99 Blazer 4WD LT Instrument Cluster ?
 

My 99 Blazer has instrument cluster problems. Tach jumps randomly, lights(brake, ABS, low fuel, all of them) flash randomly, gas guage stays on 1/4 tank. About the only thing still working fairly correctly is the speedometer, which at times is about 10MPH off, verified by my GPS. everything is random. Any ideas? I got a ECM and cluster from junk yard but haven't tried replacing either yet. I found out that I have to have the ECM programmed before installing, so guess that was a waste. Also the odometer no longer works. Lights up once in a while, but isn't even close to actual mileage. One day it was all zeros and was going up as I drove. Best guess approximately 200,000 miles.

Thanks in advance for your input,

William

The PCM, BCM, TCCM, and EBCM all gather data and share the serial data through ClassII communications. The BCM ultimately controls the instrument cluster. You'll need a bi-directional scan tool capable of accessing and commanding functions of the BCM to troubleshoot the problem.

Would this tool connect to the diagnostic connector to communicate? I have taken it to Autozone and Advance and neither one can communicate with it

Yes, the scan tool connects to the data link connector under the dash. The el cheapo scan tools that the auto parts stores use can NOT access the BCM. It must be a bi-directional scan tool capable of accessing and commanding functions in the BCM. Ebay usually has some decent used ones starting around $2K. A GM dealer can diagnose the problem for around $100.