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.
Monitored Circuits
The PCM contains electronic circuit monitors that monitor fuel, vehicle emissions, engine and ignition system performance. Monitors do not indicate a specific component failure, but do indicate an implied failure within a specified system, and that the problem must be diagnosed. If any monitor detects a problem affecting vehicle emissions, a Diagnostic Trouble Code (DTC) will be stored in PCM and MIL will be illuminated. The following monitors are used:
- EGR Monitor
- Engine Misfire Monitor
- Fuel System Monitor
- Oxygen Sensor Monitor
- Oxygen Sensor Heater Monitor
- Catalyst Monitor
- EVAP System Leak Detection Monitor
When the MIL is illuminated, a DTC is stored. The DTC can self-erase only when MIL is out. When MIL is out, PCM must pass a diagnostic test for the most recent DTC for 40 warm-up cycles (80 warm-up cycles for fuel system monitor and misfire monitor).
A warm-up cycle is defined as the engine is started, an increase of 40°F (4°C) in engine coolant temperature exists after engine is started, and engine coolant temperature reaches at least 160°F (71°C). Engine is shut off.
DTCs may be retrieved for system diagnosis. See RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM.
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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.
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