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 in this section were performed before attempting to diagnose a symptom. Symptoms available for diagnosis include these symptoms.
- 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.
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.
TEST PROCEDURES
Intermittent Simulation
To reproduce conditions creating an intermittent fault, use following methods
- Lightly vibrate component.
- Heat component.
- Wiggle or bend wiring harness.
- Spray component with water.
- Remove/apply vacuum source. Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.