Code 42 - Electronic Spark Timing (Est)

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

1. This test confirms Code 42, and that fault is present.
2. This test checks for a normal EST ground path through the ignition module. If circuit 423 is shorted to ground, reading will be less than 500 ohms.
3. As test lamp voltage touches circuit 423, the module should switch. This will cause the ohmmeter to "overange" if meter is in the 1000-2000 ohm position. A higher ohm range will indicate over 5000 ohms. This test assures that the module "switched".
4. If module did not switch, this step will test for a short in circuit 423, an open in circuit 424, and a faulty ignition module connection or module.
5. This step confirms that Code 42 is a faulty ECM and not an intermittent problem in circuits 423 and 424.

Fig 1: Code 42 Schematic (1.8L), Electronic Spark Timing (EST)

Fig 2: Code 42 Schematic (2.5L), Electronic Spark Timing (EST)

Fig 3: Code 42, Electronic Spark Timing (EST)

Fig 4: Code 42, Electronic Spark Timing (EST)