Code 42 - Est Circuit Open Or Grounded: Notes

Code 42 indicates ECM has seen an open or short to ground in HEI EST or by-pass circuit.

1. This test confirms Code 42 and determines if fault is a hard failure or intermittent condition.
2. This test checks for a normal EST ground path through ignition module. If EST circuit is shorted to ground, reading will be less than 500 ohms.
3. As test light voltage touches by-pass circuit, module should switch. This will cause ohmmeter to switch from hundreds of ohms to thousands of ohms. This test assures module "switched".
4. If module did not switch, this tests for a short in EST circuit, an open in by-pass circuit and a faulty ignition module connection or module.
5. This step confirms Code 42 is a faulty ECM and not an intermittent problem in EST or by-pass circuits.