DTC 42

Code 42 - Electronic Spark Timing (EST):

Wiring Diagram for Electronic Spark Timing (EST):

CODE 42 - ELECTRONIC SPARK TIMING (EST)

Circuit Description:


Code 42 means the ECM has seen an open or short to ground in the EST or bypass circuits. A "Scan" tool does not have any ability to help diagnose a Code 42 problem.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. Confirms Code 42 and that the fault causing the code is present.

2. Checks for a normal EST ground path through the ignition module. An EST CKT 423 shorted to ground will also read less than 500 ohms; however, this will be checked later.

3. As the test light voltage touches CKT 424, the module should switch causing the ohmmeter to "overrange" if the meter is in the 1000-2000 ohms position.


Selecting the 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 CKT 423 shorted to ground.

^ Bypass CKT 424 open.


^ Faulty ignition module connection or module.


5. Confirms that Code 42 is a faulty ECM and not an intermittent in CKTS 423 or 424.