SYMPTOM DIAGNOSIS
| CAUTION | When battery is disconnected, vehicle computer may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION before disconnecting the battery. |
Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC DIAGNOSTIC PROCEDURES article and appropriate SELF-DIAGNOSTICS article were performed before diagnosing a symptom. Following symptoms are available for diagnosis
- ABNORMAL ENGINE NOISE
- A/C DOES NOT TURN OFF DURING WIDE OPEN THROTTLE (WOT)
- A/C IS ALWAYS ON OR COMPRESSOR RUNS CONTINUOUSLY
- CONSTANT VOLTAGE
- CRANKS NORMALLY BUT WILL NOT START
- EMISSIONS FAILURE
- ENGINE RUNS ROUGH, MISSES, HESITATES, STUMBLES, SURGES OR STALLS DURING ACCELERATION OR CRUISE, OR ENGINE BUCKS OR JERKS DURING ACCELERATION, CRUISE OR DECELERATION
- ENGINE STALLS AT IDLE OR JUST AFTER STARTING
- ENGINE VIBRATION
- EXCESSIVE OIL CONSUMPTION
- EXHAUST SMOKE
- EXHAUST SULPHUR (ROTTEN EGG) SMELL
- FAST IDLE OR RUN-ON
- FUEL ODOR IN ENGINE COMPARTMENT
- HARD TO START (LONG CRANKING, ERRATIC CRANKING OR ERRATIC STARTING)
- KNOCKING OR PINGING DURING ACCELERATION OR CRUISE
- LACK OR LOSS OF POWER DURING ACCELERATION OR CRUISE
- LOW IDLE OR ENGINE STALLS DURING DECELERATION
- POOR FUEL MILEAGE
- ROUGH OR UNSTABLE IDLE
- SLOW RETURN TO IDLE
- WILL NOT CRANK
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplicating circuit or component failure to identify problem. On some systems, 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.