Conditions For Setting DTC
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Suburban, and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
If the PCM detects a temperature difference between the ECT sensor and the IAT sensor of more than 27°F (15°C), then the vehicle must be driven for more than 400 seconds over 15 mph. If the IAT sensor temperature decreases more than 5°F (3°C), a block heater is detected and the test is aborted. If the IAT sensor temperature does not decrease, a block heater was not detected and DTC P0116 sets.