Using Block Heater Sets Engine Light in 2005 Duramax Diesel

When I plug in the block heater of my 2005 Duramax, the engine light comes on shortly after I start the engine. The problem does not occur when the truck is not plugged in. What is going on?

This is a problem caused by the ECM getting confused when it does a rationality check between the engine coolant temperature sensor and the fuel temperature sensor.

Usually one or both of two DTCs set:

P0116 – Engine Coolant Temperature (ECT) Sensor Performance
P0181 – Fuel Temperature Sensor Performance

What occurs to set the DTC is that the engine temperature reads significantly different than the fuel temperature sensor, which can certainly happen when the engine block heater is functioning in a cold climate. This may seem like a big oversight on the part of GM engineering, but they did take into account the operation of the engine block heater when programming the diagnostic. How so?

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Joel Paynton is an award-winning GM technician who specializes in Duramax fuel systems. He also does custom programming for any GM powertrain. Visit him on the web at www.payntonperformance.com.