agillings

My 1985 C4 350, Auto, all stock runs Perfect! When I start the Eng the Service Eng soon light will stay on until the eng warms up and stays out and no error codes. What do you thing will cause this?

barrypaul2005

You should be getting that blinking 3x one-two code when you ground the diagnostic terminal with the ignition on and engine stopped. That will at least tell you if your ECM is operating properly.

In any case, good idea to reset the ECM by disconnection from the battery for ten seconds to reset it.

Otherwise, I never heard of the SES light staying on for a long period with no stored codes - I'd say that's pointing to the ECM itself. Manual says if the problem is intermittent (with a good ECM), the SES light will come on for 10 seconds but will store the trouble code of that intermittent problem source.

Kevova

Check ecm grounds clean and tight. Make sure (EST) 4 wire harness from distributor is at least 1 inch away from plug wires. Good luck

84CFIAuto

My 84 has a similar quirk.

The light comes on randomly during normal driving, its been checked by myself, a buddy and a local Vette enthusiast, yet no code.

The car runs great and has no issues, so Im not worried about it.
Its a 31 year old ride, its gonna have a few bugs.