Code 42 - Electronic Spark Timing

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 still present.
2. Checks for a normal EST ground path through ignition module. An EST circuit 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 circuit 423 shorted to ground, bypass circuit 424 open or a faulty ignition module connection or module.
5. Confirms that Code 42 is a faulty ECM and not an intermittent in circuits 423 or 424.

Fig 1: Code 42 Flow Chart, Electronic Spark Timing

Fig 2: Code 42 Flow Chart, Electronic Spark Timing

Fig 3: Code 42 Schematic, Electronic Spark Timing