SYMPTOM DIAGNOSIS
When a diagnostic code cannot be confirmed or problem cannot be confirmed in BASIC DIAGNOSTIC PROCEDURES, find basic symptom. For example, vehicle will not start. Appropriate heading matching vehicle symptom is DOES NOT START. Listed under DOES NOT START are more specific conditions. Find specific condition which best describes vehicle malfunction. Perform checks in order given. DO NOT skip steps.
Note. Even if a diagnostic code is not set, this article may refer you to a test procedure for a specific diagnostic code in TESTS W/CODES article.
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplicating circuit or component failure to identify the 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 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.