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 appropriate BASIC TESTING and appropriate TESTS W/CODES articles were performed before diagnosing a symptom. Symptoms available for diagnosis are as follows
- Does Not Start
- Difficult To Start
- Poor Idling
- Poor Driveability
- Engine Stalls
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.
Wiring Harness Testing
Using DVOM, monitor suspected circuit or component. Lightly shake wiring harness while noting fluctuation in DVOM reading. Inspect component connector harness for stretched areas. Inspect wiring harness at area where it goes through the body.
Component, Relay & Sensor Testing
Using DVOM, monitor suspected circuit or component. Lightly vibrate suspected component, relay or sensor while noting fluctuation in DVOM reading.
Electrical Connector Testing
Using DVOM, monitor suspected circuit or component. Lightly shake electrical connector while noting fluctuation in DVOM reading. Visually inspect electrical connector for damage.
Component Testing
Heat the suspected component with a hair dryer while checking for a malfunction to exist. DO NOT apply heat directly to the components in the Engine Control Module (ECM). DO NOT heat any component to more than 140°F (60°C).