Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1992JIMMY BASE, 2D UTILITY, 4.3 W, RWD, AUTOMATICREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODES - 2.5L & 2.8LTROUBLE CODESCODE 42, ELECTRONIC SPARK TIMINGNOTES
1992 GMC Jimmy Base, 2D Utility, 4.3 W, RWD, Automatic
Code 42, Electronic Spark Timing: Notes
1992 GMC Jimmy Base, 2D Utility, 4.3 W, RWD, AutomaticSECTION Notes
NOTE:
For applicable schematic, see previous page.
Code 42 indicates ECM has seen an open or short to ground in High Energy Ignition Electronic Spark Timing (HEI EST) system or by-pass circuits.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This test confirms Code 42 and determines if fault is a hard failure or intermittent condition.
- This tests for a normal EST ground path through ignition module. If circuit No. 423 is shorted to ground, reading will be less than 500 ohms.
- As test light voltage touches circuit No. 424, 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 module switched.
- 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.
- This step confirms Code 42 is a faulty ECM and not an intermittent problem in circuits No. 423 and 424.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.