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.
KOEO & KOER SELF-TEST Codes
All service codes are 2- or 3-digit numbers. PCM outputs codes one digit at a time. These codes indicate current faults in system and should be serviced in order of appearance. Use SERVICE CODE REFERENCE CHARTS to find correct CIRCUIT TEST.
Codes are shown as voltage pulses. If using MIL/CHECK ENGINE light, service codes are displayed as light pulses. If using Volt-Ohmmeter (VOM), service codes are displayed as needle sweeps. See Figure.
Pay careful attention to length of pauses in order to read codes correctly. A 1/2-second pause occurs between number of sweeps in a digit and a 2-second pause occurs between digits in a code.A 4-second pause occurs between each code. KOEO codes are separated from Continuous Memory Codes by a 6-second delay, a single 1/2-second sweep (Separator) and another 6-second delay. Record codes in order received.
Scan tester, if used, will count pulses and display them as a digital code. Star Series Tester will add a zero (0) to single-digit Separator Code (10) and Dynamic Response Code (10). Dynamic Response Code is displayed in KOER SELF-TEST. See Figure.
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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.