P0597Thermostat Heater Control Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- A map-controlled thermostat is a wax thermostat with a built-in heating resistor (Valeo: about 10 Ω). Unheated it opens late, for hot running at part load; the engine module heats it by map under full load or towing so it opens earlier. CARB requires the thermostat to be monitored and the heater circuit counts as an output component. GM switches it to ground with a low-side driver and checks it every second, fault after 15 of 30 samples, type B; Hyundai/Kia/Genesis and VW/Audi use the codes as well. P0597 means the heater circuit is open – GM above 200 kΩ with the driver off. The thermostat then only works through its wax and opens late, so coolant runs hotter under load; Audi's 4.2 FSI also limits engine speed. Genesis (G80/G90 3.3 T, 3.8) replaced thermostats from an early production lot.
- What you may notice
- Check engine light on (after two trips)
- Coolant temperature higher than usual under load
- Audi/VW: coolant warning and engine speed limit possible
- Likely causes
- LikelyHeating resistor in the thermostat open
- PossibleConnector at the thermostat loose or corroded, coolant in the connector
- PossibleBroken wire or missing supply (fuse, relay)
- RareEngine module driver
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €120 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.