Another symptom of an OSS problem is that the car will frequently die when coming to a stop if the PCM is not seeing a speed signal. The PCM drops the RPMs faster when the car is stopped than it does when the car is moving. That is because the power brakes and power steering puts a load on the engine as you are stopping. If the PCM drops the RPMs too fast with that load, the engine can die.
Speedometer bouncing and car bucking
- Thread starter shurur
- Start date
Mark to the rescue again.
I had same issue with the VSS on my 98. Also, with the broken VSS, my odometer wasn't working either.
In 94-98 cars, the odometer is driven by a stepper motor that is controlled by the speedometer. With no speed signal, neither will work. In 99+ cars, the odometer is in software. I am not sure if that software is in the PCM or in the instrument cluster.
Thanks.
The tach reads fine.
So since both tach and speedo use the OSS via the data+ signal (tan/org), I am leaning toward the speedo failing.
The speedo was intermittent; now speedo is dead.
[If the speedo is dead, then the idea that checking the pcm speed to the actual speedo to see whether the OSS sensor is bad is not a valid approach..and the pcm is looking at the actual speedo info coming from the cluster ecu as a feedback loop somehow..write-read-verify...I wonder whether data+ and data- are differential, simplex or full duplex (digital)..full duplex makes more sense, but the signal names seem to be differential]
When I get the cluster plugged back in..then get the battery hooked up, I will watch for the sweep and then run cluster diagnostics.
After I am quite sure it is the cluster, I may take it apart and check for cold solders before shipping it for repair.
In 2015, I soldered the cold soldered ribbon cables in the cluster and got the odometer running....I can't remember the speedo not working at that time...but it may not have worked. This may be the same problem all over again..dunno.
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Ok..connected everything up, minus the speedcal, and ran the instrument cluster diagnostics. Everthing looked good.
I set the odometer display to read speed and took her for a drive. All is working fine.
I did find a loose connector going to the airbag SRS module. The red tab was broken and it was pulled out about half way. I pulled it and did the dab of permatex trick, then reconnected it and let it dry. That module gets the same singke iso data signal as the datalink connector. Dunno.
The speedcal will go back in next.
If it works with the speedcal in then it was some connector or an intermittent problem that will show itself again. I will run the cluster diagnostics immediately at that point!!
I set the odometer display to read speed and took her for a drive. All is working fine.
I did find a loose connector going to the airbag SRS module. The red tab was broken and it was pulled out about half way. I pulled it and did the dab of permatex trick, then reconnected it and let it dry. That module gets the same singke iso data signal as the datalink connector. Dunno.
The speedcal will go back in next.
If it works with the speedcal in then it was some connector or an intermittent problem that will show itself again. I will run the cluster diagnostics immediately at that point!!
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