Just bought a 98 TA auto and the tach doesn't work. I got another set of dials from another TA but they were from a different year and not suitable but I had the tach "motor" from them installed in the back of my dials and still it did not work. When you turn the car on the needle jumps from rest up to zero so there is power going to it OK. Any ideas? Is there a signal generator for the tach and where is it? Any help appreciated. BTW, does anyone know what the spare set of dials I got are for? The part # is 16232952JZA

 

The tach is driven by the PCM in these cars. You might want to check for a brocken tach wire that goes from the PCM to the tach.

 

Check the fuses as well, my tach stopped working, turned out I blew a fuse.

 

Anyone else got any ideas??

 

Anyone know how to access the tach wire between ECM and tach? The wiring loom runs right behind the engine along the bulkhead and looks almost impossible to remove for inspection. Hope you don't have to take out the engine to get at it! LOL

 

I think it's a white wire that runs from the PCM. There should be a white wire on the cluster harness as well.

 

OK Thanks..got my mechanic to check the white wire and it's fine. He reckons he's checked everything but has yet to check if the tach sensor in the engine bay has 3 wires coming off it instead of 2. If it has 3 wires he thinks maybe one side of the sensor is burnt out. Is he on the right track and if he is, any idea of replacement cost or a cure? ...Help!!

 

The problem seems to lie between the ECM and the sensor which monitors engine speed as everything between the ECM and the instrument gages is OK. Is it possible that the fault is within the ECM or maybe the sensor. Is the sensor which monitors engine speed the Crankshaft Position Sensor? If so, I am led to believe that if the CPS isn't working then the engine won't fire. Someone must know!! I need to get my tach working.

 

This system is quite complicated the ECM interprets the engine speed using the Crank position sensor and Camshaft position sensor then sends it out of pin 10 White wire (C2 ECM Red connector) through the fire wall behind the ECM to C105 and then to the ECBM for brake controlling. From there (somehow) it is combined into the Serial data code of the OBD2 maybe in the (ECBM) system and then seems to be re - interpreted back out by a Serial data connection to a module inside of the instrument cluster that feeds most of the major gauges temp speedo etc... Not sure why GM thought this needed to be so complicated, but it could any of those causing the issue. I guess they just thought it was cool to add all the gauge signals into Serial data. I am sure you don't even have the car anymore, but this may help someone else.