Rick's Free Auto Repair Advice

Chevrolet P0597

Diagnose and fix Chevrolet P0597 trouble code

Small modern engines are more efficient than older designs. They create less heat and hold less coolant. As a result, they provide less cabin heat, which can be a problem in cold climates. Since these engines don’t heat us as fast and a less efficient engine or produce as much heat, GM has installed heaters in the thermostats on these engines. The heater causes the thermostat to open more quickly than normal on cold days which allows hot engine coolant to circulate faster into the heater core and provide heat to the driver and passengers. Unfortunately, many GM cars with these engines suffer a Chevrolet P0597 trouble code. P0597 Engine Coolant Thermostat Heater Control Circuit

What causes Chevrolet P0597

Here’s how the electrically controlled thermostat works. Power is provided to the heater on the violet/blue wire from fuse 23 in the underhood fuse box. Backprobe this wire with the key in the RUN position to check for battery voltage.

To complete the circuit, the PCM provides a pulse width modulated (PWM) ground. Check for ground on the dark blue wire using a scope or averaging digital meter. The PCM regulates how much power the heater receives by altering the pulse time for the ground.

If you see battery voltage and ground, perform the following tests:

Disconnect the connector to the thermostat and check for resistance across the heater power and ground terminals. You should see around 3Ω. If the reading is higher, replace the thermostat. If it’s lower, the heater has an open and the thermostat should be replaced.

Next, check for continuity between the heater pin 1 and the thermostat housing. The reading should be open or an infinity symbol. If you see any other reading, you’ve got a heater short to ground.

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Posted on by Rick Muscoplat


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