W202 Diesel ABS Light On

steve kane

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Hello, I thought I ought to start this as a thread of its own. I have today started to look at our ABS problem, a few weeks ago we noticed the ABS light was on. The actual sequence is that the light comes on with the ignition, goes off for perhaps 2 seconds when the engine starts and then comes on again, all whilst stationary. I have today taken a quick look at the Wheel Sensors which look okay, the cables look to be in good condition and I pulled the ABS twin plugs from their connectors under the wheel arch and sprayed them with contact cleaner, they looked to be in very good condition anyway, I then pulled what I think is the Over Voltage Relay (on my car its in with the Cruise Control gubbins and has a pair of 15a fuses under a clear plastic cap on the top) and sprayed the pins with cleaner, but none of this has made any difference, is there anything else I could check or should I be scouring the scrap yards for wheel sensors? BTW does anyone know whereabouts the ABS control box/module located and how do you get the blue multi plug off of the side of the ABS pump, I got the caseing to slide up by perhaps 15mm but the plug was not shifting and I did not want to force it, I was going to spray the pins there too.
Steve.
 

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Hi Steve, the ABS control unit is in the box and 116 in this link.


There are very few 202 cars around with an OVP relay many faults can be had with the connector on the ABS module.

Do not forget the sensor on the diff
 
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steve kane

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Many thanks Malcolm, does the fact the the light goes out and then come on again after a few seconds mean anything? I am yet to trace the sensor on the diff but one thing I thought I ought to check is the boot area, does the wireing for the rear sensor come into the boot I wonder? When you say that the Over Voltage Relay is not often found on the 202 was that not an OVR with the pair of fuses on the top that I had found? Many thanks for the link to the parts diagrams, though I must admit Im struggleing to recall seeing anything that looked like the drawing of the ABS control box on my car, is this bundle of stuff located centrally on the bulkhead as it apears on the drawing? Sorry about all the questains but really not too sure what Im doing when it comes to ABS.
Steve.
 

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The light will go out when the abs control box is re setting during the starting cycle, and this is normal. You can see the part number for the control unit in the link, so should be straightforward to find the right box,,it will be made by Bosch

I think that it is worth measuring the sensors for the resistance they should all be about the same. You could get a read out from STAR
 
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steve kane

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Many thanks Malcolm, is there a specific resistance they ought to be or is it fine if they are all roughly the same? I will probably kick myself afterwards but,,,whats "STAR"?
Once again, many thanks for your help,
Steve.
 
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steve kane

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Malcolm, I have been out to the car again this afternoon and had a quick look under the bonnet, to be honest my set up looks nothing like the exploded drawings and I cannot see anything looking like part 116. My car is a w202 Non Turbo Diesel which is a P Reg, looking from the front I have in the far l/h corner the fuse box with another sealed box behind it secured with screws, there is nothing on the central part of the bulkhead, in the far r/h corner under a large plastic panel is the Cruise Control mecanism and sitting behind this the ECU, this is just a single unit in its own cast alloy bracket, beside it is a large Relay and in front there is what I assume to be the Over Voltage Relay with its two fuses under a clear plastic cap. There is really nothing else that I can see that resembles an ABS unit?? Would it be helpfull to you if I were to provide the vin number?
Steve.
 

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Give me the next 3 numbers after 202 please and the year
 

BlackC55

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before you start bolting parts on your best bet is to get the fault codes read
 
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steve kane

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Hello Malcolm, the 3 numbers following the 202 are 125 and the registration date is 03/10/95.
Many thanks for the offer of a Star dianosis, I will take this up if I cannot easily locate the problem myself, my only slight concern about computer dianosis and fault codes is that I have read of people having elderly cars "read" and the computer throws up all manner of faults none of which actually solve the problem, I have no personal experience of course and perhaps you only hear about the problems but I do wonder if older cars have so many dodgy connections, poor earths etc that expecting everything to measure up perfectly for the computer is a little too much to expect? whats your opinion/experience BlackC?
Steve.
 
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steve kane

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Hello Malcolm & BackC, any further thoughts about my ABS, Malcolm, was the first 3 letters of the Vin number you asked for of no help to you?
Steve.
 

Alex Crow

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hello steve. you will find the abs controller under the metal panel in the passenger footwell, behind the carpet against the bulk head. i have known these to have water damage to the pins, unplug it and see. did you say you have resistance tested the front sensors? this is worth doing. the rear sensor may well have the connector under the rear seat. and yes, that is the ovp relay!! good luck.
 

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Sorry Steve I missed this,,I have sent you the chart showing the location of all of the components, also a chart of all of the voltages to test
 
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steve kane

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Many thanks indeed to you both, its really very much appreciated, I doubt I would have ever found the ABS Control box, sounds like a "backbreaking" job to get at and I think my first job will be to pull it out and give the terminals a spray of Contact Cleaner. I have not as yet tested the front (or rear) sensors but I trawled through the ABS posts I could find last night and found the thread from the Irish chap who had a good mixed bag of ABS problems, he was quoting resistance of 1000 ohms I think but I really need to check this figure out, but I also thought that if they were all coming up at around the same value then that probably meant they were okay. Later today I will have a really good look through the attachments that Malcolm has sent, and will of course let you know how I get on,
Once again, many thanks to you both,
Steve.
 
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steve kane

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hello steve. you will find the abs controller under the metal panel in the passenger footwell, behind the carpet against the bulk head. .

Hello boys and girls,,,well I spent some time looking at the diagrams TV kindly sent through but these clearly show the ABS eco/controller being situated in with (or even part of??) the main car ECU beside the Cruise Control mechanism, there is nothing like this set up on my car, so after reading Alexander's post and after a rather doubtful poke around behind the passenger footwell carpet there was the strangest set up I have ever seen on a car, a large metal plate which it seems you can just pull off the threads of what look like PK screws sticking through the bulkhead, the metal tabs which are bolted to the floor just bend and you can hinge the whole thing down, and fixed to the back of this plate was a pristine looking box with a label stating that it was the ABS control box, there were two large multi-pin connectors and after pulling these off and unscrewing the box I could see that everything looked nice and clean, never the less I gave it all a good squirt of contact cleaner but of course none of this made any difference and the ABS light is still glowing away. Still at least I now know where the ABS box is if I do need to change it. Next job is to check the Sensor resistances,,,hopefully the fault will be there,,
Once again, many thanks for your help,
Steve.
 

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The changes drive you mad on some cars 4 different versions and layouts,,though in normal life the front sensor give more problems, it is the rear on these cars that do.

You should measure the voltages on the ECU before doing anything else
 


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