Speedo Reads 0 and I Only Have 1st Gear - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 11-10-2009, 08:10 PM   #1
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Default Speedo Reads 0 and I Only Have 1st Gear

This happened suddenly when driving on highway speedo started reading about 30 mph less than it should be. Exited highway and car stalls. Restarts no problem but now Speedo reads 0 and only 1st gear. Next day I scanned codes and got (From newest to oldest) P0502(Low Vehicle Sensor Circuit), P0502 and P0705(Transaxle range sensor circuit malfunction). I take car for drive in parking lot with scanner still hooked up and car shifts to second, speedo is moving and scanner reads vehicle speed but speedo seems off by 5mph. I take out on road (car warmed up) and no speedo and only first gear. Scanner is reading car speed. I get back and park and check to see if PCM sees the different transaxle positions and it sees all of them. I moved the selector through all positions about 5 times to see if any were not seen correctly. No new codes set after driving about 10 minutes.

I am thinking that one or more is my problem:

1) PCM is bad
2) Wiring Problem
3) Bad VSS
4) Bad Neutral/Transaxle switch.


Any ideas?

I won't be able to get to it until Saturday but I think my first action will be a PCM swap as I have a spare.
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Old 11-10-2009, 10:49 PM   #2
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I seem to remember 95s having PCM problems.
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Old 11-11-2009, 10:15 AM   #3
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Def odd that both the PNP and VSS would puke at the same time. They may share a common ground. ???

The PCM'* in those years are the flakiest of all, but then...I've yet to see it fail in this type of manner.

Where to go from here? I'd look for any wiring or connections that appear bad. Maybe change the VSS/PNP with JY parts to keep costs low. They don't fail frequently and usually not at the same time.

shifting etc could be due to the pcm not being able to see what gear the car currently is in.
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Old 11-11-2009, 10:51 AM   #4
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Thanks guys. I'll swap PCM this weekend and go from there. I'll keep you updated.
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Old 11-14-2009, 05:03 PM   #5
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Swapped PCM and same problem. I did get codes real quick though which was P0502. PCM ruled out.

I change VSS and same problem and code. The old VSS looked to be a newer one not original but I could be wrong. So it is not the VSS.

Is there anything internal where the VSS goes that could cause this problem?

I believe the problem is a wiring issue. Anyone have a diagram of the wiring harness that goes to the VSS?
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Old 11-15-2009, 09:14 AM   #6
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I would back trace the harness some, I had a similar issue years back with one of my luminas, turns out the engine harness was slightly damaged from a wreck and the salt got into it and accelerated the degradation of it.
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Old 11-15-2009, 02:27 PM   #7
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I have seen a lot of issues with the VSS connector. Make sure that it is good. GM does make a pigtail harness for it if you need one.

All the VSS does is pick up a pulse from a reluctor (tone ring) on the differential. If the reluctor came off the diff, that would cause your problem.

If you have a volt meter, connect it to both wires @ the VSS connector and with the key on spin both wheels in a forward direction, you should see a pulse. If so, it'* not a problem with the reluctor or the sensor.
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Old 11-15-2009, 05:27 PM   #8
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Turns out to be a broken wire about 2 inches from the connector. My daughter will be taking to local mechanic to have that fixed as well as the leaking oil sender. I just can't get underneath. My next house will have a lift or I'll have one installed! Thanks everyone!!!
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Old 11-15-2009, 05:56 PM   #9
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That sounds like a easy enough fix. Hope that corrects the problem. Let us know.
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Old 11-15-2009, 09:38 PM   #10
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It will correct the problem. I used to stock that connector.
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