Diagnostic Instructions

DTC Descriptor

DTC P0597: Engine Coolant Thermostat Heater Control Circuit

DTC P0598: Engine Coolant Thermostat Heater Control Circuit Low Voltage

DTC P0599: Engine Coolant Thermostat Heater Control Circuit High Voltage

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Ignition Voltage Circuit	P0597, P0598*	P0597, P0598	--	--
Thermostat Control Circuit	P0597, P0598	P0597	P0599	--
*Opens the fuse that supplies voltage to the engine coolant thermostat

Circuit/System Description

The engine control module (ECM) controls the pulse width modulated (PWM) thermostat. The thermostat controls coolant flow and regulates the engine operating temperature. Ignition voltage is supplied directly to the thermostat. The ECM controls the thermostat by grounding the control circuit with a solid state device called a driver. The driver is equipped with a feedback circuit that is pulled-up to a voltage. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage.

Conditions for Running the DTCs

Conditions for Setting the DTC

The ECM detects that the commanded state of the driver and the actual state of the control circuit do not match for greater than 15 seconds.

Action Taken When the DTC Sets

DTCs P0597, P0598, and P0599 are Type B DTCs.

Conditions for Clearing the DTC

DTCs P0597, P0598, and P0599 are Type B DTCs.

Diagnostic Aids

The thermostat has a mechanical fail-safe in case of an electrical condition with the thermostat heater. The mechanical thermostat will open at approximately 104°C (220°F). The mechanical thermostat will cycle from approximately 104°C (220°F) to approximately 98°C (208°F).

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. DTC P0689 and P1682 should not be set.

⇒	If a DTC is set, refer to DTC P0685, P0689, or P0690.

2. Ignition ON, observe the following scan tool control circuit status parameters.

•	Eng Clnt Therm Htr Ckt Short Gnd Test Status

•	Eng Clnt Therm Htr Ckt Open Test Status

•	Eng Clnt Therm Htr Ckt Short Volts Test Status

Each parameter should display OK or Not Run.

3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the engine coolant thermostat heater.
2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 2 and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test all the components connected to the ignition circuit and replace as necessary.

3. Command the engine coolant thermostat heater to 10 percent with a scan tool. Test for 2.5-3.5 V between the control circuit terminal 1 and ground.

⇒	If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.

⇒	If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Command the engine coolant thermostat heater to 100 percent with a scan tool. The DMM should transition from 2.5-3.5 V when commanded to 10 percent to less than 0.1 V when commanded to 100 percent.

⇒	If the circuit voltage does not correspond to the specified values, replace the ECM.

5. If all circuits test normal, test or replace the engine coolant thermostat heater.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.