ESP/ABS inoperative - a couple of easy diagnostics

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sceh

Active Member
Joined
Jul 31, 2015
Messages
244
Car
w123 240TD
Seems to be a common problem and you can find a **** post from me further on after finally cracking the problem.
Here is what I learnt.
If you are driving along and these warnings appear you can draw three conclusions:
It is not the reluctor or impulse ring
It is very unlikely to be the ESP or ABS electronic unit
It is one of the sensors with a bad contact where it is plugged into the wiring harness and not the actual sensor itself which is pretty bombproof.

If you switch on the ignition and don't move the car or start the engine and you get these lights, it is the sensor connector
If you have these lights after driving, clear them and then see if they come back when you switch on the ignition and don't move the car.

If your car is a rusty old banger then yes, it could be the impulse ring of the old type

Why is this?

The car will signal a fault if it detects no circuit to the sensor which happens only when there is a bad contact ( reseat the sensor plug)
When you move the car and one sensor is duff then there is a DTC to say 'implausible signal from wheel speed sensor'
The car detects movement via all or any of the sensors and only then will it raise the above DTC and the ABS/ESP lights - otherwise not.
If all the sensors have electrical contact and no bad contacts and the car is NOT moving and there are no stored DTCs, the ABS/ESP lights won't light. Clear DTCs to test this.

I spent a lot of time chasing the reluctor ring and learning how to change it but it was a wild goose chase. It is a static component and will last decades unless rusted to death.

Moral. Reseat the sensor contacts first
 
I like your problem solving methodology; trouble is there is always an exception to every rule with cars!
I had an issue with the front sensors on my 50,000 2013 S204. Both failed within a short period of time of each other and one of the reluctors packed up :wallbash:
 
I wish I had the monopoly on problem solving but alas...
Sensors failing within a short period of time of each other could be just coincidence but when you changed the reluctor ( a magnetic type I assume) was it broken or demagnetised? Either is a bit odd and breaking would be the most obvious because demagnetisation will only occur after a lot of hammering or the presence of a strong magnet.
Sensor connectors on the front of the W204 are a bit odd and a combined plug for sensor and brake wear indicator and easy to install with a bit of a wobble. Did you do the jobs or did Mercedes? TBH, if Mercedes changed the reluctor I doubt it was duff....but I am sceptical by nature
 
On my W211 it was a faulty SAS that threw up this problem.
 
Of course the SAS is used by the ESP and DSC and emergency braking and so on and all of these rely on knowing wheel speeds, as does ABS. All of these functions are inputs to the Bosch ABS unit and, depending on how the application level programmers see things, you end up in the dreade cause/effect loop. For example, if the SAS fails or gives a bad signal, which warning lights do you light? If the Wheel sensor gives bad signal, you have an ABS light but but no cars I know of have a sensor warning light or a n SAS warning light. So you end up in a situation where you don't know what caused wht and in the case of some cars (my worst being the jokes they call Landrovers) a duff brake light (needed in the HDC system since it puts brake lights on automatically when descending a hill) can, and will, lead to limp mode, lowered suspension, gearbox failure warnings, gearbox locking etc etc.
Curiously, most cars use the BOSCH ABS unit but it then depends on whether the (designers' then use the outputs to provide warning lights or, as in the case of LR, total disaster. Nothing gets your attention quicker than overtaking a lorry at 70 on a motorway and the car decides that limp mode is a good idea..
So, in this case, was it the actual SAS broken (most likely just a bad contact btw) or the wheel sensor or something else?
Frankly, the worst thing to ever happen to cars was the CAN bus system in the hands on non-IT experts
 
To clarify. The CAN bus is a great CSMA/CD bus but someone, somewhere has to write the code in the various ECUs to decide what to do with the signals. Mercedes is pretty good and I have not seen any wildly ridiculous treatments of messages. The ECUs also drive the warning lights of course. Also the buss allows messages to be sent but you can't reply to a message or interrogate something. So, you can't get an ECU to ask a sensor if it is OK or not. The sensor sends a message and that's it. The ECU then has to decide what to do or send a message to another ECU.
The higher level software determines the action. In the case of s wheel sensor Mercedes decided to switch on the ABS warning light together with the other subsystems affected like ESP, DSC etc.
Land Rover and some others do other things, some of them stupid. This is where the problem lies
 
Currently having this issue and scratching my head.

2013 ML350 Bluetec (diesel) 271 000 km. Was driving on the highway a month ago and then my dash suddenly turned into a christmas tree (ABS, ETC, ESP, yellow parking brake icon) all illuminated. A bunch of messages appeared and lost my cruise control. Check engine light appeared. I arrived home and plugged in my OBD reader and got a code for rear right abs wheel sensor. I ordered a new one via Rockauto (aftermarket, non OEM) that had good reviews. I changed the sensor myself. All was good for about a week.

About a week ago, I was cruising down the highway when I hit a patch of rough road/bump and then the christmas tree appeared again (same symmptoms as before). Scanned it and again, same diagnostic. Rear right wheel sensor. Now I'm scratching my head. Is the sensor not good? Is this the wheel bearing (I doubt this is the culprit)? Is it the reluctor ring? I have no idea where to start now. I'm no mechanic expert as well. I can only do basic stuff.

Any suggestions? I've heard some people saying a bad/old battery can cause this (my main and aux batteries are still original (10 years old). I'll replace them both this weekend and see if that helps.
 
Not the battery or the reluctor or the sensor itself. You have a bad contact and the most likely place is where the sensor plugs into the connector under the wheel arch.
Unplug it and switch off the ignition and clear codes. Check the contacts and the plug are clean and plug it in a jiggle it to be sure it has a good contact. Switch on the ignition . If you have a warning then it could be that the actual sensor is duff Try another. If another gives the same problem, the fault is somewhere else but it is certainly a bad contact which gets out of whack when you go over the bump. Ignore ALL the codes and lights and welcome to the world of the stupid ODB and CAN bus system!
let me know what happens and then we can go the next steps. Do NOT change battery or anything - waste of money and won't solve the problem
 
Two other things to check are the SAS (Steering wheel sensor) contacts - it is the device around the steering column under the dash. Don't remove it because the chances of it being bad are close to zero since it is passive device. Just jiggle it and it you can reach the plug, unplug it and replug it. Ditto, the brake pedal contact- This *could* have a some conducting dust inside due to age but same procedure. It is a simple switch usually sourced from Ford.
For sure though, it is not the reluctor, battery or ABS system itself although a garage might tell you otherwise :)

Why could the SAS or brake switch cause all these lights? Rewind the the stupid ODB system higher level applications. ABS, ESP, ETC etc all need both these to work 'properly' and if, for example, a wheel sensor is duff or the contact is bad, the ABS system doesn't work and if the ABS doesn't work ESP, DTC and everything else gets mixed up etc
 
Thanks for the reply Sceh, I just noticed this morning. A couple of days ago, I removed the wheel and wiggled with the sensor to make sure the connection was snug. I put the wheel back on and then proceeded to change the main battery (under the seat). I started to take apart the trunk to change the aux battery and then noticed that my aux battery was the wrong size (my suv uses the "small" aux battery instead of the "big" one). I was due to change them anyway.

Knock on wood, after traveling a couple of hunded kms, the problem hasn't come back. Was the culprit the old battery (10 year sold) or a possible bad sensor connection? I can't tell, but so far so good... I'll update if the problem comes back. Thanks for the help.
 
I am 99% sure it is not the battery. I went through this and also the Battery Management system and changed the battery and it made no difference and when you think about it, as longs as the battery will start the car then everything gets full voltage and current from the alternator when the engine is running. You can test this by starting the engine and keep it running and disconnect the battery. I think the battery thing is an old wives tale frankly. Good luck and I hope it fixes it.
 
As a matter of interest, garages here (France) often say it is the battery, change it for a vast profit and five minutes work, and it seems better. Usually this has nothing to do with the actual battery but the connections which can loosen over time or get crud on them. By changing the battery the connectors are cleaned and tightened. Voila!
 
Ok quick update. I still had the same issues after changing the batteries and the abs wheel sensor. It turned out to be a faulty wheel bearing. When I pulled out the wheel bearing it was extremely rusty and I guess the magnetic strip in the bearing was shot. Thanks everyone for the help.
 
Ok quick update. I still had the same issues after changing the batteries and the abs wheel sensor. It turned out to be a faulty wheel bearing. When I pulled out the wheel bearing it was extremely rusty and I guess the magnetic strip in the bearing was shot. Thanks everyone for the help.
Glad it is fixed and you probably fixed the right thing.
It is never the battery and the only sure-fire wayt to know if it is the reluctor or not is to clear all codes, switch on the ignition and see if there is a warning light. If so, it is the sensor and more than likely the sensor connection since the sensors are bombproof. If there is no light and it comes on when you move, it is the reluctor signal - due to rust usually.
The ECU has no way of knowing until the car moves and it expects a signal since it is getting one from the other three sensors.
If you don't clear codes first, the ECU can base its decision on stored values.
I keep repeating this because it took me a long time to work out why I was being conned by garages..
 
I have a a similar issue . Right abs fault comes on , active reading shows zero wheel speed - signal implausible

I have replaced the whole hub, new Bosch abs sensor but error returns after clearing it on xentry once the vehicle moves

The only culprit i can think is the plug that the abs sensor plugs into on the body of the car

I've been told, Bosch sensors are not OEM, you MUST use OEM only as the car won't accept after market, it's this true?
 
I used a Febi wheel sensor when I replaced mine, works perfectly so you don’t need to buy OEM.
Can you swap the sensors over to eliminate it, I did and it proved the sensor was ok, the fault on mine was a magnetic wheel bearing that packed up.
 
I have a a similar issue . Right abs fault comes on , active reading shows zero wheel speed - signal implausible

I have replaced the whole hub, new Bosch abs sensor but error returns after clearing it on xentry once the vehicle moves

The only culprit i can think is the plug that the abs sensor plugs into on the body of the car

I've been told, Bosch sensors are not OEM, you MUST use OEM only as the car won't accept after market, it's this true?
No not true.
It is the sensor plug either at fault or the plus is not seated properly or dirty
 
I have a a similar issue . Right abs fault comes on , active reading shows zero wheel speed - signal implausible

I have replaced the whole hub, new Bosch abs sensor but error returns after clearing it on xentry once the vehicle moves

The only culprit i can think is the plug that the abs sensor plugs into on the body of the car

I've been told, Bosch sensors are not OEM, you MUST use OEM only as the car won't accept after market, it's this true?
My S204 was quite happy with a genuine MB sensor on the NSF and a Delphi on the OSF
 

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