LBZ, LB7, LLY, Service Engine Soon (SES) Light Illuminated, DTC P0116, P0181 Set with Engine Coolant Heater Usage in Ambient Temps Above -18 Degrees C (0 Degrees F) (Replace Engine Coolant Heater Cord

Some customers may comment on a Duramax™ Diesel vehicle with a Service Engine Soon (SES) light illuminated on the instrument cluster. Some vehicles may have been previously serviced for this same condition. Technicians may also find the following DTCs set with no concern found.

The Fuel Temperature Sensor, Engine Coolant Temperature (ECT), and Intake Air Temperature (IAT) sensors are compared to each other during a cold start to identify a concern with any one of the sensors. Engine coolant heater usage in ambient temperatures above -18°C (0° F) may trigger a false DTC P0116 or P0181.

The diesel supplement to the Owner’s Manual advises that the engine coolant heater may be used below -18°C (0°F) to assist with cold starts. However, a customer may wish to plug in the heater when the overnight temperatures are unknown. A thermostatically controlled engine coolant heater cord is available for the prevention of false DTCs. This cord incorporates a thermostatic switch that only conducts below -18°C (0°F).

Follow the steps below for the particular model year vehicle you are working on to ensure that the correct diagnostics are performed before replacing the engine coolant heater cord.

2001-2002 Vehicles

1. Verify that the updated calibration per Corporate Bulletin Number 02-06-04-058 has been installed.
2. Follow the published diagnostics in SI.
3. If no concern is found, determine if the customer is using the engine coolant heater above -18°C (0°F).
4. If the customer is using the engine coolant heater in ambient temperatures above -18°C (0°F), then replace the original coolant heater cord with the thermostatically controlled engine coolant heater cord, GM P/N 10369173.

2003-2006 Vehicles

1. Verify that the latest calibration has been installed.
2. Follow the published diagnostics in SI.
3. If no concern is found, determine if the customer is using the engine coolant heater above -18°C (0°F).
4. If the customer is using the engine coolant heater in ambient temperatures above -18°C (0°F), then replace the original coolant heater cord with the thermostatically controlled engine coolant heater cord, P/N 10369173.

For vehicles repaired under warranty, use: