How to Self Test the Check Engine Light for a C1500 Chevy

by Richard Ristow
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Car dashboard image by Andrejs Pidjass from

Not all cars feature self testing. That style of diagnostic procedure stopped in 1996, when the Environmental Protection Agency (EPA) standardized On-Board Diagnostics. Checking an engine made after 1996 requires a handheld scanner. If your Chevrolet C1500 has the ability to self test, then it was manufactured before General Motors began to phase in OBD-II coding. Although the diagnostic system is outdated, you can still self test the Chevrolet C1500.

Step 1

Print out Chevrolet's OBD-I check engine light flash codes. You can find them on the Internet; the C1500's manual does not have them. If you own a Haynes Repair Manual for your model year, you can find descriptions for Chevy's flash codes in the engine-related chapters. Place the manual or your print outs in the C1500's navigator seat.

Step 2

Craft a paper clip into a skinny "U" shape and place both ends into the "A" and "B" ports on the C1500's Assembly Line Data Link (ALDL). The ALDL is directly below the steering wheel, and the "A" and "B" ports are the last two in the upper row, on the far right.

Step 3

Place the C1500 into self testing mode. To do this, insert the C1500's key into the ignition and switch to the "On" position. Leave the C1500's engine off and uncranked.

Step 4

Count how many times the C1500's check engine light flashes and observe how long the flashes last. Each flash code is different. For example, GM flash code 19 consists of one long flash followed by nine pulse-like flashes. GM flash code 41 is four long flashes with one pulse-like flash. Write these down.

Step 5

Consult the resources you left in the C1500's navigator seat. The flash code definitions provide brief explanations of engine problems. Reread the code definitions and descriptions. Fix the problems if you are able. If not, hire a mechanic to fix the problem.

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