Technical Sprinter

Technical Sprinter

Mercedes Sprinter and VW Crafter Side Loading Door – Cable Woes

Cable tray breakage – repair

One of the fleet Crafters pulled into the yard and the driver shouted in best Anglo-saxon that there was an issue with the side loading door and that there was a load of ‘wires’ hanging! On carefully opening the side loading door and beginning to slide it back on its runners all became apparent. The flexible cable tray (chain-tray) was in several pieces and the electrical cable it was supposed to house draping down dangerously in the area of the bottom door guide track.
Mercedes Sprinter VW Crafter Side loading Door Cable Management Issues 1
Most of the plastic chain-tray looked to be just unclipped from itself and would reattach to make a continuous ‘chain’ again, however there was one or two link sections that were broken, including the last one in the snake that connected directly to the lower stay of the bottom door roller. This lower stay-section has a plastic snap-in moulding beneath, this routes the bowden control cable from the handle mechanism to the runner latch operating a release for the sliding door when it is fully locked open.

Mercedes Sprinter VW Crafter Side loading Door Cable Management Issues 2

The only way to repair and re-route the cable correctly within the chain tray is to remove the step plate/lower runner guide moulding. There are a number of fastenings that hold the step to the body and these are well hidden in pockets beneath the tread under removable (well disguised plugs) once these are removed with a thin blade screwdriver and careful levering they reveal a number of Torx bolts. These protrude to the underside of the van and in many cases benefit from a wire brushing and penetrating oil from underneath before attempting to undo them. In addition to the selection of fasteners on the step tread, there is one either side on the raised sections at each end under a plastic top-hat plug (25mm diameter) once removed with the small clip-in plastic loom cover at the bulk head end the step will lift out revealing the cable and tray.

Mercedes Sprinter VW Crafter Side loading Door Cable Management Issues 3

There will be a huge amount of debris, soil, nails etc under hear and now is as good a time as any to clear this area out so as to prevent any build up obstructing or wearing the roller on the lower guide of the door track.

Mercedes Sprinter VW Crafter Side loading Door Cable Management Issues 4

Under the step is a black plastic flat cover, this clips into a raised plastic U section that supports and guides the cable chain tray as it rolls in and out of the step as the door is operated. The chain tray is attached to the U section by a snap clip that ties it to the bulk head end of the U section. As my chain had lost two links through damage I moved this by the appropriate amount further along the U section to compensate for the missing length. I simply cut a new slot with a craft knife into the U section and snapped the locator into the section.

Mercedes Sprinter VW Crafter Side loading Door Cable Management Issues 5

The clip in part that resides under the lower roller arm of the door was a little tricky to put back into place as both the electrical cable and latch cable run in slots either side of the moulding, these want to slip out as you attempt to clip it together. The electrical cable lies in the moulded lower section and hooks round into the chain tray attachment lug and onward into the reminder of the flexible cable management. Once all clipped back in lace I added a couple of strategically placed cable ties to hold the end together, engaged in the metalwork.

Mercedes Sprinter VW Crafter Side loading Door Cable Management Issues 6

Test opening and closing the door without the step and watch to see how close the chain tray passes the door hold-back latch pin fastened to the rear of the step cut out. This will be close. Too close for my liking and probably the reason the cable management got ripped away in the first place. I loosened the latch pin plate screws and moved it up a small distance to clear the chain tray. Ensure the latch on the lower runner arm still meshes with the pin and aligns well.

Mercedes Sprinter VW Crafter Side loading Door Cable Management Issues 7

Once the cable tray is attached and tested free to move, the step section can be refitted and the fixing pocket retainers refitted. The door should now be just as it was before the cable tray got broken.

Mercedes Sprinter VW Crafter Side loading Door Cable Management Issues 8

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.


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


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.





Late model Sprinter / VW Crafter Front Wheel Bearing Hub Replacement


A noise that was unmistakably a wheel bearing in its last throws of life had grumbled away for a number of weeks before eventually becoming too loud for the driver to ignore and the van was bought in for attention. Once the front end was lifted it was easy to hear which side was the issue, simply by spinning the wheel a little and listening for the dry rumble of a worn bearing. On this occasion it was the offside or drivers side that required replacement.

Sprinter Crafter Hub Bearing Assembly - This would have to be removed and pressed into the cast hub carrier - Quite a job without serious tooling!

Hub Bearing Assembly – This would have to be removed and pressed into the cast hub carrier – Quite a job without access to some serious tooling!

The demands of the transport business dictate how this job is attacked in many ways. Speed of turnaround and the economy of ‘time off road’ are the most important factors and this job is one that if done in the manner described can be completed in under two hours – if you consider any other way, unless you have access to some serious pressing or tooling and a few unexpected new parts along the way, then the long-hand method is best avoided – believe me!

Used complete hubs are plentiful as they are interchangeable between Sprinter and Crafter models so its pretty much ‘anything will do’ as long as it is the correct side. You can pick up a used item with fitted ABS sensor (necessary as 99 percent of the time they will break on attempted removal!) for around £60 – £70 often cheaper, once you have located your spare part you are all set to sprint to the finish. The main issue in removing your own hub and pressing in a new £40 bearing is the difficulties and special press required. If you have to buy in the engineering expertise to press out and fit the new item for you, you can add another £30 cash tip to the job, plus your waiting time for them to do the job.. so the cost to keep you running is about the same – albeit with a used complete hub assembly and not new part. Add to that the possibility of the engineering shop breaking the ABS sensor, which would cost you another £40 plus to replace. Enuff said!

Sprinter-Crafter-906 Hub

Used replacement complete hub assemblies such as this one are plentiful and quite cheap to source for example from user vansevicesltd on EBay

So you have located your chosen spare part and are ready to install. Loosen the road wheel and jack the vehicle under the chassis subframe section that supports the wishbone eye bushes, get as far to the wishbone pivot line as possible as some of the steelwork that exists in that area, especially the U channel that runs beneath the engine, left to right, is only of light gauge and will collapse/bend on any attempt to support any weight on it.

Once the vehicle is in the air, remove the road wheel and wire brush the lower hub balljoint nut, steering track rod end nut and the two connecting strut/damper to hub bolts. Be sure to include all exposed threads, the cleaner they are the easier to remove. Spray penetrant and allow to soak.

Using a 30mm Hex socket and breaker bar undo the lower balljoint nut and run it off to just over the exposed threaded section. Use suitable packing beneath the joint to the ground with a short axle stand or wooden blocks and carefully lower the jack so a reasonable amount of vehicle weight is supported on the joint. Taking a heavy engineers hammer whack the casting to the front lower edge of the hub near where the taper of the balljoint is located, be sure not to miss and damage the boot gaiter or anything else that happens to be around. Usually two or three good blows will part the joint and once this is achieved, jack up the vehicle again to support its weight from the chassis.


VW Crafter

Use a 21mm Hex socket and breaker to undo and remove the steering ball joint nut, either use a lever type ball joint separator or the hammer method above to release that ball joint too. Undo the torx head recessed fixing that secures the brake disc to the rotating hub. Swivel the hub to gain access to the two caliper hanger to hub bolts. 21mm again and breaker will loosen these off, be sure to lever back the pads a little in the caliper to enable easy removal of the assembly off the brake disc. Removing the two hanger bolts completely, use wire to support the caliper assembly under the wheel arch out of the work area so that the brake hose does not get pulled or strained. Tap off the brake disc from the hub centre and place out of the way.

Ensure the ignition is off and key out before proceeding as any ABS sensor removal while ‘ignition-on’ could result in a fault code being set, possibly requiring clearing from the ECU. Best avoided if possible (extra time and money).

Using a 10mm socket remove the plastic nut just forward of the roll bar on the plastic arch liner, lever this out slightly and trace back the ABS sensor wire and unplug it from the connector block hidden behind. ABS is usually the lower of the two connectors, the upper one is the brake pad warning sensor wire.

Using a 21mm spanner to back the bolt heads, use the 21mm socket and breaker bar to loosen the two strut mounting bolts. Note at this point that the top bolt is a slot and the bottom bolt is a hole. This is to allow adjustment of camber angle of the road wheel and should be returned to its original position as much as possible. Normally the bolt head position is easy to relocate on the strut leg as it has left a clean area where it has sat, simply make sure you refit this top bolt to position on assembly. Drive out the two strut bolts while supporting the hub, once free, lower off the lower balljoint taper. The hub is removed!

Replacement is exactly the reversal of removal with the proviso that once completed you pump back the brake pistons from the brake pedal so there are no disasters on first road test.

This hub swap should only take in the order of an hour and a half to two hours to complete, which considering the perceived scale and enormity of the job is pretty good going and this procedure is very possible for the home mechanic to undertake and acomplish without little problem.

Mercedes-Benz Sprinter

Mercedes-Benz Sprinter

Later Sprinter Crafter Axle Swap – Tips & Notes

Mercedes rear axle replacement 1

For the most the later Sprinter Crafter axle swap procedure is covered in the earlier posting on axle/final drive removal/exchange (older Sprinter) here.

There are however a few ‘extra’ tips that may benefit you should you be contemplating the removal or exchange of your later Sprinter or Crafter (2006 on).

Mercedes rear axle replacement 2

Sourcing an axle can be a taxing time, trying to get one of the correct ratio, from a similar van and of course trying to keep costs as low as possible are the main trouble factors.  After a great deal of searching, we came buy a rather sorry looking axle from a low milage 311 LWB panel van, perfect for our LWB VW Crafter CR35 as they are identical fitment. Because of the state of the back plates that support the handbrake mechanism, or in fact ‘lack of them’ due to severe corrosion gave us great bargaining power with the seller as it needed obvious work before you could fit. The axle came to us in the end for £200 which was somewhat of a bargain!  Generally if the axle appears dry of oil leaks and exhibits virtually no ‘in and out play’ on the input flange (pinion) then it will be a servicable part. You can see here below the large amount of play in the faulty axle that was removed.

The steel backplates that support the hand brake mechanism and offer some protection to inboard side of the brake disc were badly damaged and rotton with corrosion. These had to be replaced. New original OEM brake back plates can be obtained as cheaply as £11.00 each if you scour EBay, and pretty soon they were delivered along with the axle for fitting.

Mercedes rear axle replacement 4

Drain the replacement axle as best you can in preparation for remedial work prior to fitting on the vehicle.

Mercedes rear axle replacement 5

You will probably want if possible to recover your ABS sensors from the original axle as it would be added cost to replace these if not totally nessesary.  I have yet to find a sensor that will just pull out.  Corrosion of the casting where the sensors sit is quite bad as they are located on the top of the carrier where moisture and muck always collects. Undoing the single reverse torx pin is usually not enough to simply pull out the sensor – you will need to be clever!  Spraying the area with penetrant may help but the use of any tool to pry or grip the sensor usually ends in tears, you will have to tap it out from the inside.  Follow the instructions below if you have a stubborn sensor that you want to recover without damage.  Once the drive shaft is removed a soft nylon drift or wooden dowel, tapped with a hammer will make easy work of removal.  Its not such a huge deal to remove the shafts from the diff you are removing as it makes the thing lighter to drop and saves you about £100 in damaged sensors!  Dont forget to file the sensor hole clean on the recieving axle to ease refinement before replacing the drive shaft/carrier.

Mercedes rear axle replacement 6

Stripping off the old hubs and corroded shoes didnt take too long as they fell apart quite easily!  Once access could be found to the four reverse torx bearing cap bolts, located behind the hub carrier on the end of the axle tube, a little blow-torch heat was applied.  This enabled them to be undone quite easily with a breaker bar.  Unscrew them all, exposing about 10mm of thread and tap the heads with a copper hammer.  The bearing cap will start to move forward and a small gap will open up where the backplate is sandwiched.

Mercedes rear axle replacement 7

Undoing the retaining pins fully, carefully tap the flange out of the axle tube and withdraw the bearing, bearing carrier, hub and drive shaft from the axle tube. Be prepared for a little oil, and try and pull the complete assembly out as parallel as possible with reference the axle tube to avoid damaging the seal on the bearing carriers mating face.  Once the shaft is removed, recover the old back plate and note the position/orientation of it. Recover the ABS sensor if required (See note above). Install the new backplates with the ‘cut-out’ next to the brake caliper mounting holes, slide in the driveshaft and locate its splines into the differential internal gear. Guide the hub and carrier back into position, making sure to align the hole in the brass coloured internal end cap with the ABS sensor hole in the carrier (only one hole, make sure it aligns correctly with sensor hole).  Refit the four retaining pins and re-tighten them. The backplates are now now installed.  You can either choose to build up the parking brake now or leave things until it is fitted to the vehicle.  Often if your used axle comes with usable rear handbrake cables, its easier to build everything up first and then just simply reconnect the cables at the compensator – the choice is yours.

Mercedes rear axle replacement 8

If you are interchanging axles between Mercedes and VW you may find the anti-roll bar to axle bushes are different types.  This does not effect the position of the upper eye bushes for connection to the drop links, only the type of bush used.  Mercedes prefer to use a D bush and VW use a round tubular bush for the bar to axle connection, obviously the support bracketry is slightly different to accommodate either, worthy of note if pre-ordering spares.

Mercedes rear axle replacement 9

Fitment of the axle is covered in the earlier post here, apart from the connection of the ABS wheel speed sensors and brake pad wear sensors it is identical.  Be sure to reconnect the handbrake cables before adjusting the parking brake shoes, as if you dont they are likley to be too tight once the cables are connected, make this your last job.

Mercedes rear axle replacement 9

Prize out the rubber fill level bung on the rear of the axle and refill with your chosen hypoid oil, though MB specify a synthetic grade oil for this differential there is a multitude of oils that can be used in this application without detrimental effect.  Consult a manufacturer application chart to help you choose.

These few notes in conjunction with the earlier article will hopefully assist you in carrying out this task, it should also help you to select a replacement used axle that is right for your budget, not being put off by some damage to the backplates and using it to leverage your deal.

Mercedes rear axle replacement 10


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



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