Missing Tach

Howdy,

Does a GTP ECM rely on the white tach wire from the ICM or does it calculate it internally like a Regal did? I took the white wire straight off of the ICM to my Autometer tach (which doesn't show anything weirdly) and the scanner wasn't showing any rpm on the gauge either.

Just trying to figure it out.

Thanks,

I don't believe the IP uses that white wire from the ICM, but derives the tach signal from the PCM (much like the fuel level).

However, you should be seeing something from the white tach signal wire when hooked up to a regular tach.

On mine, I vaguely remember there were two white wires, and the "right" white wire was present on one side of the plug, but it wasn't on the other...

Got the Tach to come up in the scanner, now to figure out why Autometer doesn't read.