Mysteries of the Mercedes Sprinter road speed signal – ABS

The Story…

A long wheelbase 4 cylinder Mercedes Sprinter (2004) some years back had ABS problems and the ABS pump was bypassed at the time due to the unavailability of parts and dealer cost of a new replacement unit. The Sprinter ran for many years, each time passing the annual MOT with no ABS function without problem – until the recent changes to the MOT test. The new revised regulations for the MOT test stipulate that if the vehicle has ABS fitted it must function correctly – at least with regard to correct function and sequence of ABS warning lamps on the dash.

Bosch-5-7-ABS-Pump Mercedes Sprinter

The owner had been told by the MOT inspector that if the ABS system was totally removed from the vehicle it would not be subject to test inspection. He was advised to remove the faulty ABS pump and remove all wheel sensors and wiring. Once this was done a pass certificate would be issued. Pump and sensor wiring was cut back, sensors chiselled off and the new MOT certificate obtained. One problem – no speedo function and Limp home actuation in higher gears (3rd upward)

I had the van to sort out as it was basically un-drivable and did not have a functioning speedo/odo.

The Mercedes Sprinter (ABS model) takes the road speed signal from the front left ABS wheel sensor.  Once this wheel speed signal is restored and the ABS pump module reinstated (this self contained unit contains the ABS control electronics) the speedo will function as normal.  The wheel speed data pulse will be signalled to the ABS controller then data sent via CAN BUS to the Engine ECU and speedo unit.  Road speed will be once more indicated and the ECU will have its required speed input allowing the engine electronics to operate correctly throughout the speed range.

Wheel Speed Sensor Mercedes Sprinter

Once these few but critical components are refitted, (although the ABS was not or would never be functional in the above case) normal service is restored.  It may also be noted that if you have a Sprinter with fitted and functioning ABS – If you ever get an ABS warning light in conjunction with a loss of speedo reading, it will most certainly be the left hand side front (when sitting in the drivers seat) wheel sensor, its wiring or reluctor (tone wheel) ring  that is faulty.

A special note from the owner of the vehicle – Always take what MOT tester’s instruct you to do with ‘a pinch of salt’ as they most likely don’t know anything about the intricacies of Mercedes Benz models or their control systems.  This turned out to be quite costly advice that was given freely. The moral of the story is: If you are unsure, ask some one who actually knows!  🙂

14 thoughts on “Mysteries of the Mercedes Sprinter road speed signal – ABS

  1. i have a mercedes sprinter model 316 2.7 2004/2005 with abs pump numbers on bar code sticker 4902950265 / 900 043 / 085 2093 and on the brake pipe fitting side 000 446 56 89 /0 265 224 085. the issue i have is the EDC ABS BRAKE WARNING LIGHT AND WHEEL SPEED SENSOR LIGHTS are all up on the dash when driving vehicle and no speedo. The vehicle will not communicate via its scan socket (round type)checked the fuses listed under the steering colum and side of the drivers seat we have tried various different scanner makes and models can scan engine with no issues so removed plug of the abs unit checked for corrosion water ingress but that is all good checked feeds to plug which shows feeds. sent abs unit of to be tested no faults found and no issues communicating with it so there is an issue on the vehicle. Do you no apart from fuses under the colum or drivers seat there maybe other fuses and cannot find a wiring diagram for that make and model vehicle with that abs pump fitted or if there are other issues we need to be looking at or for. thanks for any assistance

    1. Hi there Phillip,
      As you have no speedo, I would guess that there is a problem with the left front wheel speed sensor, as sat in vehicle. It would be advisable to get a code read to confirm to prevent you changing out good parts in error, but that would be my guess.
      It could be the sensor itself has pushed away from the tone ring slightly but physical inspection would prove this. It will push back in to almost contact the tonewheel, a paper thickness clearance. Inspect also the slotted wheel tone ring for damage as well as obvious cable damage to the sensor.
      There are not many code readers that can access the ABS system an on some models I have only found that carsoft V12 and their interface or Mercedes-Benz Star are the only tools that can access the system. I am not suprised of your findings.
      Hope that helps

  2. I have sprinter 2008, when speed control module S.C.M is connected it will not rave up,
    If I remove it, the ABS /brake /ESP/ADR/AND ENGINE lights all comes on.
    part no for S.C.M 898078000

    1. Hi Leo,
      I would be looking to check throttle pedal position sensor and wiring first off. Poor fuel supply/low fuel pressure would also have a very similar effect. What codes are returned when you read OBD?
      Best Regards

    1. Hi George,
      This will be CANbus communications and is in the data connection between the ABS unit and the ECU. You will have to pull some Bosch diagrams depending on the module type fitted. Grab the model number and get Google on the job!
      All the best Steve

  3. Have a 2014 Mercedes Sprinter van RV. Recently sprayed underneath with a Mouse deterrent spray. On next trip shortly (250 miles) after the spray the ABS and ESP lights came on. As I understand this could be an ABS sensor problem.
    Ouestion? Could the spray (a gel like thickness) somehow be the culprit?

    1. Hi Robert,
      The front ABS sensor cable connectors are well hidden and protected, the rear axle connectors are not so. There is an outside chance the gel has made its way into the connectors somehow. Usually you can find these on the rear chassis section, if you follow the cables up the handbrake runs from the axle to the chassis. Remove them, unplug and clean. Test and see if any better, seems too much a coincidence that it happened after the spray treatment.
      All the best

  4. Just a quick heads up.

    I removed the complete ABS system from my vehicle, this entailed removing all sensors & wiring, the pump etc, replacing all the brake pipes & plumbing them for a non ABS setup, changing the master cylinder & servo to a non ABS spec one, installing a brake proportioning valve to the rear brakes to limit brake force on the rear brakes & hours spent on the web, to find out if it was legal.

    It’s only legal to remove it, if the option to have it was relevant when the vehicle was bought new!!

    1. Hi Phil,
      Thats probably the DOT MOT Testers manual view, however in reality if the system was removed and there was no ABS remaining, warning light or otherwise, the physical function of the ABS is not required to be tested so its actually a farce. I have taken in the past road-registered track cars that have had vacuum servos removed from brake systems (replaced with pedal box compensators and custom performance non-servo brake master cylinders) The book braking efficiency was met and they did not fail by result of not having a servo, even though the production variant had that option as standard. As long as the vehicle ticks the testers boxes on the sheet and performances are met then there is little to cause difficulty in obtaining a pass certificate.

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