LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Dtc 41 & 42

Old 06-14-2019, 10:55 PM
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Dtc 41 & 42

I just got a 94 camaro with a blown head gasket I replaced the head gasket and it ran great for 2 weeks then all the sudden one day it died on me was back firing and I got DTC 42 I changed ICM it ran good for another few days then had same code 42 come back. I got a new AC Delco ICM maybe I got a faulty one from the parts store, I also got a new ACdelco coil. Changed both of those and it still won't start. I get code 41 during cranking and code 42 comes back sometimes. Today I was checking grounds and cleaned all them and replaced the ground strap also cleaned the coil connectors and It fired up and idled very rough once I touched the ICM harness it shut off instantly. After that it will not start again. Any suggestions on what it could be?
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Old 06-15-2019, 12:35 AM
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Re: Dtc 41 & 42

Check the ICM connector, as shown in Shoebox’s guide. Sounds like a short in the connector or the wiring. Jiggle the cable and wiring during the test, to look for an intermittent condition.

4th Gen LT1 F-body Tech Articles

Just use the part about the ICM connector.
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Old 06-15-2019, 12:24 PM
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Re: Dtc 41 & 42

Replaced the coil connector and icm connector a wire was hanging by a thread the car fired right up. About 5 mins after ideling code 42 came back. Any other suggestions? I took all wire loom off and didnít see and burned or exposed wires. Maybe I try a better ground strap?
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Old 06-15-2019, 02:41 PM
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Re: Dtc 41 & 42

Did you check the voltage and ohms to ground on the ICM connector per Shoebox’s guide?
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Old 06-16-2019, 08:14 PM
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Re: Dtc 41 & 42

Yes they all checked out great. I unhooked the grounds and car still started with code 42, must be a wire somewhere grounding out I canít see.
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Old 06-17-2019, 11:33 AM
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Re: Dtc 41 & 42

If it started with DTC 42, it's had to be a stored code, not an active one, and the problem is intermittent. When DTC 42 is active, it shuts down the injectors. And DTC 42 can only set during cranking. Does not turn on the SES light. It sets when the PCM counts 84 crank revolutions (based on low res signal from the Opti) and does not see any activity from the ICM.

Does the engine ever fail to start when cranking for up to 15 seconds? That would be when the code is setting.

Download (free - courtesy of GaryDoug) the 94 factory service manual, and look at the DTC 42 diagnostics in Volume 2 of 2, page 6E3-A-86.

http://www.mediafire.com/?40mfgeoe4ctti
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Old 06-17-2019, 11:50 AM
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Re: Dtc 41 & 42

It runs with the code on, I clear it and it comes back instantly.I went through the diagnostics test that are in the shop Manual. Just runs rough and back fires out of exhaust
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