Inventory Upgrade-Thermostat Dislodged Center Pin-Diagnose/Repair

One or both of the engine coolant thermostats in a small number of these vehicles may have a dislodged center pin, which can cause these vehicles to exhibit symptoms such as poor heater performance and/or Malfunction Indicator Light (MIL) illumination (DTC P0218).

Dealers are to perform an engine heating test to determine if the thermostats are functioning correctly and, if necessary, reposition the thermostat center pin.

Diagnosis Procedure

1. Connect the Tech II diagnostic tool and go to "Engine Data List 1".
2. Verify that there is no Winter Cover on the front of the truck.
3. Monitor the Engine Coolant Temperature (ECT) Sensor on the Tech II using the Fahrenheit scale.
4. Start the engine and keep the transmission in "park" (automatic) or "neutral" (manual) with parking brake set for the entire test.
5. Turn off the heater.
6. Let the engine idle for 1 minute.
7. Depress the accelerator pedal to the floor in order to maintain a 2,800-3,200 engine RPM and hold until the ECT sensor reaches 185°F (85°C) or for a maximum of 5 minutes.
8. This time frame is based on an ambient temperature range of 32 to 80°F (0 to 27°C) . (If the ECT does not reach 185°F (85°C) within 5 minutes, the thermostat must be accessed for repair.)
9. Return the engine to idle.
10. Turn the heater temperature to "hot" and the heater blower to "high" until the ECT drops back to 180°F (82°C) and then shut the heat off.
11. Monitor the ECT sensor temperature.
12. If the temperature drops below 170°F (77°C), the thermostat needs to be repaired.
13. If the temperature regulates above 170°F (77°C), the thermostat is operating properly and no repair is necessary.

Thermostat Pin Dislodged Repair Procedure

1. Remove the thermostat housing cover according to the Thermostat Replacement procedure in SI.



2. Once the thermostats are exposed, check to see if the thermostat center pin is dislodged.





3. To repair the thermostat(s), use your thumbs to push the thermostat down against the spring in order to reinstall the pin correctly in the alignment hole of the cross brace.
4. Reinstall the thermostat assembly housing cover. Refer to Thermostat Replacement in SI.

Parts are currently available from GMSPO, but should only be required if the service repair cannot be made.

Important: Most or all of these vehicles will not require a new thermostat.

US Dealers

This correction should be performed on all vehicles currently in your inventory that are included in the Administrative Message VIN list prior to sale or delivery.

Canadian Dealers

This correction should be performed on all vehicles currently in your inventory that are included in the VIN list sent with this message, prior to sale or delivery.