Originally posted by robot
VCM is the vehicle control module....the computer to all of us. The computer is pretty rugged and fails less than it gets credit for. Most of the connections are either reading a voltage (like from a temperature sensor) or making a circuit. The computer outputs are sinking....that is, they complete a ground circuit rather than furnish a voltage....pretty immune stuff.

ICM is ignition control module, on a Vortec, it is a blob next to the coil and it has the heatsink on it.....kinda equvalent to the HEI module under the cap on the older distributors.

One more thing, the way the truck ran when it was limping home should give more info......if it was a detectable fault, the trouble code was stored in the memory and the MIL (check engine)light was illuminated. If the thing limped home with the MIL on, it was in a "limp" mode.

Also, the stuff that got us older guys in the past is still valid......a crack in the rotor or cap that grounds the spark will still apply. Even though the OBD systems are really smart, they only point you in a direction.

mike in tucson
robot, you need to go back and read the rest of this thread. and by the way that motor has a dist. and module just like the old HEI did.