Code 42: Electronic Spark Timing (Est) With HEI Ignition: Notes

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

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 tests for a normal EST ground path through the ignition module. If circuit No. 423 is shorted to ground, reading will be less than 500 ohms.

Test Number 3) As test light voltage touches circuit No. 424, the module should switch. This causes ohmmeter to "over-range" with meter in 100-200 ohm range. A higher ohm range will indicate over 5000 ohms. This test assures the module switched.

Test Number 4) If module did not switch, this step tests 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 Code 42 is a faulty ECM and not an intermittent problem in circuits No. 423 and 424.