My 2001 PT Cruiser was bucking and misfiring at random times and the speedometer was erratic and going nuts! It was so severe that when it happened it would throw me towards the steering wheel as if I’d ran into pole or something! It would then smooth out and run fine for a bit with the speedometer reading zero, and suddenly it did it again! My first thought was that it was a bad plug or plug wire, or perhaps the coil pack was going out.

I changed all of those but it didn’t fix the problem. I wasn’t getting any codes from the odometer check other than an oxygen sensor being inactive but I knew that wasn’t the cause. Next I purchased an OEM camshaft position sensor but that didn’t fix it either. I search the internet hoping to find the answer but I found that there were people having the same trouble and they didn’t know how to fix it either. There were a lot of “could be” suggestions and I tried a lot of them but nothing seemed to work.

I was beginning to think I had a intermitting short somewhere in the wiring harness that was going to be a nightmare to track down. I didn’t think much about the speedometer acting up during the misfires because I’d read that a lot of people who were having this problem experienced this strange effect on their gauges. A short in the wiring made sense but I hated the thought of trying to find it.

I decided to change the vehicle speed sensor (VSS) even though I wasn’t getting a code for it and no one had even suggested that it could be the cause. I thought it was a long shot because the speedometer did work most of the time until it started misfiring.

But that ended up being what was doing it. It was in fact the $54.00 vehicle speed sensor! I’m an old school mechanic and used to working on cars with distributor caps and rotary buttons. Cars with speedometer CABLES that had nothing to do with ignition timing. But with today’s cars I wouldn’t be surprised to find that the power windows had something to do with the gas cap!

From what I remember on the PT Cruisers the vehicle speed sensor has a 5 volt reference to it and it may been shorting to ground at times. If the 5 volts shorted to ground it would pull all the 5 volt sensors volts low to zero. And since the cam , crank , TPS , MAP and other sensors use the 5 volt feed it could have made the car do that. Some of the sensors would not kill the eng but the crank sensor would. Ron

One thing that really messes up PTs is a battery going south. They are very sensitive to voltage loss.