Code 42, Est Circuit Open Or Grounded: Notes

WARNING: This page is about a different car, the 1990 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.

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

NOTE: Test numbers refer to test numbers on diagnostic chart.

Test Number 1) This test confirms Code 42 and determines if fault is a hard failure or intermittent condition.

Test Number 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.

Test Number 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".

Test Number 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.

Test Number 5) This step confirms that Code 42 is a faulty ECM and not an intermittent problem in circuits No. 423 and 424.