KeithParsons

Good Sunday morning. I am the owner of a 2005 W211 CDI. I love the mileage and the car in general. I am chasing a problem with the cruise control that i thought i had figured out, but unfortunately do not.

A little background on the problem is the cruise control does not work. I also have an ABS dash light, as well as the information cluster saying, "ESP, ABS, and Brake".
I bought the iCarsoft MB scanner and trouble shot it to the right rear speed sensor. I purchased one from ebay and swapped it out, but unfortunately it didn't correct the problem. Suspecting that the ebay part was the problem, i went directly to the Mercedes dealer and purchased a Wheel speed sensor from them. Installed it, and still had the same problem.

I got the pin out for the SBC system and checked (and had) continuity between the ABS pump and the right rear speed sensor. I then suspected that the ABS SBC pump was the problem. I purchased a used ABS pump and new wheel speed sensor from ebay and installed it in the car today. Everything went together easy enough, but when i took the car off the lift and got above 10 (or so)MPH, the abs light came back on. I checked the code, and again have the same right rear wheel speed sensor code!

At this point, i am lost. I was thinking that the ABS pump must be shorting the wheel speed sensor, but apparently i am missing something that is located between the right rear wheel and the abs pump. My question is what am i missing and where is it located!! an help would be appreciated!!

Paulmurphy

Probably the magnet ring on the drive shaft, that's what the sensor reads from. That part is avail separately, the steel band gets corroded and causes issues with the magnet band.

KeithParsons

I believe that magnetic ring is called a reluctor ring. I also at one point considered that to be the problem. But there is another part to this mystery. During my troubleshooting thinking that it was a wheel speed sensor, I swapped the left rear wheel speed sensor to the right rear position. The fault still appeared for the wheel speed sensor on the right, and also one on the left now because it was disconnected. The interesting part about it is when I reconnected the wheel speed sensor to the position on the left it no longer work. Something in the Circuit for the right rear wheel speed sensor shorted the sensor wire that goes to the wheel hub. Is this possible from The reluctor Ring?
I have considered running two new wires from the ABS SBC pump directly to the right rear wheel speed sensor harness.
but I was unsure if there is something in between the ABS pump in the rear wheel speed sensor that I am unaware of.
also, could the problem be past the ABS SBC pump, and actually be a problem in the electronic stability program unit?

Paulmurphy

Reluctor ring won't cause a short, it's purely a magnetic field think star or a decent diagnostics reader is what's needed

KeithParsons

Looking at a simple flow chart of the ABS system, it appears the signal from all 4 wheel speed sensors goes from each wheel to the ABS pump, then to the ESP module (located near fuse panel under the hood).
Could this problem be coming from the ESP module? Or am I missing something that is located between the sensor wire connector in the wheel arch and the ABS SBC pump?
open to suggestions!

VII

As you now learned ABS sensors are delicate (You cannot measure them with a multi meter because the current will burn it) but a short in the wiring would not ruin a sensor (Short = 0V between connectors no current in sensor).
As you also now know no ABS/ESP = no cruise control

It might be that the module is defective and is burning your sensors, but I would also make sure that the magnetic ring and it's clearance are good (the distance between the ring and the sensor is critical) before pursuing that more expensive option.

KeithParsons

Absolutely, I continued my trouble shooting this past weekend, as well as spoke with a few friends with more electronic experience than my own. They also believe the problem is in the ESP module. The thought they had was that inside the ESP module in a failed diode that is allowing current to flow down the sensor wiring. (This theory is not confirned, but is plausible). The diode should keep current going in the direction of the ESP module, and not allow current to go to the sensor.
Before going down that road, I wanted to check the wiring between the ABS pump and the rear right sensor connector in the wheel well. I bypassed the car's wiring, and used 2 new wires from the connector to the ABS pump. The results were the same. Still has a code for the rear right sensor.
I made the decision last night to purchase a used ESP module.
I purchased the same part number, with the same software date or version(?).
I'm keeping my fingers crossed this will be "plug and play".
I have a decent handheld MB specific code reader, but not a laptop with STAR.
I have read on the forums that as long as the software and version are the same, no STAR is needed.

KeithParsons

I had an unrelated issue arise from my w211. I trouble shot it to the "Central gateway" located under the steering wheel. I found crusty corrosion on the circuit board that was causing all sorts of codes related to the CAN-bus.
Does anyone know if the central gateway could cause issues with the sbc, abs, and esp? Is it part of the same circuit?
I've learned to live with no cruise control and a few codes on my dash, but if this is potentially the culprit, I want to fix the problem. Just hate shelling out the $$ for wheel speed sensors only to short them out.

ot1

to troubleshoot your cruise control problem you need an O-scope because your standard digital meter is not fast enough to see the pulses coming from the wheel sensor, and a Star diagnostic too.

Since the CGW is not connected directly to the wheel sensor it couldn't burn out a wheel sensor. Did you measure any voltage on the wheel sensor wires at the wheel sensor with the engine running? Did you look carefully at the pins on the right wheel sensor socket? Maybe it physically damaged the left sensor pins.

KeithParsons

The cruise control/right rear wheel speed sensor/ abs/ esp/ transmission problem is on-going for almost a year and a half.
I describe it like that because when I use the MB2 icarsoft scan tool, i get right rear wheel speed sensor faults on the reading for the transmission, the sbc, and the esp.

I have tried so so many different things to troubleshoot this and so far nothing has worked.
what's been tried:
1. replaced wheel speed sensor on rear right.
2. Replaced ESP control module.
3. Replaced reluctor ring on right rear axle.
4. Replaced SBC ABS pump.
5. Checked harness from ABS to right rear wheel speed sensor.
6 swapped left rear for right rear wheel speed sensor.

every attempted item I've changed on the car has made no difference in the symptom. Additionally, I have electrically damaged each wheel speed sensor that has been replaced while replacing the esp, abs, and reluctor ring.
When I say electrically damaged, I'm not sure if they are open or shorted, but I say damaged because once I have tried something new, the wheel speed sensor cant be used as a spare. While attempting to switch the left for the right rear, upon returning them to their original position, the left no longer worked and had to be replaced. This has made all sensors tried useless after the attempt.

VII

Sorry to hear you've had such a hard time with this.

If you are burning sensors there is current flowing through them because of voltage applied to them either by the control unit, wiring or induction.
Have you replaced the wiring ?

KeithParsons

I have not replaced the harness. But I did cut the two wires going to the right rear wheel speed sensor at the SBC ABS pump, and spliced in 2 new wires from there to the right rear wheel Arch where the connector is. Unfortunately, still seeing the same result.

VII

Wire diagram attached:
L6/1 Left front rpm sensor
L6/2 Right Front
L6/3 Left Rear
L6/4 Right Rear

If you have replaced the SBC control unit and different wiring with no change I would do the next:
1. Check SBC ground points and connector
2. Run a shielded cable (ground it of course) to a new sensor (Outside the car)
3. Connect a good sensor
4. With appropriate diagnostics equipment got to actual value for the sensor
5. Manually run a magnetic seal (the type used in the front hub)
6. See if the pulses are seen

At this point I would think you have something emitting a significant magnetic field that is inducing current in the wiring and burning the sensors.