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 Running (KOER) Self-Test
The KOER self-test is a functional test of the PCM carried out with the engine running. The engine must be at operating temperature for the KOER self-test to operate. A check is made on the fuel rail pressure (FRP) sensor, turbocharger, and exhaust gas recirculation (EGR) systems. During this test, the engine RPM may vary. The brake pedal position (BPP) test is a part of the KOER self-test and must be carried out during this operation. A concern must be present at the time of testing for the KOER self-test to detect a concern. If a concern is detected, a DTC is output on the data link at the end of the test when requested by the scan tool.
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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.