Mercedes Sprinter Intermittent Turn Indicator – Cure

Mercedes Sprinter Faulty Turn Indicators

More often than not the number one cause of indicator problems on the Mercedes Sprinter range is due to the failure of a small control relay located on the lower edge of the fuse board on the steering column.  Faults are usually intermittent function of the indicators and hazard warning lamps, ordinarily the indicator will flash two or three times as normal then stop flashing altogether.

Locate the fuse board by removing the plastic panel beneath the steering column, (turn-screw latch at top of cover) at the base of the fuse board you will see a thick red wire connected to a lug terminal this is +12 live constantly, be sure not to short this to the chassis! – look below this and you will see two small relays placed to one side.  The relay that is furthest from the thick red wire lug is the indicator control relay (OEM Part is usually grey in colour).  Replace this unit and test indicators.  The next items to check if this does not cure the problem are the indicator flasher relay module and column control stalk – but nearly always the problem lies with this small control relay.

Mercedes Sprinter Turn Indicator Control Relay Location

Mercedes Sprinter Turn Indicator Control Relay Location

Just a note: There is no conventional flasher turn signal relay, the one you commonly see as the main plug in unit on other vehicles, that controls the flash rate/duration etc.  On the Sprinter the flash module itself is an electronic device and forms an integral part of the fuse control box beneath the steering column and cannot be swapped out without replacing the whole of the fuse board.  This is however a very reliable component and is not often known to fail.  Read below for further information:

‘’ An electronic wipers, turn signals and engine start control module located within the fuse block beneath the steering column monitors the turn signal circuits and controls the flash rate of the turn signal relay.  The instrument cluster continually monitors the right and left turn signal circuits to determine the proper turn signal and hazard warning indicator operation, then flashes the proper turn signal indicators and the contactless relay on and off accordingly.  The multi-function switch, the turn signal relay and the left and right turn signal circuits to the instrument cluster can be diagnosed using conventional diagnostic tools and methods. For proper diagnosis of the wipers, turn signals and engine start control module within the fuse block or the instrument cluster circuitry that controls the turn signal indicators and the contactless relay, a Mercedes dealer scan tool is required. Refer to the appropriate diagnostic information.”

For use in fault finding your turn indicator system refer to the circuit/wiring diagram section here.

Sprinter Indicator Control Relay 12v

Sprinter Indicator Control Relay 12v

It’s also worth a mention to check the operation of the hazard light switch on the steering column, if this is not functioning correctly the indicators will not work properly as it forms an integral part of the indicator electrical circuit. Operate the hazard switch several times and check for intermittency.

If you still have problems and have tried all of the above you may begin to suspect the column control stalk, this is an expensive part to replace and you need to be sure before changing this item that it is the probable cause of the issue – try everything else first, it would be a shame to replace this part and then later find it was a £2.00 relay that was the problem.

Good luck !

42 thoughts on “Mercedes Sprinter Intermittent Turn Indicator – Cure

  1. Thanks for the info Steve,I have this problem when I bought My 2005 416 sprinter.changed the sender unit, was ok but the fault returned three months later, Seems to only happen when its cold. after driving for 10/15 minutes it comes good.I thought it may relate to the computer as I have seen this happen in industry on PLCs. I will go through your suggestions, PS there is an after market Bull bar fitted ,I thought the indicator earth may not be very good. But I have fixed them
    Regards Gary

    1. Hi Gary,
      I bet its a problem in the fuse board under the steering wheel covered in the blog, especially the push in column connector at the top. Strip it down and have a look, you may get lucky! Let me know how you get on.
      All the best

  2. I have a 3500 one ton dual , 2006 .
    I had the same issue with the turn signals working
    fine until you apply the brake, then they stop flashing,
    and partially light.
    I replaced the relay first, no change.
    Then I cut out the converter for hitch wiring!
    Work perfect now…just need to replace the convertor
    for the trailer lighting.
    Hope this helps
    Steve @ herndon electric

  3. Hi Steve
    Thanks for very informative posts – quick question (and hopefully related enough to get posted) – where do I find the signal relay on a W638 bus? I have had the instrumentpanel screwed out (thought it may be hiding back there) – and I have also tried to go through the fuse-box under the seat – but nowhere to be found. I have bought a new MB part 0035420219 – which should do the trick – but just don’t know where to put it :-/

    1. Hi Michael,
      There are some relays under the passenger seat, it maybe here. Operate the indicators and have a listen you should be able to hear where its clicking. Let me know what you find.
      All the best Steve

  4. Hello Steve,
    I’m so happy I’ve stumbled across this site/blog, very informative so thank you for that, but I’m struggling to find a solution or something to point me in the right direction as to what could be wrong with my bus, it’s a 2005 416cdi, when driving it a few days ago I indicated right and the indicator came on but didn’t flash, the indicator stayed on for the rest of the journey, no flash just a constant orange light until I turned the ignition off, at the same time as this fault accured the washer pump started to work, again constant until the ignition was turned off! Left hand indicator works as normal, hazard lights don’t work either!
    I suspected that the fault was in the fuse board so I fit one from a friends bus relays included, one that I knew was ok but still the fault exsists 🙁 Please help as I’m not too sure where the fault could be, where else are the washer pump/indicators linked in any way??

    Thank you in advance,

    1. Hi Nick,

      It sounds from what you describe, that you have a faulty column control switch assembly (the levers that control lights/indicators/washers etc.) This is not an uncommon part to fail. It sometimes fails in a way that turns off the headlamps when you indicate! I think if you replace this part you have a high chance of fixing your problem. The two lever controls left and right are one switch assembly.

      All the best

    2. Something I should add is that the wipers were also operating even when not turned on, switching off by themselves and then back oin again! Also when I fit the doner fusebox I tried it both plugged in to the switch unit (handlebars) and separate, both with the same outcome- right indicator on and washer pump buzzing away!


      1. Thanks for your reply Steve, but I’m still at a loss to solve my problem!

        So with the fusebox dropped down and not fitted to the switch (handlebars) switch but still with all the block connectors fitted I still have my right indicator on (not flashing) wipers going constantly and washer pump going constantly! I’ve tried 3 different fuseboxes, I’ve also stripped 1 of the fuseboxes to clean up the spade terminals.
        I’ve tried a separate Earth from battery to engine and from engine to chassis but nothing seems to cure the fault.
        I have noticed though that by removing fuse 17 and putting it back in it does cause the indicator light to flicker, sometimes if I do it enough times the light stays off but the wipers still contine! Aargh it’s driving me insane.


      2. Hi Nick,
        The modules that control the washer pump, wipers and flasher circuits are all built into and part of the fuse board. Because of this, there is nothing else ‘in circuit’ between the output from the board to the external devices.

        If you have swapped the fuse board and the fault still exists it could only be external to the fuse board. In other words the loom could be damaged somewhere applying +12v to some lines (Washer pump and indicator). However if you think about it, it pretty much defies all logic.

        For example – For the washer pump to run, there must either be battery + voltage on the supply wire to the pump or from a controlled output from the module, invoked only by the multi function switch.

        I know this is kind of a strange thing to suggest but are you absolutely sure you have the correct plugs in the correct sockets on the fuse board? The only thing I can think of as a remote possibility is that two are swapped over, giving the same fault on all fuse boards you fitted? Is this at all possible? You may be able to identify the some of the wiring colours from the photos on my ‘fuse board page’ and check things are in the right places.

        I cant be of more help I am afraid without being able to measure exactly what is going on.

        Do you have a tow bar fitted? If so the additional indicator relay unit (at the back somewhere, could be faulty – back feeding a supply up the indicator wires to the fuse board control unit) If you have one of these remove it, and then test your indicators etc.

        All the best

  5. Thank you Steve,
    I’m 99% sure that they’re in the correct position but I’ll double check. I’m of the same opinion as you that it’s got to be in the fusebox where the fault lies but why doesn’t a replacement solve the problem? Dodgy plugs maybe or as you suggest a damaged loom, I really hope it’s not the later!!
    I’ve looked on your fuse board and can identify some of the wires, any suggestions where I could get a wiring diagram from?


    1. Nick,
      Don’t forget the tow bar indicator relay, even if there is no bar on now, it may have had one fitted and the module is still in existence in the rear somewhere – probably awash with corrosion and waterlogged!

      USA Manual but in many ways the same. Look at the mid pages for electrical diags etc.
      HERE – 32Mb large file so you will have to right click and ‘save target as’ to download it to your local drive.
      All the best

      1. Well my electrical problem has raised its very ugly head again!

        It never really got sorted the first time around it just seem to right itself so I’ve carried on regardless. This time it’s come back but with twice as many problems, symptoms…. with ignition off I turn the side lights on and the instrument panel lights up like a Christmas tree, as if the ignition has been turned on, the blue main beam is constantly lit up as well as the right hand indicator arrow and also washer pump motor is buzzing away!! I’ve tried 2 different handlebar switches and 2 different fuse boards but the faults remain.
        Any ideas or can recommend an auto electrician in the North of England?


      2. Hi Nick,
        Sorry that it is still playing up.

        As you have looked for broken chafed/wires in the loom under the dash, I am going now to put my money on a bad earth (brown wire) connection somewhere. MB use Brown wires to earth circuits at different points on the vehicle chassis, usually several cables meeting in one point on crimped eyelets that are bolted to a single ground point (Star earth/ground connection) If the connection to the chassis is ‘bad’ the returning voltages that should be going back to the battery via the ground connection get back fed into the other connected systems – and you get very unusual electrical goings-on.

        Start by looking at all the brown wires connected at the battery tray/inner wing area (there are a few), undo these and clean them up including the part of the body they fix to. Then look carefully at the grounds of the rear lamps and clusters, trace the brown wires back to where they connect to the chassis – infact pull off the connectors to the rear lamps and see if the fault magically goes away! (Side bet here on this being the issue, as the rear lamp clusters and holders are known for rotting! – who knows!)

        Have a look here for evidence of this issue, although in this case it is an SLK car: When the boot earth/ground/brown wire was broken to the boot lid, when the guy opened the lid, all the dash lights came on ! Sound familiar?

        Good luck and do let me know how you get on – any brown wire check it out, even by the headlamps either side of the lamp units on the inner wings.


      3. Hi Steve,

        Success at last!!!!

        The final straw came a few weeks back when my turbo stopped working on the way back from Manchester, no boost pressure making those hills such hard work!

        So enough was enough…. headlamps out, grille off, bumper, the lot.
        Initially I thought the reason for no turbo was a faulty boost pressure actuator valve (underneath air filter) but having checked for 12v supply there was a reading of 2-3v. I traced the wiring back stripping all the insulation off and there it was…… a cluster of 5 or so wires located underneath the radiator on the near side all rubbed through on a small 8mm bolt!!!! Soldering iron out, insulation tape and many cables ties later all the electrical problems were cured!

        Thank you for all your advice Steve, I hope this helps others in the future should they experience similar problems.

        Keep up the great work.
        Best wishes,

      4. Hi Nick,

        That is fantastic news, its a great feeling when you finally discover the problem’s root cause. There is also another loom area behind the grille on the left hand side (looking in) where the horn wires come over from the main traversing loom and connect to the sounder. There should be an edge protector on the upper seam of the front cross member where the wires pass over it, but invariably this comes off at some point – result, the horn wires rub though! If you ever lose your Sprinter horn suddenly always look here first..

        All the best

  6. Hi Steve,
    I have a problem with smoke on idle, 2007, sprinter 311
    240 k miles its been on a star diag machine, and the only fault that was in there related to the glow plug relay, (light displayed for 30’s on start-up) having replaced the relay the smoke fault is still present as it was before, it uses no oil or water, and cooling system block test is negative, fuel mpg is excellent and on a run regulary does 31-33 mpg, if you keep your clog off, its had turbo remand at nottingham, injector values on star are all well within spec, had it on a smoke machine to test for air leaks, nothing there, new cat and dpf was blown out at same time, (no soot in there anyway) even doing a forced regen the values recorded are less than 3% only bad thing that seems to happen is dilution of oil with fuel,and the need to drain excess fluid off from sump every couple of months, and the bulb failure light displays constantly with lights on (all bulbs functioning ) ( brake light switch replaced 18 months ago with ecp one)
    basically you can drive all day long and not have any smoke, unless you stop and idle engine for anything from 2 minutes and you have white smoke when pulling away, idle for 20 minutes and someone could be calling the fire brigade.
    any help would be very helpful even if you pm me,
    many thanks.

    1. Hi Robert,

      From reading your detailed description my first guess would be that the engine has worn bores/rings or both. The fact that there is dilution of the oil with wash down diesel is making me think this way.

      What you need to do is pull off the breather hose from the oil separator on the rocker cover and see what smoke you have there. You can also get a sense of how much pressure you have in the crankcase by lifting the dipstick out of its tube a little.

      Mercedes pipes its crank case fumes passage directly into the turbo intake to be burnt in normal combustion. If there is bore wear present and quite a bit of blow-by when warm, it will start to mist up the turbo and intake tract with oil at idle. Long idle periods and the oil residue present begins to build up in the intake tract and intercooler and will then get picked up and transported to the combustion chambers to be burnt off when you rev the engine or get moving again – holy smokes!! Obviously after a few seconds of high revs this will clear until you next idle.

      To confirm my suspicions you would have to get your dealer/mechanic to do a base-line compression test, comparing it to allowable specs and see exactly what is going on inside the engine. They usually do this quite simply with a diesel compression tester fitted to the glow plug apertures once removed.

      If everything else you say rings true and there appears to be no over-fuelling (usually black smoke) and the turbo seals are good (recent turbo) then our options of another cause are quickly diminishing.

      The fact you say it uses no oil could be slightly skewed by the fact that the wash-down diesel is replacing any over-normal oil consumption, it would be really hard to tell and estimate any oil usage/burn as other fluids are being added to the sump oil.

      What do you think?, well worth investigation…
      All the best

  7. can you tell me where the indicator relay is in a 2008 crafter,,can’t find a photo,,,,indicators flash externally for 10/12 secs then off ,,,dash indicator continues as normal

    1. Hi There Damien,
      The design of the later Sprinters 2007-on (NCV3) have a slightly different layout. The indicator/flasher function is handled by the body control module BCM that forms part of the fuse panel under the passenger kick area by the bonnet release. See here: and here: There is no physical flasher relay to look for at all as this function along with many others is handled by the internal electronics of the BCM. Your problem is most likely a fuse/poor contact in the above location or a BCM power issue, rear lamp cluster/bulb holder corrosion/fault or possibly problematic stalk controls.

      I hope this helps.
      All the best

    1. Hi Ethan,
      I will assume your model is early Sprinter before 2006. Check fuses under the steering column, remove the top securing nut from the fuse panel and make sure the two connectors at the top are clean and well made. Check all the wiring on the rear of the fuse board and pay special attention to the relays at the base of the fuse board by the power connection. This article may help.

      All the best

  8. hi i have a 2012 freightliner sprinter van 170 inch wheel base numbers 204d and 205d flashes where the mileage numbers are some times anyone else see these numbers any help would be greatful thank you

    1. Hi William,
      I can honestly say I have not come across this and have no clue as to what it should be. It seems strange and I have a feeling that there is an issue with the speedo cluster display driver as this is what happens when this component has an issue. As it forms part of the electronic circuitry of the instrument board it is likely it will need replacement at some point. Check with a good independent shop or dealer and see what they say. Try and photograph it on your phone if its intermittent then at least you will have something to show!

      Let me know what you find.

      All the best

  9. I have a 2010 313 the indicator in the mirror on the near side has stopped working showing a bulb out when that side is applied I changed bulb unit but problem is still there ? Any help would be much appreciated
    Thanks in advance

    1. Hi Patrick,
      Thats strange. The bulb holder itself could be corroded. Best bet would be to measure if voltage appears at both the electrical connector. Examine the holder and ensure that it is making a good connection, it should only latch into the lens assembly in one way. If still no joy and you cannot measure any voltage either with a test lamp or test meter then there is a chance the wiring may be damaged and you would have to strip the trim panel from the interior of the door to investigate further.

      Hope that helps.

  10. Any idea about this fault on a Vito W639. I have no indicators, the cluster light flashes at double speed, but no light outside, the hazards click at normal speed but nothing outside the vehicle.

    All bulbs and wiring that I can see appears ok.

    SAM unit?

    I cannot find mention of a relay or a fuse for the indicators on a Vito

    1. Hi Mark,
      There is a control relay, Mercedes call it an ‘interrupter’ in the indicator circuit. This is the item you are looking for. Sadly I don’t have a diagram for this vehicle but the relay will most probably be around the steering wheel area. Often if there are ground faults on the lamps at the lens end/to body it usually only effects the side the poor earth is located on, make sure the brown wires are clean connected to chassis.
      Hope that helps.
      All the best

  11. Thanks, struggling to find a part number on this part to order if from a factor, rather get a new one than a used unit

    1. Hi Mark,

      I have one last idea, do you have a tow bar fitted or have had a tow bar fitted? There is a module that is fitted to control the trailer indicators, sometimes this is either under the vehicle at the rear or in the rear quarters just below the rear lamp clusters. It can fill with water and play up. If you don’t have the tow bar it can be disconnected as it just provides signal to the trailer without interrupting the bulb fail circuit. Perhaps you are correct regarding the module within the front SAM, the Sprinter for sure used a fuse board control with no relays for the indicator circuit.

      I only have access to sprinter diagrams and nothing for Vito, you are most welcome to browse the Sprinter manuals if there is anything that will help you out here – Though there is a good link here to locate body earths etc. Sorry if the listed relay unit turned out to be a red-herring and I was wrong. Did you eventually find out for sure what you suspected was correct?. Any information to share would be great if you could pass it on to assist anyone with similar problems.

      All the best

  12. cant really find them listed anywhere aside from those second hand part lookup site, even ebay doesn’t have any listing for this current or past auctions

  13. sadly even the site in your link, if you search for the part, says it cannot be found, Vito 639 have this unit?

    I keep reading that indicators are controlled from the SAM?

  14. Hi Steve,
    My off side indicators are not working in normal use but they do with the hazards .
    Any ideas?

    1. Martin,
      If you cannot get things into life by pushing the fuse board under the steering column, having checked for any bad connections here – then there is a high possibility the combination switch is faulty (indicator stalk combo).
      All the best

  15. Hi I am hoping someone can assist. I have a motorhome on a 2004 Sprinter 416 CDI base vehicle. It has been parked up over winter and I have been checking round it getting it ready for summer. I do not appear to have any front or rear side lights, no headlights dipped or main beam the indicators work ok but not on the hazard light switch. I have checked the obvious bulbs fuses etc but cannot believe they would all have a problem. I would welcome any advice to solve the problem or does it need a Mercedes code machine..
    regards Keith

    1. Hi Keith,
      All power is distributed from the under steering wheel fuse board on the column. If its all off in that number I would be looking at the column multifunction switch – either the switch itself or the fuse board connector as it interlocks into the multipoint plug at the top just under the base of the steering wheel. Push the fuse board or bang it, see if it comes to life!

  16. I have a 2017 Thor Citation 24 SS on a 2017 Sprinter chassis. I have a RH turn signal blinking very fast and the LH is normal speed. It also has a “RH Warning” symbol on the dash panel. I’ve looked at all the fuses under the dash board and drivers side panel, no bad fuses. All bulbs are flashing when I turn on the signal, no bad bulbs, the hazard lights work properly as well. Any other ideas or areas to check?

  17. Hi There Thanks for the info . My 2005 om647 turn signal lights just suddenly stopped working all other lights are working fine . Im going to swapp the wiper and turn relays and see what happens

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