VSS/ speedometer
 

Hello, hope someone can help me... I've read about others having the same problem as I have several times, but haven't seen anything other than to clean or replace the vss. My 98 4WD speedometer started jumping erratically and the transmission acts like it is in neutral if I'm going over about 20 mph. If I start from a stop, the transmission won't shift out of first gear. I did replace the vss (drivers side of the transfer case) before I read anything about just cleaning it.

I guess what I'm asking is, what is the next step? My ABS light has been on for a while and I ignored it, so I thought maybe there is a connection, but then I read that some people said the wheel speed sensors have nothing to do with the speedometer. What else could cause the speedo and trans to act that way? Is the next point in the line to replace the PCM? Anyone who has had this problem and had to do something more than replace the VSS, how did you solve the problem? Any help would be very much appreciated.

Have you tried logging vehicle speed? If so, does it have any inconsistency to what's displayed on the gauges? Scan the car for DTC's and check if the VSS signal is erratic also. You will need the VCM scanner for that. When I purchased my 96 blazer it exhibited the same problem with the vehicle speed sensor and it turned out to be a bad stepper motor in the gauge cluster.

The first time I checked the codes with an OBDII scanner, I had a PO503 code, but I haven't had it show back up since. That's "VSS circuit range performance". The rest of the gauges seem to be working fine, I haven't noticed anything wrong. Thanks for your help.

I was able to "coax" the speedometer and transmission to work, I would let off the accelerator when it was ready to shift to second, and the speedometer would jump around, then the trans shifts and it drives fine. I don't know where to look next.

Anyone ever find a cure for this problem? I'm having the same issue

If replacing the sensor did not cure the problem, the next thing I would check is the reluctor ring in the back of the transfer case (if 4wd) or transmission (if 2wd) for debris between the notches in the ring. If metal flakes build up in the notches, it will lead to inaccurate readings.

If that checks out, then you'll have to test the wiring from the sensor back to the PCM. P0502 is posted in the Tech section and has the applicable wiring diagram.

Ok thanks ill start with the sensor then. It just started doing this yesterday so just trying to get a good diagnoses to the problem