No speedometer, CEL, VSS code, and I'm at a loss...

[ZeroSignal]

The problem began with an intermittent speedometer on my 99 XLT (5.0L). It would work on and off at its own will. Eventually, the CEL came on and the code pointed to a faulty VSS.

I have replaced the output shaft speed sensor (on the transmission housing) and the sensor on top of the rear differential. Both sensors were Hall-effect magnetic pickups. According to the Haynes manual, I should have a gear driven sensor, but my truck has a Hall-effect sensor instead.

With both sensors replaced, I still have no speedometer and a CEL. It does not affect how the truck drives or how the transmission shifts.

I pulled the VSS connector and I'm reading 0.05VDC. According to the Haynes manual, I should be reading approximately 1.5VDC. I pulled the connector off the PCM and checked continuity of the wires from the PCM connector to the VSS connector. Continuity checks were good on both wires. On the VSS ground wire I have less than 0.2ohm to ground, which is also good.

So, with a wiring problem ruled out, but still no voltage at the VSS connector, do I have a bad PCM?

 

[2000StreetRod]

VSS source

I think your 1999 is like my 2000. The VSS signal to the PCM comes from the 4WABS module.

Rear axle sensor > 4WABS > PCM, speedometer, cruise control, radio

Does your cruise control work? If so, then there's nothing wrong with the rear axle sensor, or the wiring from it to the 4WABS, or the output of the 4WABS.

 

[ZeroSignal]

Thanks for posting the schematic. It helps clarify why my wiring colors were different than what the Haynes manual had listed.

The ABS light came on yesterday after all of my troubleshooting efforts.

So now, symptoms include: No speedometer, with CEL and ABS lights illuminated. Cruise Control hasn't worked on this truck in a LONG time, due to dry-rotted and cracked switch pods on the steering wheel. I don't drive the truck on long road trips, so lack of cruise control was never a high priority to fix.

Is there another way to troubleshoot the 4WABS module w/o using cruise control to verify its operation?

 

[boominXplorer]

You can clean and check the connection but that is about all you can do without a scan tool. It should be on the drivers frame rail in front of the fuel tank

 

[ZeroSignal]

I found the module... driver's side just behind the battery.

I'll pull the connector and clean everything up and see if cleaning and reseating the connector helps.

I found a few on eBay and prices range from $40 to $500 for the control module and pump assembly.

 

[2000StreetRod]

Message center?

Do you have a message center? The message center uses the VSS to calculate fuel economy. Also, the radio uses the VSS to increase the volume as vehicle speed increases. That's probably not a reliable way to test the signal.

Since you have an ABS fault I suggest that you try to read the code and post it. The code will start with C for chassis. It may take a special code reader to read it. You may just have a faulty front wheel sensor.