I have a 98 Mystique auto w/2.5 Liter (daughters car). I have been battling a VSS error for several months. (I have researched all of the related posts on this forum). The problem started manifesting itself with an occasional lurch on the highway. My daughter told me this several times over several months, but when I drove the car it never did it. The CEL light then came on, when I checked it there was a vehicle speed sensor error code. I had the VSS replaced and the code came back a month later. I then started paying attention to the indicated vehicle speed coming out of the computer (I use Autotap software on my laptop) and noticed that the speed reading was sometimes wrong. The speed would indicate 0 to 60 mph when the car was running in park, and vary all over the board when driving. The actual vehicle speedometer ALWAYS reads correctly, sometimes not agreeing with the indicated speed from the ecm. I once again replaced the VSS. This once again did not fix the problem. I checked all of the grounds and battery cables. Indicated voltage on the ecm and my voltmeter on the battery agree and are stable around 13.8 when the vehicle is running, so I think I have ruled out that issue. My next thought was either a bad connection or bad wiring between the sensor and the ecm. (When I looked into the wiring on this car I was shocked to see very deteriorated insulation on many of the wires). Since the ecm seems to see a signal when the speedo doesn't, I suspected some sort of interference getting into the wire from the sensor to the ecm, so I cut the wire at the sensor, found the correct wire at the ecm connecter, and spliced a coax in between to replace the stock wiring, grounding the shield at both ends. (I always solder and heat shrink all connections) Other than the speedo not working, nothing changed. That should have ruled out wiring. Apparently the speedo splices off in the loom in the piece I bypassed. I hooked the factory wire back up at the ecm end and the speedo started working again. I then cut the wire again at the ecm so there was absolutely no feed going in and of course the speedo stopped working again and the computer no longer read vehicle speed, but the random output of 0 to 60 mph when in park persists, even with no wiring hooked up to the input to the ecm. My last guess is that the ecm itself has a problem in the circuit that converts the pulses from the VSS to whatever signal it reads, maybe an analog to digital converter of some sort. Unless someone on this forum has another idea, I am going to try to replace the ecm. Once again, the vehicle speedo has always read correctly, never jumping around as the speed indicated as read by Autotap from the ecm. It does appear to have the problem mainly when cold. Obviously the transmission shifts very poorly while the ecm indicates the incorrect speed and shifts properly when the ecm indicated speed agrees with the speedo. Did I miss anything? Any other ideas?
Thanks,
Dave
Thanks,
Dave