- Turn the ignition OFF . If possible, allow the vehicle to sit with the ignition off for more than 8 hours in an environment where the temperature is consistent and above 20°F (-7°C).
- Test drive the vehicle. The vehicle must exceed 30 mph (48 km/h) during the test drive. Do not cycle the ignition off when the test drive is completed.
- With a scan tool, select View DTCs.
- Turn the ignition off. Allow the vehicle to sit with the ignition off in an environment where the temperature is consistent and above 20°F (-7°C) until the engine coolant temperature is equal to ambient temperature. Turn the ignition on. With a scan tool, compare the AAT, ECT, and IAT sensor values.
- If the ECT sensor value is not within 18°F (10°C) of the other two sensor values , perform the following:
- Refer to any Technical Service Bulletins (TSBs) that may apply.
- Review the scan tool Freeze Frame information. If possible, try to duplicate the conditions under which the DTC set.
- With the engine running at normal operating temperature, monitor the scan tool parameters related to the DTC while wiggling the wire harness. Look for parameter values to change and/or a DTC to set. Turn the ignition off.
Visually inspect the related wire harness. Disconnect all the related harness connectors. Look for any chafed, pierced, pinched, partially broken wires and broken, bent, pushed out, or corroded terminals.
Perform a voltage drop test on the related circuits between the suspected inoperative component and the ECM.
CAUTIONDo not probe the ECM harness connectors. Probing the ECM harness connectors will damage the ECM terminals resulting in poor terminal to pin connection. Install Miller Special Tool no. 8815 to perform diagnosis.
- Inspect and clean all ECM, engine, and chassis grounds that are related to the most current DTC.
- If numerous trouble codes were set, use a wire schematic and look for any common ground or supply circuits.
- For any Relay DTCs, actuate the Relay with the scan tool and wiggle the related wire harness to try to interrupt the actuation.
- For intermittent Evaporative Emission trouble codes perform a visual and physical inspection of the related parts including hoses and the Fuel Filler cap.
- Use the scan tool to perform a System Test if one applies to failing component. A co-pilot, data recorder, and/or lab scope should be used to help diagnose intermittent conditions.