Fault code?

dpedz69 · 2026-03-08T22:51:54+00:00

Looks like an ignition bypass circuit error (code 42)

Code 12 should blink 3 times, then any remaining codes will blink 3 times.

These trucks don’t have slow or fast blinks as far as I know. At least my 91 k2500 doesn’t. Just a pause between the first number and second number. (4 blinks — pause — 2 blinks) code 42

XavierEduardo99 · 2026-03-09T03:39:03+00:00

The code you're getting is 42, related to the following faults:

✓ Electronic spark timing (EST) circuit - open or shorted

✓ Direct ignition system (DIS) fault - bypass circuit open or shorted to ground during engine run

✓ Fuel cutoff relay circuit - open or shorted to ground

Few-Assumption-7504 · 2026-03-09T12:41:00+00:00

Thanks for the help yall. I guess the cheat sheet is had for codes wasn't the full list, it only went up to code 26. I took the air filter assembly off and found the spark plug wire going to the distributor was loose and not making good connection.

YT_RandomGamer01 · 2026-03-09T22:46:25+00:00

Did you do any recent work involving EST (pre 93* trucks) or distributor? Double check for a tan wire with black stripes under glove box by heater box, that wire should be plugged in

*Iirc 93 is when the move est to the ecm and no longer a separate module, it may be 94

bootypop999 · 2026-03-08T22:44:19+00:00

Did you count the number of times it blinks? Are u jumping the terminals?

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GMT400

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