How to Fix a Chevy Cruze, Aveo, Sonic P0597, P0598 Thermostat Heater Circuit Code

Step by step instructions of how to diagnose and repair a GM 1.8L thermostat heater issue

Article contents

Parts Used



Required Tools

Recommended Tools

Testing Thermostat

Tip : Let engine cool for at least an hour before testing. If hot it can skew the testing results
  1. Locate and unplug the thermostat 2-wire connector - Watch
  1. Switch your multimeter to the ohm setting (How to Use an Ohm Meter)
  2. Place one multimeter lead on each terminal of the thermostat and take a resistance reading - Watch
Tip : Use terminal lead set to obtain a better connection on the thermostat pins

(Testing shown out of vehicle for visual purposes only)

  1. Compare reading to the specification of approximately 13-15 ohms
Tip : Ohm specification is based on our testing of multiple known good thermostats not OEM service information
  1. If thermostat is out of specification, it is faulty and requires replacement (Thermostat Replacement Procedure)

Checking Thermostat Control

  1. Locate the 2-wire thermostat connector and unplug it
  2. Hook up a test light in place of the thermostat, by attaching it to both terminals of the harness side connector - Watch
Tip : If terminal adapters are not available, the use of a paper clip or sewing pin may be required to probe the connector without damaging it
  1. Using a full functional scan tool, command the thermostat heater on while watching the test light. The test light should blink more rapidly as the commanded on-time percentage increases. - Watch
Tip : If a scan tool is unavailable, cycle the key while watching the test light. The light should illuminate briefly while the engine computer tests the circuit integrity. This method will also prove the computer’s ability to control the circuit.
  1. Using a scan tool, command the thermostat heater off (0% on time). If a scan tool is not available, turn off the key and wait 2-3 minutes till the computer shuts down and goes to sleep mode. Make sure the test light has gone out completely to confirm the circuit is not shorted
  2. If either of the tests above fail, check the heater circuit and engine computer for faults

Thermostat Replacement Procedure



Tip : Wait until the engine is cool or at ambient temperature before starting thermostat replacement
  1. Remove the coolant reservoir cap to ensure there is no pressure in the cooling system
  2. Unplug the thermostat connector and move it out of the way to avoid coolant contamination
  3. Using a pliers or hose clamp tool, compress the clamp securing the radiator hose to the thermostat housing, and move it down the hose past the housing outlet
Tip : A significant amount of coolant will drain from the hose upon removal, place a drain pan under vehicle to avoid spills.
  1. Carefully remove the coolant hose from the thermostat housing
  2. With a ratchet and a E10 external torx socket, remove the 4 thermostat bolts
  1. Remove thermostat from the engine


  1. Clean the sealing surface where the thermostat attaches to the engine. Make sure the surface is free of any residual coolant and defects such as sharp edges or corrosion
Tip : Check that the new thermostat has a properly installed gasket before installing
  1. Install the new thermostat and start all the bolts by hand to prevent cross threading
  2. Tighten the 4 thermostat bolts to 71-inch pounds
  3. Install the coolant hose on the thermostat outlet tube
  4. Using a pliers or hose clamp tool, compress the clamp on the coolant hose and relocate to original location on hose over the thermostat outlet
  5. Plug in thermostat and install any other components removed during thermostat replacement
  6. Fill coolant reservoir and bleed air from cooling system
  1. Start vehicle and check for any coolant leaks

For more information, questions, or help diagnosing your vehicle, contact the GoTech technical support team via phone or chat below.

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