W164 rear wheel speed sensors wiring

[MercOffroad]

Good day everyone

I have a 2007 ML500 and ran into a little problem. After doing some off-roading the dashboard suddenly went haywire after going over a bump. I have brake, ABS, ESP and a check engine warning light. Car is running perfectly fine otherwise. No engine or transmission issues and no limp mode either.

After connecting the trusty iCarsoft MB OBD it looks like the issue is with both rear wheel speed sensors. More than one module's error codes specifically mentions that both rear wheel speed sensors are not available on the can bus. I assume it might be wiring related since it's a tad bit unlikely that both will fail at the same time. I don't have any rear SAM issues otherwise all rear lights and everything else seems to be working.

I don't have much experience with DIY'ing the W164 so I'm looking for some advice. I already jacked up the car and removed the plastic covers on the driver's side (RHD car) and I don't see an obvious path for the wires so if someone can point me in the right direction it would be very appreciated. I'll also post the specific error codes from the icarsoft if needed.

Regards,

 

[MercOffroad]

OK so after fiddling around a bit more I decided to plug in the Icarsoft MB again and I noticed that all the error codes specifically points towards n47-5 esp control unit... Both rear wheel speed sensor values are not available on the canbus. I jacked up the car again, removed the covers and checked all the visible wiring front to back. I can't for the life of me find anything with any noticeable damage whatsoever. I also checked under the bonnet and removed the fuse box cover in the engine compartment. Fuses checked out fine, also checked all the wiring going towards the fuse box as well as wiring going into the ABS unit. Nothing seems damaged, however it is difficult to check everything without removing components.

One thing I would like to know, does the rear wheel speed sensors plug directly into the ABS unit or does it go somewhere else first? Perhaps I can resolve the issue by process of elimination.

Regards,

 

[Magic1973]

I noticed you said no rear sam problem, have you checked in the boot at the rear sam (rhs rear panel) for signs of water ingress? Or just no evidence on reader? Do u have any other (current or historical) errors for interior modules for example centre ceiling cluster, tailgate lock. If you have multiple sensor failure for items connected to rear sam be suspicious. Very common failure. Even the replacement i bought had non critical errors on it. Look for obvious burning on the board (have to remove plastic case). Also track the cables back to any junction plugs- i had green corrosion in one of mine between engine sensors and front sam/ecu. Good luck

 

[MercOffroad]

I noticed you said no rear sam problem, have you checked in the boot at the rear sam (rhs rear panel) for signs of water ingress? Or just no evidence on reader? Do u have any other (current or historical) errors for interior modules for example centre ceiling cluster, tailgate lock. If you have multiple sensor failure for items connected to rear sam be suspicious. Very common failure. Even the replacement i bought had non critical errors on it. Look for obvious burning on the board (have to remove plastic case). Also track the cables back to any junction plugs- i had green corrosion in one of mine between engine sensors and front sam/ecu. Good luck

Hi Thanks for your message. There is no water ingress at all in the rear sam. I don't see any other system failures on the reader for items connected to the rear sam.
Does the rear wheel speed sensors wiring run to the rear sam first, or does it run straight through to the front and is connected to the ABS system? Regards,

 

[Magic1973]

That I don’t know- mine errored on worn brake pads so there are brake sensors connected to it- whether the speed sensors are i am not sure, again though follow wiring back to any junction plugs on the way to sensors and check pins for corrosion. It seems a common theme on the older ones at least. Mine is a 55 plate and i found water damage in 2 plugs under engine bay fusebox that looked great till i separated, plus the rear sam. Front sam is pretty out of the way and mine was clean/dry no evidence of issues.