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
There are 4 codes displayed during this test. In order of display, these are an Engine ID code, a Dynamic Response code, Fast codes, and On Demand codes.
The first and third codes are not applicable in field tests. The Engine ID codes are displayed as 20, 30, or 40. The first digit is equal to half the number of cylinders in the engine. Fast codes are the same as those run during Key ON/Engine OFF Self-Test. Engine ID codes and Fast codes are used by automatic equipment during manufacturing processes.
The Dynamic Response code appears as the numeral 10. This code instructs the technician to open linkage to WOT position momentarily. This checks inside the TPS and MAPS for proper movement. If WOT does not occur within 15 seconds, the numeral (Code) 77 will be displayed. The On Demand codes are "hard faults" found in system outputs during test.
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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.