DTC 42

Fig. 016 - Wiring Diagram for Code 42 Electronic Spark Timing. VIN 1:

CODE 42

ELECTRONIC SPARK TIMING (EST)

2.0L (VIN 1) "J" SERIES

FUEL INJECTION (TBI)

Circuit Description:
When the system is running on the Ignition Module, that is, no voltage onthe by-pass line, the Ignition Module grounds the EST signal. The ECM expects tosee no voltage on the EST line during this condition. If it sees a voltage, it sets Code 42 and will not go into the EST mode.
When the rpm for EST is reached (about 400 rpm) the EST should no longer be grounded in the ignition module so the EST voltage should be varying.
If the by-pass line is open or grounded, the ignition module will not switch to EST mode so the EST voltage will be low and Code 42 will be set.

Fig. 015 Chart - Code 42 Electronic Spark Timing:

Test Description:
Step numbers refer to step numbers on diagnostic chart.
1. Code 42 means the ECM has seen an open or short to ground in the EST or by-pass circuits. This test 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:
a. EST CKT 423 shorted to ground.
b. Bypass CKT 424 open.
c. Faulty ignition module connection or module.
5. Confirms that Code 42 is a faulty ECM and not an intermittent in CKT's 423 or 424.

Diagnostic Aids:
The "Scan" tool does not have any ability to help diagnose a Code 42 problem.
If Code 42 is intermittent, refer to symptoms.