Erratic speedo on 2005 Impala fix

One of our cab drivers brought in his car with the complaint of erratic speedo and transmission not shifting properly this morning. Since we have lots of speedo clusters from scrapped cabs, we switched out the cluster to eliminate that...still had the issue, then we changed the speed sensor, it had a bunch of crud and metal filings on it ( recently rebuilt tranny) so we thought this might be the problem, nope....then we replaced the two wires running from the sensor back to the PCM, thinking might be some sort of bad wire (after ohm testing the the two wires)

This turned out to be the fix, which was good, we were getting closer to the PCM which was a non feasible repair.

Put this out there for anyone else who runs into this issue, it might help. :smile:

A scan tool helps with diagnosis of this.....

If the scan tool reading data, is reflecting what is happening with the cluster, it's not the cluster, it's the wiring or the sensor....

If the scan tool was reading a constant speed and the speedometer was erratic, then it's the cluster or the wiring between the PCM and the cluster....

A scan tool helps with diagnosis of this.....

If the scan tool reading data, is reflecting what is happening with the cluster, it's not the cluster, it's the wiring or the sensor....

If the scan tool was reading a constant speed and the speedometer was erratic, then it's the cluster or the wiring between the PCM and the cluster....
Yes, forgot to mention we did put scanner on it and verified that the sensor was reading the erratic input after we swapped out cluster...did cluster first since it was a quick matter to do and if it turned out the fix..all the better.