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 BASIC TESTING article in this section were performed before diagnosing a symptom. Symptoms available for diagnosis include the following
- Hard Starting (Cranks Okay)
- Engine Surges
- Lack Of Power, Sluggish Or Spongy
- Detonation/Spark Knock
- Hesitation, Sag Or Stumble
- Cuts Out, Misses
- Rough, Unstable Or Incorrect Idle
- Poor Fuel Economy
- Excessive Exhaust Emissions
- Engine Diesels
- Engine Backfires
Note. Systems and components listed under each symptom may not be applicable on all models.
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplicating circuit or component failure to identify the problem. These procedures may lead to the 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.