2002 tachometer quit working

[Toobroke]

All, found this forum trying to troubleshoot an inoperative tach on my wife's 2002 Bravada (4.2 inline 6) AWD. I was actually driving it when the tachometer went erratic, then quit. I pulled over to the side of the road, lifted the hood, checked all the wiring connectors (didn't find anything loose). Hopped back into the drivers seat and the tach was working again. Lasted about a minute. Went erratic again and then stopped completely and hasn't worked since. No codes from my code reader. Not knowing about this forum I went to trailvoy and found a lot of info on the stepper motors, so I ordered 6 from a guy who most on that site recommended and changed them this afternoon. Tachometer is still not working. The Haynes manual I have does not show the tach at all in the wiring diagrams so I dug around some more on the internet and found out the white wire from the PCM is the tach wire. I ohms checked it from the PCM connector to the dash connector and it it ohm's checks good. I tried to see if there was an AC or DC voltage signal at the dash connector for the white wire and got nada. Also, the remote start starts the vehicle but it immediately shuts off. Is it possible that my PCM is bad? We had it changed about 3 years ago for an AWD problem and I really don't want to spend $1500 to fix a tach problem. Any other ideas? Thanks

[Chris Stewart]

Welcome to the site Toobroke,
Is everything else working ok?

[Toobroke]

Everything else is fine

[Chris Stewart]

I can't find any related info.
You might try a "re-boot",
Disconnect the battery, turn the light switch On for a few seconds then turn it Off.
Reconnect the battery and test ride.

[Toobroke]

Rebooted--no change

[Chris Stewart]

Any fuses blown?

[Toobroke]

Nope, no fuses blown

[ericn1300]

Don't look at me Chris, I don't own a vehicle made in this century yet.

[Chris Stewart]

Eric, so far all I've found the tach needle is driven by a "stepper" motor and toobroke replaced that with no improvement so we're basically looking at when drives the stepper motor...the pcm.
Hoping there's a module that's between the pcm & stepper motor, just haven't found any info to support that.

[Toobroke]

OK, I found it. It was the car starter wiring. The wire the car starter uses to sense the engine running was wore thru at the firewall. It was hooked up to the same white wire that sends a signal to the tach from the engine module. Why it didn't read shorted to ground still perplexes me. Anyways, a little black electrical tape and it's good-to-go. Thanks all for the suggestions

[Chris Stewart]

Good work Toobroke!!!
That was some impressive investigating!
Thank you for the update, it'll be useful to others I'm sure.

[rustymike12]

Good Job Toobroke, glad you found your problem. I have an '02 and it's good to know other people are out there shooting their own trouble and lettin' the rest of us know what they found.