Code 42, Electronic Spark Timing (All Engines)

Code 42 means the ECM has seen an open or short to ground in the EST or bypass circuit.

1. Confirms Code 42 and that the fault causing the code is present.
2. Checks for a normal EST ground path through ignition module. An EST CKT 423 shorted to ground will read less than 500 ohms.
3. As the test light voltage touches terminal "D5", the module should switch changing the ohmmeter reading to over 5000 ohms. The important thing is that the module "switched".
4. Check for the EST CKT 423 shorted to ground, bypass CKT 424 open or a faulty ignition module connection or module.
5. Confirms that Code 42 is a faulty ECM and not an intermittent in CKTS 423 or 424.

Fig 1: Code 42, Electronic Spark Timing

Fig 2: Code 42 Schematic