SYMPTOM DIAGNOSIS
Symptom checks cannot be used unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC DIAGNOSTIC PROCEDURES and SELF-DIAGNOSTICS 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 Diagnostic Trouble Code (DTC) which may help in diagnosis.
If problem vehicle does not produce DTCs, 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. See PIN VOLTAGE CHARTS article. When monitoring voltage, ensure ignition switch is in ON position or engine is running. Ensure ignition switch is in OFF position when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of fault.