For those of you having gm obd1 with code 42 and having a GM pre 1995 vehicle and getting the check engine light in your dash, please read carefully below. (For GM vehicles made before 1995 that has a distributor type ignition and has code 42-EST circuit failure and has the following symptoms:
Stalling at stop signs
No start but if you wait up to 2 hours, it will start again
TESTS for GM obd1 with code 42:
1.) Please confirm this gm code first by resetting the code and see if the code will show up again a second time. You reset obd1 codes by disconnecting the negative battery terminal for 1 minute and reconnect. If the code shows up again, it means this code is really a hard code that must be fixed. During no start, confirm the presence of ignition problem by checking the presence of spark using an especial tool ST125(cost under $5) and available in any local parts store.
2.)Make sure there is 12 volts supply going to your distributor harness wire when you turn the key on engine off (KOEO).
FIX for GM obd1 with code 42:
Remove the distributor assembly and replace the following:
Pick up coil
Once the above parts are replaced, reset the code and go for a quick road test to confirm. If your engine does not have a distributor, replace the crank sensor instead of the pick up coil. But check also for input voltage to the crank sensor harness wire. In some cases, the crank sensor magnet probe could be cracked and make sure to check them by removing the sensor for close visual inspection.
When checking the components for gm obd1 with code 42, you are better off using a wiring diagram or a vehicle service manual. This way you can avoid removing the wrong part. This is especially true when you try to identify the electrical components using the colors of the wires which are shown in the wiring diagram. If you need assistance, contact ATS.