DTC 42

Code 42 means the ECM has seen an open or short to ground in the EST or bypass circuits.

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 13 shorted to ground will also read less than 500 ohms; however, this will be checked later.
3. As the test high voltage touches CKT 14 the module should switch causing the ohmmeter to "overrange" if the meter is in the 1,000-2,000 ohms position. Selecting the 10-20,000 ohms position will indicate above 5000 ohms. The important thing is that the module "switched".
4. If the module did not switch, check for:
^ EST CKT 13 shorted to ground.
^ Bypass CKT 14 open.
^ Faulty ignition module connection or module.

5. Confirms that Code 42 is caused by a faulty ECM and not an intermittent in CKT 13 or 14.