Can't resolve vehicle speed sensor implausible signal (P0501)

[BaseDrifter]

A few months ago I started getting a P0501 (vehicle speed sensor implausible signal) code. At first the code would show up in VCDS but with no corresponding CEL and the speedometer still worked. A month ago the CEL started to come on but the speedometer still worked. As of two weeks ago the speedometer would only work intermittently along with the code and CEL.

I started by replacing the speed sensor itself with no change in the symptoms.

Today I replaced the magnetic ring inside the transmission and the problem is still unresolved. Still getting P0501, still have a CEL, speedometer still works intermittently. The magnetic ring I pulled off my car did not appear to be damaged. I've searched and searched and everyone points to the magnetic ring being the culprit.

I would greatly appreciate any advice on where to start poking around next. Gotta be the wiring??

[zillarob]

iirc, vss goes to cluster and cluster kicks it out to the ecu. If cluster is hoaky, could mess with the ecu signal.
Been a while since I looked at the diagrams though.

[EuroxS4]

If you replaced the sensor with the correct part and are still having and issue.Check the connector and the pins inside make sure you have a good contact.Other than that your gonna have to maybe take a look at wiring possibly trace wires and make sure you dont have a broken wire anywhere.

[hanzy]

Have you scanned the cluster for DTC's?

Might not hurt to take a look at some of the MVB in the cluster, see if anything looks out of place.

[ianwpb]

When the Speedometer stops working does your fuel gauge move erratically too?

[M-Hood]

VSS signal goes to the cruise control unit before it goes to anything else. That might be where your issue is at.

[BaseDrifter]

I've scanned the cluster, no codes. No codes on any of the other modules. Fuel gauge seems to be working correctly.

The magnetic ring I ordered was 012-409-182-C. The one I pulled off the car was 012-409-182-A. The only difference I noticed was in the lack of a plastic locating notch on the replacement piece. It ended up locking into place with one of the side clips. ECS also says the C version supersedes the A version.

Mike, my CC hasn't worked since I bought the car. I did a hardware check and it all works so my problem is electronic. I'll start with the CC unit and see what I find. Thanks for the suggestion. Time to dive back into the wiring diagrams.

[BaseDrifter]

Since I won't have access to the garage for a few more days I decided to trace the VSS circuit in preparation.

From the VSS the signal passes through a brown/red wire into the instrument cluster through pin 23 on the blue connector. After going through the cluster processor/speedometer it passes out through a white/blue wire on pin 6 of the yellow cluster plug into pin 20 of the ECU. Since my car was made before 8/97, the same signal from pin 6 on the yellow cluster plug goes to the cruise control module, pin 9.

Since my cluster doesn't seem to be receiving the signal I'm going to start with the wiring from the VSS to the cluster and see if there are any problems. Then I'll dig into the CC module.

[BaseDrifter]

Oh glorious day!!! I do believe I found the source of my speedometer woes.

I started by checking continuity of the wire going from the VSS to the cluster, all was well. Next step was to check the connections within the cluster to see if the signal was passing from the blue plug to the yellow plug. I pulled out the cluster.

All looks fine and dandy...



Wait a minute..whats that?!?



Cheeky bastard!! :D Could that possibly be the pin for the VSS? Yes it is, T26/6, blue/white wire that goes out to the CC module and ECU.

Now, is it merely a coincidence that the green paint you see there is right next to my bent pin? That green paint is from when the pick n pull when I pulled the cluster. The only thing I can imagine is that the paint pen slightly bent that pin. All was well for a number of months until the last time I pulled the cluster when I did my big rewire. It must have got shoved over when I plugged in the yellow plug last time.

I bent it back into place and made sure it was as straight as could be with a magnifying glass.

What I can't figure out is what pin it was shorted to. It was touching the opposite pin, #22. However I couldn't see pin 22 in the wiring diagram for the cluster processor. The wire is brown, so maybe it's just a ground.

I haven't driven the car yet since I've got the bumper off for realignment while I replace the fog light hardware. Tomorrow I'll give it a run and hope for the best. I cleared the vehicle speed signal implausible code tonight for hopefully the last time.

So after months of having the CEL on and a speedometer that worked 1% of the time, $100 in parts, at least 15 hours of diagnosis/labor, the fix took 5 minutes...