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 BASIC TESTING article and SELF-DIAGNOSTICS in TESTS W/CODES article were performed before diagnosing a symptom. The following symptoms are available for diagnosis.
- Backfire
- Engine Stalls
- Engine Stalls Under Acceleration/Deceleration
- Engine Stalls Under Heavy Electrical Load
- Engine Run-On (Dieseling)
- Excessive Fuel Consumption
- Hard Start/Will Not Start
- Hesitation, Flat Spot Or Surge
- High Idle (No Return To Idle)
- Hunting
- Lack Of Power
- Rough Idle
- Spark Knock (Pinging)
- Surge
- Unstable Idle
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 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.