SYMPTOM DIAGNOSIS
Symptom checks cannot be used unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC TESTING and TESTS W/CODES articles were performed before diagnosing a symptom. Following symptoms are available for diagnosis.
- Difficult To Start/No Start (Cranks Okay)
- Rough Or Unstable Idle
- Engine Hesitates Or Poor Acceleration
- Engine Surges
- Detonation Or Knocking
- Poor Fuel Mileage
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 switch is in ON position or engine is running. Ensure ignition switch is in OFF position or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of fault.