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.
System Diagnosis: Notes
The Electronic Control Unit (ECU) monitors several different engine control system circuits. If an abnormal input signal occurs, a fault code is stored in ECU memory and given a fault code number. Each circuit has its own fault number and message. A specific fault code results from a particular system failure. It is NOT necessarily the reason for that failure. The fault code does not condemn a specific component. The fault code calls out a probable malfunction area. If a critical fault code is set, the ECU will turn on CHECK ENGINE light. All fault codes except speed sensor are considered critical.
Fault codes can be confirmed by using a voltmeter, DRB-II, or appropriate scan tester. See ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER) or ENTERING ON-BOARD DIAGNOSTICS (USING DRB-II) . By using DRB-II, the self-diagnostic capabilities of this system can simplify testing and reduce diagnostic time.
System malfunctions encountered are identified as either hard faults or intermittent faults as determined by the ECU.
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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.