SYMPTOM DIAGNOSIS
Symptom checks cannot be used properly unless the problem occurs while the vehicle is being tested. To reduce diagnostic time, ensure steps in appropriate BASIC TESTING - GASOLINE and TESTS W/CODES articles are performed before diagnosing a symptom. Symptoms available for diagnosis are as follows
- No Start Or Hard Start
- Starts But Stalls
- Hard To Start - Cold Engine
- Erratic Idle Or Surging
- Backfiring
- Incorrect Idle Speed
- Hesitation - Acceleration
- Knocking
- Engine Misfire - All Conditions
- Insufficient Engine Power
- Poor Fuel Economy
- Excessive HC & CO
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplicating circuit or component failure to identify the problem. These procedures may lead to PCM setting a Diagnostic Trouble Code (DTC) which may help in diagnosis.
If problem vehicle does not produce DTC, 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.