DTC 42

Code 42:

Ignition Wiring Diagram:

CODE 42

ELECTRONIC SPARK TIMING (EST) CIRCUIT


Circuit Description:

Code 42 indicates that the ECM has seen an open or ground at ECM terminal 11 or 12.
A grounded EST may sometimes not set a code unless cranked 10 seconds or longer with circuit grounded.


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

1. This checks operation of EST. Grounding the "test" terminal causes timing to go to a fixed value, which is normally different from that obtained with EST operating. Therefore, the timing should change. Usually, the change can be heard in engine rpm. If so, the timing change does not have to be checked. If timing varies with increase in engine rpm (module advance), a problem is indicated.

2. This step eliminates the ECM and ECM connections from the module input. By jumpering terminals "A" and "B", the distributor reference signal is fed directly into the EST line of the module, By putting voltage through the test light on terminal "C" of the harness, the module is switched to the EST mode and the vehicle should run. If the engine stops there is no EST signal reaching the module due to open or poor connections or the module is faulty.


3. By removing the jumper you are opening the EST signal and the engine should stop.

4. Since the engine ran when the module was jumpered, it says the problem is not in the distributor (if the correct HEI module is installed). The wrong HEI module can set a Code 42.

NOTE: Other possible causes for intermittent Code 42 are:

Loose grounds or electrical connections.

Extended cranking time (over 10 seconds with fully charged battery).

Abrupt re-cycling of ignition switch from "ON" to "OFF" and back "ON" again (within 5 seconds).

EST harness routed close to plug wires or other high load electrical harness.