In 95 3 main computers were tied to gether on communication wires. Body, engine, and transmission. PCM, TCM, BCM, each has self diagnostics. The speedo gets it's signal from the vehicle speed sensor, the tach gets it's signal from the two sensors on the transmission(input and output) the voltmeter is driven by battery charging voltage by the body computer which drives the instrument cluster. If your having problems with any one of the three this could occur. What does the dealer say about the DRBIII they use to read all these systems. There may be a code for a bad TCM or BCM. They have bulletins regarding cluster ground problems also. Have you ever taken it in to the dealer so they can see if any fault codes are present? I think you may have a problem with the instrument cluster itself. A bad circuit board or ground or poweer wire in the connector behind the cluster. This was a common complaint. If I see any bulletins regarding this I'll let you know. Bulletin 08-07-94 Rev. B deals with the plug wires interfering with the input sensor wires causing bad signals, a bulletin 08-77-94 is for vehicle speed sensor problems causing speedometer flucuations the new part number was 4707386. The TCM had problems also bullrtin 08-15-99 is for reprogramming the TCM, which gives tachometer information that is used for shifting and by the BCM for the cluster.
Sunday, March 21st, 2010 AT 12:20 AM