What is the rear wheel speed sensor?

Maverickxeo

Registered Member
Original poster
Jan 25, 2021
40
Alberta, Canada
On my 04 Envoy, I've been getting a C0055 code on my Bosch scan tool. It says the MIL is requested - but it has NEVER tripped a light. I don't believe I have any other symptoms (though I may be mistaken - it's had this code since I bought the vehicle).

I decided to probe further - using my scan tool (and under the ABS PIDs), I checked the FR and FL wheel speed and both are equal and accurate to the speedo while driving. The rear sensor always shows 0KM/hour. I am assuming this is not normal?

I was looking on the forums and I've found a lot of information pointing toward the rear prop speed sensor (or wiring) on the passenger side rear of the transfer case - but not the actual rear wheel speed sensor (I'm assuming there is one on the diff somewhere? I haven't actually looked yet). Is this sensor on the transfercase the correct 'cause' of the code?
 

TJBaker57

Guru
Aug 16, 2015
2,000
Colorado
On my 04 Envoy, I've been getting a C0055 code on my Bosch scan tool. It says the MIL is requested - but it has NEVER tripped a light. I don't believe I have any other symptoms (though I may be mistaken - it's had this code since I bought the vehicle).

I decided to probe further - using my scan tool (and under the ABS PIDs), I checked the FR and FL wheel speed and both are equal and accurate to the speedo while driving. The rear sensor always shows 0KM/hour. I am assuming this is not normal?

I was looking on the forums and I've found a lot of information pointing toward the rear prop speed sensor (or wiring) on the passenger side rear of the transfer case - but not the actual rear wheel speed sensor (I'm assuming there is one on the diff somewhere? I haven't actually looked yet). Is this sensor on the transfercase the correct 'cause' of the code?


Well you got me here as I cannot remember what year they began using two actual rear wheel speed sensors as opposed to the earlier models where they had no rear wheel speed sensors and instead used the vehicle speed sensor on the transfer case.

Either way it is not normal to ahow 0 Kmh for the rear wheel speed(s)
 

Maverickxeo

Registered Member
Original poster
Jan 25, 2021
40
Alberta, Canada
Well you got me here as I cannot remember what year they began using two actual rear wheel speed sensors as opposed to the earlier models where they had no rear wheel speed sensors and instead used the vehicle speed sensor on the transfer case.

Either way it is not normal to ahow 0 Kmh for the rear wheel speed(s)

I imagine mine would have the separate wheel sensor as the speedometer works, right?
 

TJBaker57

Guru
Aug 16, 2015
2,000
Colorado
For a little more info,,,

I believe you have the 3 sensor abs system that doesn't use separate rear wheel speed sensors. Your transfer case will likely have 3 speed sensors on it. One each for the front and the rear propshafts that are wired to the TCCM (transfer case control module). And the third is the vehicle speed sensor that is wired to the PCM. From the PCM there is a dedicated wire going to the EBCM which is a speed signal. Maybe this wire is compromised in your vehicle.

Screenshot_20211122-164933.png
 
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Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,859
Ottawa, ON
Well you got me here as I cannot remember what year they began using two actual rear wheel speed sensors as opposed to the earlier models where they had no rear wheel speed sensors and instead used the vehicle speed sensor on the transfer case.
2006 was the first year.

If there was an issue with the rear speed signal, you would have no speedo reading and the transmission would not shift. Saw this on a truck that the owner accidentally swapped the front and rear sensor connectors.

This thread has some info but unfortunately the OP never came back to report results.
 

TJBaker57

Guru
Aug 16, 2015
2,000
Colorado
there was an issue with the rear speed signal, you would have no speedo reading and the transmission would not shift. Saw this on a truck that the owner accidentally swapped the front and rear sensor connectors.

But the issue can still be between the PCM which reads the speed sensor directly and the EBCM which receives the speed signal that is sent from the PCM to the EBCM by a direct wire carrying a vss signal.
 
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Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,859
Ottawa, ON
True. That can help pinpoint where the problem is. However wouldn't you get a P code for a missing speed signal if it was a problem between the sensor and the PCM? That other thread didn't mention a P code.
 

TJBaker57

Guru
Aug 16, 2015
2,000
Colorado
However wouldn't you get a P code for a missing speed signal if it was a problem between the sensor and the PCM?

I would think so, yes.

But if I am reading this thread correctly there is no P-code present and the speedometer works fine so the sensor, sensor wiring, and PCM reading of the sensor is OK. The OP has read a C-code (C0055) from the EBCM that indicates there is no vss signal at the EBCM for the rear wheels. That VSS signal is sent from the PCM to the EBCM via a direct hardwired circuit. Thus the issue appears to be between the PCM and the EBCM, either a wiring fault, a failure of the PCM to send the signal, or a failure at the EBCM in receiving the signal.

Someone shoot me down :wink:
 
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Chickenhawk

Hobbyist
Dec 6, 2011
716
A broken wire at the wheel speed sensor would also cause a 4WD trouble code. This is common because the wiring is in a vulnerable spot under the truck. (Ask me how I know.)

A simple way to eliminate a broken wire or bad sensor is to shift into A4WD. If it starts to crow-hop right away, especially in parking lots and at slow speeds, the sensor is bad or the wires are broken somewhere. (The transfer case thinks the rear wheels are slipping and engages the front driveshaft when it shouldn't.)

If operation of the 4WD system in A4WD is normal and there are no 4WD trouble codes, then the sensor is fine and the wiring as far as the TCCM is good.
 

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