacts of the reed switch close as the float magnet descends past a predetermined point and the warning lamp is activated. As the float rises above the reed switch, the magnet no longer causes the contacts to close and they spring open, resulting in extinguishing the coolant warning lamp.  There is a small resistor across the contact terminals of the sensor (around 800 ohms – the one I measured) This I am certain enables the ECU to detect in addition to reporting the coolant level status, a disconnected plug to the sensor, as it would have four possible measured electrical ‘states’ present between the sensor terminals as measured from the ECU. (1): Reed switch contact open, 800ohms = Correct fluid level. (2): Reed switch contact closed, short = Low fluid level or weak antifreeze water mix, Warning lamp lit. (3): Open circuit = Connecting cable disconnected or cut, warning lamp lit. (4) Cable shorted together = Connecting cable linked or fused together, warning lamp lit.

Mercedes Sprinter Coolant Level Sensor Problem 1

It can be seen from further ‘distructive’ disassembly the level sensor that it is susceptible to corrosion around the resistor and wire junctions, obviously due to the service environment it which it lives.  This discovery is important as if the float inside the water tank looks in good order, it may just be that the level sensor is faulty.  Depending on how keen you are with your fault finding, you could just slot a 1k resistor across the sensor plug and see if the warning lamp extinguished.  If it does, the chances are the sensor is faulty and can simply be rotated through 90 degrees and removed from the bottle base without any draining down or tank removal. Slotting in a working sensor, turning and reconnecting its plug to fit the replacement part.

Hopefully by exploring a little deeper how the float level switch works gives you a better understanding should you ever needed to trouble shoot the circuit.  The coolant level warning lamp is extinguished on the dash as you can see below, however you may notice the engine management lamp illuminated just behind the speedo needle hub – this is due to a faulty glow-plug and is next on the list for repair!

Mercedes Sprinter Coolant Level Sensor Problem 7

 

Skipping Mercedes 6 Disc CD Changer – Work-around Fix

 

The older type of CD Changers fitted to vehicles that are ten to fifteen years young, if still in situ, are running on borrowed time. Complex electromechanical systems and solid state LASERs don’t have an infinite life and often replacing the unit with a more modern radio/cd or MP3 player is the best choice.  However for those of us with older integrated COMAND systems that use a dedicated cut out in the dash, it is not always practical to change the head unit to a more modern type without huge expense and if we want to play CDs the remote changer has to work as the slot up front is for the NAV disc only.

Mercedes Benz CD Changer Repair Work-around 8

So what do we do then…  The option is to source a used unit from a scrap car or breaker but it is most probably from the same era and will most likely be well on its way to end of life.  So if you have an issue of ‘Magazine Empty’ or a badly skipping CD changer then there is a couple of last things to try before lifting the lid on the recycling bin and dropping it in!

As the LASER ages it becomes less powerful, rather like a halogen bulb that yellows and gives off a degraded level of illumination to that it did when new.  What we can do is increase the current to the laser slightly to lift its light output to compensate for its ageing and hopefully put the player back into service for a while longer. (please note that by increasing the LASER current over the specified factory set optimum, will have the effect of shortening its life, but my view is – if the player does not work correctly now because of a poorly performing aged LASER reader, then it clearly can only really be fixed by replacing it – a cost option that usually outweighs the purchase of a complete replacement player.)

Mercedes Benz CD Changer Repair Work-around 7

Obviously it goes without saying that it may just be dirt that is hampering the function of the CD player and in a few cases cleaning of the LASER lens will rectify the problem. This is the thing to try first before making any electrical adjustment. You can use one of the specialist cleaning CDs you can buy with a fine brush attached to the playing surface.  As this is drawn into the disc changer and played, the fine brushes gently sweep dirt and dust particles from the lens at very high speed.  More stubborn dirt will have to be removed with the delicate use of a cotton bud and surgical alcohol.

Mercedes Benz CD Changer Repair Work-around 6

Assuming that you wish to proceed with trying to breathe a new lease of life into your old disc changer, and that you are not too bothered by the chance of failure – then read on.

Eject the CD cartridge from the mechanism, disconnect the cables and orange DB2 fibre connection removing the player from its bracket in the car.  Working on a table or bench, unscrew the four cross-head screws from the sides and three from the back of the unit case, two of these hold the fibre convertor.  This then slots off sideways and the orange ribbon can be disconnected from the PCB connector by simply sliding out the white plastic anchor section about 2mm, releasing the foil from the PCB.  Now completely lift off the cover.

Mercedes Benz CD Changer Repair Work-around 5

Unhook the spring loading mechanism from each side of the unit, noting the position of the levers before doing so. These are set depending on your player installation – either Horizontal or Vertical.  Now pull off the four ‘gel’ shock dampers from the retaining spikes on the inner chassis (2 on each side) and undo a single retaining philips screw on the connecting orange foil assembly.  The inner chassis should now pull free from the base section.

Mercedes Benz CD Changer Repair Work-around 3

Identify the laser saddle and turn the lead-screw cogs with your finger to drive the LASER to the outer edge of the chassis, once in position turn over the player and you should be able to see the floating lens assembly through a gap in the mechanism top plate, there is enough room here to slide in a cotton bud and lightly brush the lens clean.  Use alcohol if any deposits are stubborn or difficult to remove, dry thoroughly and polish off any residue lightly with a dry cotton bud.  You may wish to try the player to gauge any improvement at this point, before moving on to the ‘last stand’ of adjusting the LASER current to get that last bit of life out of the player.

Mercedes Benz CD Changer Repair Work-around 2

Go back to the lead-screw and run the LASER to its most inward position in the chassis and then look on the revealed vertical edge of the saddle and you should see a small ceramic trimmer or potentiometer, about 3 mm in diameter.  This adjusts the LASER current. On Older wired and DB2 Mercedes and BMW, Alpine and Becker changers – current is increased by rotating this tiny trimmer anti-clockwise.  It only needs to be moved by a small amount, as a small increment is often all that is needed to restore the player to a working state that may last for a good period of time, maybe year or even more depending on your luck!  Remember the LASER is probably problematic anyway due to its age, so by increasing the current you are stressing it beyond its designed limits – but if you win a year or more use out of it before the inevitable replacement of the changer – whats to lose!  Rotate the trimmer about 30 degrees anticlockwise and rebuild the unit and test.  More often than not this is all that is needed to get things running again.

Mercedes Benz CD Changer Repair Work-around 1

If you need to apply power to the CD changer while on the bench, dismantle the fibre converter housing and attach 12v DC supply as shown across the power diode on the PCB

Good luck! Remember this is not a repair, it is hopefully a ‘get-out-of-jail card’ used to squeeze the possibility of a little more operating time from a unit that is eventually going to fail.  Usual disclaimers apply, you do this modification totally at your own risk under the full understanding that it may not work for you and that it could backfire and you end up junking your classic player.