If there is too much play in the wheel bearings the distance between the reluctor (the splines on the hub) and the ABS sensor can change as the wheel rotates, hits bumps, etc. The change in distance will change the voltage of the ABS signal which can produce a secondary signal which gets injected into the signal stream from the wheel sensors. If it gets too bad, the extra signal could, in theory, confuse, the 4-matic controller which derives its data from the ABS sensors.@Floobydust
The tyres are all the same size and are in good condition. I wish it were a case of bad tyres!
Your point about wheel bearings is interesting. I’m not sure if their condition or adjustment. Could you explain a bit more about that?
@tuttebenne I am hoping that @Real1shepherd can help me, as he has so many others!
Thanks for your replies.
I have conducted a code scan using the OBD port which shows no errors. I did not realise there was another way of reading error codes? I am following the procedure in the 4MATIC workshop manual which I have. I know that the error system is working correctly as I forgot to re-connect one of the speed sensors and it flashed the relevant code.Have you made the 4Matic brain itself render codes?
I reasoned that the brake light switch is working correctly as when I touch the brakes the 4MATIC function indicator goes dark.The 4Matics have their own brake light switch as well.
I have swapped the ABS unit for a spare one I have and this made no difference. I have also swapped out the 4MATIC unit and this too made no difference.We had this same problem before with the trouble light illuminating only at hwy speeds. Turned out to be a bad ABS unit.
That would be appreciated. I will PM you now.PM me with your email and I'll send you the bleeding method and how to get 4Matic codes.
attached is a PDF I scanned a few pages from a book I got years ago.
This is what I did, but using an external blinker rather than the light on the instrument cluster.Flooby,
On the test connector X92(by the battery), you short out Pins#1& #5 momentarily to get the 4Matic codes to blink on the dash trouble light. Shorting them out for more than two seconds erases previous codes.