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 DIAGNOSTIC PROCEDURES and SELF-DIAGNOSTICS articles were performed before diagnosing a symptom. Symptoms available for diagnosis include following
- Difficult To Start
- Surges
- Lack Of Power
- Spark Knock/Detonation
- Hesitation, Sag Or Stumble
- Cuts Out Or Misses
- Poor Fuel Mileage
- Rough Or Unstable Idle
- Excessive Exhaust Emissions Or Odors
- Backfire
- Dieseling (Run-On)
Note. If engine cranks, but will not start, see appropriate BASIC TESTING article for trouble shooting procedure.
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 fault has been located.
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.
See also:
• ADJUSTMENTS - EFI