I noticed my Wife's '03 Neon SXT felt like it was dropping in and out of OD while driving the other day. After connecting a scanner to it and driving a while I realized it's really the TC locking and unlocking. I also noticed that the speedo jumps around whenever the TC unlocks. When the speedo stabilizes, the TC locks again.

I can make it happen by accelerating slightly and driving over a rough stretch of road. The bumps seem to trigger the problem. On a smooth surface everything works normally. It seems to be more sensitive to vibration when it's cold than when it's at running tempertaure.

Running the scanner in monitor mode while driving revealed that the VSS speed goes randomly low at the same time the speedo jumps and the TC unlocks.

The scanner pulled a P0700 code but nothing else.

I haven't dug into it any further yet but I'm guessing this is probably a flaky connection on the speed sensor.

Anyone know for sure if this is just a bad connection or a bad speed sensor, or something else?

Thanks!

 

Might be a bad connection since the 700 is the only code. It doesn't cost anything to check the connections, so it would be a good place to start! Might get some of that contact cleaner too and spray the connectors down inside while you are checking them.

 

Okay, I just disconnected the output speed sensor, unplugged it and spritzed a little contact cleaner on the pins. Then connected-disconnected-reconnected a couple times.

I took the thing for a quick test drive and everything worked normally.

At this point I figure I've either corrected the problem by cleaning the contacts, or there's a broken wire that's temporarily made contact again after moving the cable around.

I'm gonna open it back up and put a little dielectric grease in the connecter and leave it for a while. If the problem doesn't come back, I guess I'll have to call it fixed.

 

They are weird sometimes. My CEL light has come on about 8 times since I've had it (~18 months). Two times, it was something that actually needed to be fixed. I'd call it fixed if the wiring ends up looking good.

 

The wiring "looks" fine.

Years ago we had a Geo Metro Convertable that had a break in the low beam power circuit that caused the left headlight to be dim. The break turned out to be in the middle of a completely wrapped and protected harness under the left front fender.

Clearly a manufacturing defect in the wire itself, but it was enough to make me never fully trust a factory harness again.

Thanks for the response!