P0597 – Thermostat Heater Control Circuit / Open (OBD2)
P0597 means "Thermostat Heater Control Circuit / Open". The control unit sees an open circuit: the electrical connection to the map-controlled thermostat heater is interrupted, so no current can flow when the component is commanded or read.
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P0597 quick summary
| Fault code | P0597 |
|---|---|
| Meaning | Thermostat Heater Control Circuit / Open |
| System | Powertrain (Engine & Transmission) |
| Vehicles | Generic OBD2 |
| Severity | Low |
| Can I drive? | Yes. The thermostat still opens mechanically. Watch the temperature on long climbs and towing. |
| Repair cost | €60 – €500 |
How the map-controlled (electric) thermostat works
Some engines use a thermostat with an electric heating element, so the control unit can open it earlier under load; these codes cover the heater's control circuit.
A map-controlled thermostat works like a normal wax thermostat but has a built-in heating element. When the engine is under high load, the control unit heats the wax so the thermostat opens earlier and the engine runs cooler; at part load it keeps the engine warmer for efficiency.
Codes P0597–P0599 report an open, low or high fault in the heater control circuit. The thermostat still works mechanically, but the engine runs at a higher temperature under load.
The heater is part of the thermostat housing, so a failed heater usually means replacing the thermostat. Corroded connectors are also common because the connector sits near the coolant.
On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16981 (P0597). Both numbers mean the same fault.
Symptoms of P0597
- Check Engine light on
- Engine temperature slightly higher under load
- Usually no driving symptoms
- Sometimes coolant temperature codes
Most common causes of P0597 (most likely first)
Mechanic's Pro Tip
Map-controlled thermostats are often replaced together with the coolant and the housing seal – use the manufacturer's coolant and the correct bleeding procedure.
1.Unplugged, loose or corroded connector
Most likelyOften after previous repair work in the area.
2.Broken wire in the harness
Typical at bends, near the engine mounts and where the harness rubs on brackets.
3.Burnt-out winding or internal break in the map-controlled thermostat heater
4.Failed heating element in the thermostat
5.Wiring fault
6.Blown fuse
7.Control unit driver fault
Step-by-step diagnostic guide
- 1
Read codes
Read all codes and check for related coolant temperature codes.
- 2
Measure resistance and continuity
Unplug the map-controlled thermostat heater and measure its resistance across the terminals. An infinite (OL) reading confirms an internal break. If the component is fine, check each wire back to the control unit for continuity.
Multimeter: Solenoids and heaters typically read a few ohms to a few dozen ohms; "OL" means open. Wire continuity: below about 1 Ω.
- 3
Inspect the connector
Check the thermostat connector for corrosion and coolant.
- 4
Measure the heater
Measure the heater resistance at the thermostat.
Multimeter: Typically about 10–20 Ω; 'OL' means the heater is open.
- 5
Check supply and control
Check the supply voltage and the control wire from the control unit.
- 6
Replace and bleed
Replace the thermostat (with housing if integrated), refill with the correct coolant and bleed the system.
Frequently asked questions
Can I keep driving with P0597?
Yes. The thermostat still opens mechanically. Watch the temperature on long climbs and towing.
How much does it cost to fix P0597?
Typical repair costs are 60 € – 500 €, depending on the cause and the vehicle. The most common fixes are: unplugged, loose or corroded connector; broken wire in the harness; burnt-out winding or internal break in the map-controlled thermostat heater. Always confirm the cause with the tests above before buying parts.
Can I drive with a thermostat heater code?
Yes. The thermostat still opens at its mechanical temperature; only the electronic control is lost.
Can I replace only the heating element?
Usually not – it is built into the thermostat.
What is the difference between P0597 and similar codes?
P0597 belongs to a group of codes for the same component that differ in the type or location of the fault: P0598 – Thermostat Heater Control Circuit Low; P0599 – Thermostat Heater Control Circuit High. The tests on this page apply to the whole group; the type of fault tells you where to start.
Related fault codes
This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.