SYMPTOM DIAGNOSIS
Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure BASIC DIAGNOSTIC PROCEDURES in the BASIC TESTING article and SELF-DIAGNOSTIC TESTS in the TESTS W/CODES article were performed before diagnosing a symptom. Following symptoms are available for diagnosis.
- Afterfire (Afterburn)
- Backfire
- Engine Stalls
- Engine Run-On (Dieseling)
- Excessive Fuel Consumption
- Hard Start/Will Not Start (Cold)
- Hard Start/No Restart (Hot)
- Hesitation, Flat Spot Or Surge
- High Idle (No Return To Idle)
- Lack Of Power/Poor Acceleration (Stumble)
- Rough Idle
- Spark Knock (Pinging)
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplicating circuit or component failure to identify problem. These procedures may lead to computer setting a fault code (on some systems) which may help in diagnosis.
If problem vehicle does not produce fault codes, monitor voltage or resistance values using a DVOM while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates a fault has been located.
Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition is on or engine is running. Ensure ignition is off or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of fault.