Code 42 - Electronic Spark Timing

Code 42 means ECM has seen an open or short to ground in the Electronic Spark Timing (EST) or by-pass circuits.

1. Confirms Code 42 and that fault causing code is present.
2. Checks for normal EST ground path through ignition module. An EST circuit No. 423 shorted to ground will also read less than 500 ohms (will be checked later).
3. As test light voltage touches terminal 10 (circuit No. 424), module should switch, causing ohmmeter to "overrange" (meter is in the 1000-2000 ohms position). Selecting 10-20,000 ohms position will indicate above 5000 ohms. The important thing is that the module "switched".
4. The module did not switch and this step checks for:
   • EST circuit No. 423 shorted to ground.
   • By-pass circuit No. 424 open.
   • Faulty ignition module connection or module.
5. Confirms that Code 42 is a faulty ECM and not an intermittent in circuit Nos. 423 or 424.

Fig 1: Code 42, Electronic Spark Timing