DTC 42

CIRCUIT DESCRIPTION
Code 42 means the Engine Control Module (ECM) has seen an open or short to ground in the EST or by-pass circuits.

CHART TEST DESCRIPTION
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.