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
- Difficult To Start/No Start (Engine Will Not Crank Or Cranks Slowly)
- Difficult To Start/No Start (Cranks Okay)
- Engine Stalls Often
- Engine Stalls Sometimes
- Rough Idle/Missing
- High Idle Speed (No Drop)
- Engine Backfires (Lean Fuel Mixture)
- Muffler Explosion (Rich Fuel Mixture)
- Engine Hesitates/Poor Acceleration
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, 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.
Wiring Harness Testing
If vibration is suspected as cause of an intermittent, lightly shake wiring harness vertically and horizontally while monitoring suspected circuit or component with a DVOM. Look for a voltage fluctuation during this test procedure. Inspect connector joint, fulcrum of the vibration and body through-portion. (Scheme 120)
Component & Sensor Testing
Lightly vibrate suspect component, relay or sensor, while monitoring suspected circuit or component with a DVOM. Look for a voltage fluctuation during this test procedure. (Scheme 120)
Electrical Connector Testing
Lightly shake connector vertically and horizontally, while monitoring suspected circuit or component with a DVOM. Look for a voltage fluctuation during this test procedure. Visually inspect connector and repair as required.
