SYMPTOM DIAGNOSIS
Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC TESTING and TESTS W/CODES articles have been performed before diagnosing a symptom.
Symptoms available for diagnosis include
- Engine Will Not Start
- Difficult Cold Start
- Fast Idle Out Of Specification
- Rough Idle When Warm
- Idle RPM High When Warm
- Idle RPM Low When Warm
- Stalling During Warm-Up
- Stalling After Warm-Up
- Misfire Or Rough Operation
- Emission Test Failure
- Lack Of Power
Recommended system and component checks may not apply to all vehicles.
EMISSION TEST FAILURE
- Check Manifold Absolute Pressure (MAP) sensor for proper operation.
- Check Oxygen Sensor (O2S) for proper operation.
- Check catalytic converter for proper operation.
- Check EVAP system for proper operation.
- Check fuel system for proper operation.
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplicating circuit or component failure to identify problem. These procedures may lead to computer setting a Diagnostic Trouble Code (DTC) on some systems, which may help in diagnosis.
If problem vehicle does not produce DTCs, monitor voltage or resistance with DVOM while attempting to reproduce conditions causing intermittent problem. A status change on DVOM indicates a problem has been located.
Use a DVOM to pinpoint problems. When monitoring voltage, ensure ignition is on or engine is running. Ensure ignition is off or negative battery terminal is disconnected when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of problem.