Help Needed - Rear Speed Sensor Wiring Leads to Nowhere. w/ PICS

[LoCascio_Inc]

1998 K2500 ECSB has had a code C0236 (missing rear speed sensor) since purchased.

I disassembled the wiring harness to look for a short and revealed that the wires from the rear speed sensor on the transfer case output terminated at another connector with a female to female adapter about 18" down the harness.

Connector A was plugged into the rear speed sensor. Connector B was bundled to the rest of the harness (appeared factory). I'd always assumed it was for a PTO or some option my truck never came with.

I'm confused about where to go from here. No other unplugged connectors appear to be anywhere in the area.

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[LoCascio_Inc]

Turns out this harness extension/adapter is to extend the connector for the rear VSS in 4x4 applications from the output sensor on the 4L80E transmission to the output sensor of the transfer case. I unplugged the harness from the transmission's output sensor and plugged it into connector B on the extension. Now the output sensor on the transfer case should be applying rear VSS signal as intended, but I'm still getting a C0236 (missing rear speed sensor). I think I have a short somewhere...

Does anyone know where the green and purple wires from the rear speed sensor lead to so I can check continuity? The ABS controller under the hood? Any advice on which pins to test from?

 

[9601216]

Turns out this harness extension/adapter is to extend the connector for the rear VSS in 4x4 applications from the output sensor on the 4L80E transmission to the output sensor of the transfer case. I unplugged the harness from the transmission's output sensor and plugged it into connector B on the extension. Now the output sensor on the transfer case should be applying rear VSS signal as intended, but I'm still getting a C0236 (missing rear speed sensor). I think I have a short somewhere...

Does anyone know where the green and purple wires from the rear speed sensor lead to so I can check continuity? The ABS controller under the hood? Any advice on which pins to test from?

Hi, the wires from rear vss go to your PCM connector C1, blue pin connector. Bee informed, that these wires are twisted between each other to reduce interference between the wires and are put in their own insulation with an extra shielding of aluminium tape and non isolated wire going together with them in their insulation:

- LT.GRN/BLK -> C1 pin 29 (Low signal)

- PPL/WHT -> C1 pin 30 (Hi signal)

 

[LoCascio_Inc]

Hi, the wires from rear vss go to your PCM connector C1, blue pin connector. Bee informed, that these wires are twisted between each other to reduce interference between the wires and are put in their own insulation with an extra shielding of aluminium tape and non isolated wire going together with them in their insulation:

- LT.GRN/BLK -> C1 pin 29 (Low signal)

- PPL/WHT -> C1 pin 30 (Hi signal)

Thank you!

Sorry if this is a rudimentary question but, what is the C1 designation?

 

[9601216]

Thank you!

Sorry if this is a rudimentary question but, what is the C1 designation?

At you PCM (called black box) you have 4 plug connectors C1 (Blue), C2 (Red), C3 (Grey), C4 (black).

Here are some pictures of your PCM under the hood & by it self, connectors that plug in to it, and here is a link to a web site, with pinouts of your connectors: https://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/pcm-connector-pin-outs-1998-1999-page-1

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[LoCascio_Inc]

Hi, the wires from rear vss go to your PCM connector C1, blue pin connector. Bee informed, that these wires are twisted between each other to reduce interference between the wires and are put in their own insulation with an extra shielding of aluminium tape and non isolated wire going together with them in their insulation:

- LT.GRN/BLK -> C1 pin 29 (Low signal)

- PPL/WHT -> C1 pin 30 (Hi signal)

I tested both wires for continuity and it turns out the purple/white wire has a break or short somewhere between the PCM and the sensor connector. Green/black wire tested fine. After pulling back some of the tape and split loom on the factory harness I can see what you're describing.

It seems like it may be easier and less invasive to re-wire the rear speed sensor with a new, separate length of harness and leave the old wires and insulation in the factory harness. Could the connector at the PCM be to blame?

Any other advice on the matter or how to best re-create a rear speed sensor wiring harness?

 

[LoCascio_Inc]

I went back and double checked my tests and it turns out both wires are showing continuity actually. At this point I'm stumped.

• Reluctor wheel is present inside of transfer case.
• Speed sensor is new and assumed to be functional.
• Wiring harness shows continuity from speed sensor connector to PCM connector.
• Clearing codes and leaving battery disconnected for 20min seems to nothing

Could the PCM be malfunctioning? Could the sensor be too far from the reluctor ring and not getting a proper reading? Is there another component that could be defective and trigger a code C0236?