Conditions For Setting DTC
WARNING: This page is about a different car, the 2003 GMC Sierra 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 of more than 27°F (15°C) between the ECT and the IAT, the vehicle must be driven for 7 minutes over 15 MPH. If the IAT decreases more than 5° F (3° C) then a block heater is indicated and the test is aborted. If the IAT temperature does not decrease, a block heater was not detected and this DTC will set.