Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Key On Engine Off (KOEO) On-Demand Self-Test
The KOEO on-demand self-test is a functional test of the PCM or the TCM, and is carried out on demand with the ignition key in the ON position and the engine OFF. This test carries out checks on certain input and output circuits. A fault must be present at the time of testing for the KOEO self-test to detect the fault. When a fault is detected, a DTC is output on the data link at the end of the test when requested by a diagnostic tool. The KOEO on-demand self-test can be executed with the gear selector in PARK only.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.