Code 42, Est Circuit Open Or Grounded: Notes

Code 42 indicates the 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 the 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, the module should switch. This will cause the ohmmeter to switch from hundreds of ohms to thousands of ohms. This test assures that the module "switched".
4. If module did not switch, this step will test for a short in circuit No. 423, an open in circuit No. 424, and a faulty ignition module connection or module.
5. This step confirms that Code 42 is a faulty ECM and not an intermittent problem in circuits No. 423 and 424.