P0597🔧 Electronically controlled engine thermostat (cooling system)Stop and fix promptly

P0597: Thermostat Heater Control Circuit Open (Meaning, Causes, Fixes)

Reviewed 2026-10-23 · Based on 2 cited source(s)

What P0597 means

Some engines use a thermostat that the engine computer controls electronically instead of relying only on coolant temperature. OBD-Codes.com explains that the system uses temperature and load sensors, a computer program and a thermostat housing with a built-in electric heater, so the computer can run the engine warmer at part throttle for fuel economy and emissions, and cooler under load for power. P0597 is set when the control voltage to that heater circuit is missing (an open circuit). RepairPal words the trigger more broadly, saying the PCM (engine computer) sets the code when it detects an incorrect signal from the thermostat. It is a generic code, but OBD-Codes.com says only a small number of manufacturers use this type of thermostat, mostly German brands such as BMW, Mercedes, Audi, Mini, Volkswagen, Opel and Jaguar. The OBD-Codes.com forum also has P0597 threads from Chevy Cruze and Aveo owners, so it is not limited to German cars. Related codes in the same family are P0598 (circuit low) and P0599 (circuit high); OBD-Codes.com treats all three with the same diagnosis.

Severity: can I keep driving?

Stop and fix promptly

Watch your temperature gauge and get it checked promptly. RepairPal rates P0597 Urgent, meaning immediate action is necessary. OBD-Codes.com is milder, saying you are unlikely to notice any difference in how the car drives, but warns the gauge may read abnormally high if the thermostat failed partly closed. OBD-Codes.com also says low coolant can set this code. If the gauge climbs toward hot, steam appears or the coolant is low, pull over and shut the engine off rather than risk overheating damage.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Loose or corroded electrical connector at the thermostat, which OBD-Codes.com says is one of the usual causes (OBD-Codes.com, RepairPal lists wiring issues)
  2. Failed electronically controlled thermostat (OBD-Codes.com, RepairPal)
  3. Open or short in the wiring between the engine computer and the thermostat (OBD-Codes.com, RepairPal)
  4. Low coolant or a coolant leak, which OBD-Codes.com says can overheat the electronic thermostat and set the code (OBD-Codes.com only)
  5. Failed engine computer (PCM, called the Motronic unit on many German cars), which OBD-Codes.com calls the least likely cause (OBD-Codes.com, RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Check the coolant level with the engine cold. OBD-Codes.com says low coolant can set this code, so find and fix any leak first.
  2. Unplug the thermostat's electrical connector and inspect it. OBD-Codes.com suggests removing corrosion, applying electrical grease and making sure the connection is tight.
  3. Clear the code and see whether it returns after a drive.
  4. With your service manual's pin layout and values, measure the thermostat heater's resistance at its connector. OBD-Codes.com says to replace the thermostat if the resistance is out of range; specifications vary by manufacturer and engine.
  5. OBD-Codes.com also describes checking the voltage on the computer side of the harness with the engine running, using an infrared thermometer to note engine temperature. These values vary by vehicle, so follow your manual.
  6. If you don't have the wiring information or tools, OBD-Codes.com recommends a shop with access to that data, saying it is a simple diagnosis with the right tools.

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • The temperature gauge is reading high or the engine is overheating
  • You don't have the pin layout, resistance values or a multimeter for your vehicle
  • The code returns after a new thermostat and a repaired connector
  • Your coolant keeps dropping and you can't find the leak
  • The cooling fans run all the time

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0597?

Carefully, and not for long. RepairPal rates it Urgent, while OBD-Codes.com says you may not notice a difference. Watch the temperature gauge, and stop driving if it reads high or the coolant is low.

What is a thermostat heater?

On engines with an electronically controlled thermostat, the thermostat housing has a small electric heater that the engine computer uses to open the thermostat when it wants the engine to run cooler. OBD-Codes.com says this improves fuel economy at part throttle and power under load.

What's the difference between P0597, P0598 and P0599?

All three refer to the electronically controlled thermostat's heater circuit. P0597 is circuit open, P0598 is circuit low and P0599 is circuit high. OBD-Codes.com uses the same diagnosis for all three.

How much does it cost to fix P0597?

Neither source gives a repair cost for P0597. It can be as simple as cleaning a corroded connector or topping up coolant, or as involved as replacing the thermostat housing, so diagnose it first.

Sources

  1. OBD-Codes.com: P0597 Thermostat Heater Control Circuit Open
  2. RepairPal: P0597 Thermostat Heater Control Circuit/Open (rated Urgent)

Last reviewed 2026-10-23. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.