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On a 2006 ML320 CDI have fault ABS/ESP inoperative (and also TPS as well which I assume is going out in sympathy)
I read the codes and got 5122(left rear speed sensor - check wheel bearings) , and 7270 (implausible values from rpm sensors - rear axle)
Have changed the rear left ABS sensor but code is still on. Have tried to clear and still on
nearly 3 years ago the ABS/ESP on this car had errors (which were the control unit motor brushes - thank majdundee) and it had the control module and pump motor swapped and all has been good til now
There is not noticeable noise or play in the wheel bearing it drives true etc
I have seen on other forums that this code has appeared after wheel bearings replaced but not the case here
Could this be an open circuit to the sensor (broken wire in harness?) the car has about 290,000km on it
I have played with the plug at both ends (sensor and control unit) and no change (in case a dirty conection)
is there a pinout diagram for the controller plug? and what values should I expect to sensor? or am I barking up the wrong tree...
I found the pinout (majdundee had sent it on a previous forum "ML 320 ABS Traction code 5967
I did resistance checks on rear circuits and wiring intact
I swapped sensors (had a spare from a 2010 ML350CDI) and still error occurred LHS rear (ie the hub is the only thing unchanged)
Put a small wire brush down the sensor hole and cleaned the rust off the hub - still had error
Put car together and drove it hard and braked hard on grass and engaged ABS 5 or 6 times - eventually ABS engaged and the errors on dash disappeared
The traction is also working fine now but interestingly the AUTEL scanner cannot erase codes 5122 and 7270 - but display on car has dropped the abs/esp lights and warning
All I can think is the cleaning of the hubs got it sorted (ATM)
Also had low voltage to control unit as a stored error (car had not been used for about 2 weeks)
Anyway all clear ATM, I will drive the car more commonly next few days and see if it comes back
Understand that a vehicle is unable to diagnose a faulty wheel bearing. That is why it is suggested that you check the wheel bearing.
Therefore, the replacement of the sensor did not clear the code, which means the problem is elsewhere.
You must take the car to an alignment shop where all 4 wheels can be suspended and run in drive. But this procedure must be followed prior to running in drive.
Thanks for that - I do have access to a lift (and indeed I did run it on the lift with all 4 wheels up - did a live data check - it read all 4 wheel speed. - it did engage ESP as it normally does in this scenario BUT obviously I did not have it in Dyno mode - I might have access to the lift in a few days and will give it a go
Could you please give me the heading for thread where "rudeney" post is?
The only logic I could get to the sensor thinking the wheel bearing was going is that the intensity (not the frequency) of the voltage (ac) was varying thinking that the distance form the hall sensor to the magnet was changing - play in bearing - given that there is no play in the wheel I then cleaned the hub as I thought possibly something alien on the hub could also do this.
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