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I have a 2000 Pontiac Sunfire. The transmission ...

Sent to Car Experts August 21, 2006 12:19 a.m.

I have a 2000 Pontiac Sunfire. The transmission is shifting between drive and overdrive while on the hiway. Also the speedometer is bouncing all over the place, from 65 down to 40 and then back up again. Whats the problem?

Optional Information:
2000 Pontiac Sunfire 2.2

Already Tried:
tuneup, computer code check negative

Customer (name blocked for privacy)

Status: Closed Value: $30

Answer
August 21, 2006 12:43 a.m. (23 minutes and 48 seconds later)

ACCEPTED

This sounds like a problem in the VSS (Vehicle Speed Sensor) circuit. The VSS sensor is used to inform the instrument cluster of the vehicle speed, but also to tell the PCM (Powertrain Control Module) what the vheicle speed is, in order to promote transmisison shifting, and other engine performance calculations. In order to verify a failure in this circuit, which can lead to the repair/replacement of the VSS, the wiring to PCM, or the PCM itself; the PCM data stream for the VSS has to be viewed using a factory level bidirectional scanner to watch the vehicle speed at the time the problem is occuring. If it fluctuates along with the speedometer, the VSS signal has to be verified at the sensor with a lab scope. If the scope shows the same fluctuation, the VSS may be faulty.

-Rip

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RIP -- Lead Technician -- 100% Positive Feedback on 2106 Car Accepts
A.S.E. Master Technician, Advanced Level, Smog - European, Domestic, & Asian -- Car Category Mentor

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