Speedometer acting erratically

**Bonjourmate** · 07-16-2012

First off, I tried searching around the forum to see if anyone has experienced a similar issue, but was unable to find anything that solved the problem. If this has been discussed before, please let me know.

The speedometer in my 2006 Grand Prix (3.8L V6 Supercharged) has been acting erratically for a while now. It'll fluctuate all over the place while driving (e.g., 70 to 30 to 50 to 10), which causes my cruise control to disengage and a gear shift. I've already had a local mechanic replace the VSS and the Gauge Cluster, but the issue is still going on.

Does anyone have any ideas about what else it could be? I really don't want to take it to GM, as they charge about five times per hour of what I can pay my local guy. However, if I can't figure out what needs to be replaced, I'm out of luck.

**Sven the Sexman** · 07-16-2012

My guess would be in the wiring between the PCM and the speed sensor if the sensor is new. The sensor has two wires twisted together to avoid electrical interference so if this wiring is damaged, the new wiring needs to be twisted together to restore the shielding. The other thing it could be although I have never seen it personally is the reluctor wheel in the trans that the speed sensor references.

**GMCustomerService** · 07-17-2012

Originally Posted by Bonjourmate

First off, I tried searching around the forum to see if anyone has experienced a similar issue, but was unable to find anything that solved the problem. If this has been discussed before, please let me know.

The speedometer in my 2006 Grand Prix (3.8L V6 Supercharged) has been acting erratically for a while now. It'll fluctuate all over the place while driving (e.g., 70 to 30 to 50 to 10), which causes my cruise control to disengage and a gear shift. I've already had a local mechanic replace the VSS and the Gauge Cluster, but the issue is still going on.

Does anyone have any ideas about what else it could be? I really don't want to take it to GM, as they charge about five times per hour of what I can pay my local guy. However, if I can't figure out what needs to be replaced, I'm out of luck.

Is this an intermittent issue or a regular occurrence?

I also suspect a wiring issue, possibly the wiring harness connections. This is just a suggestion, not a diagnosis. I encourage you to consult with a certified technician for an official diagnosis.

Please keep us posted.

Louis
GM Customer Service

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