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.
Self-Diagnostic System: Description: Notes
PCM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, PCM will store a Diagnostic Trouble Code (DTC) and, in most cases, illuminate the Service Engine Soon (SES) lamp, also called the Malfunction Indicator Light (MIL) located on instrument cluster. Malfunctions are recorded as hard failures or intermittent failures.
There are 4 types of DTC categories:
- Type "A"
Emissions related. Illuminates MIL the first time DTC sets. - Type "B"
Emissions related. Illuminates MIL if fault is active for 2 consecutive driving cycles. - Type "C"
Non-emissions related. Does not illuminate MIL, but will illuminate SERVICE light. - Type "D"
Non-emissions related. Does not illuminate MIL or SERVICE light.
NO RELATED
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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.