EngineLightCodes
Powertrain code

P0597 Thermostat Heater Control Circuit/Open

Severity
Fix soon
Typical repair cost
$130–$660
Do it yourself
Possible, medium
Shop time
1–3 hours

A map-controlled thermostat is a wax thermostat with a built-in heating resistor (Valeo: about 10 Ω).

How the engine computer detects it

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.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Check engine light on (after two trips)
  • Coolant temperature higher than usual under load
  • Audi/VW: coolant warning and engine speed limit possible

Common causes

  1. Heating resistor in the thermostat open Most likely
  2. Connector at the thermostat loose or corroded, coolant in the connector Possible
  3. Broken wire or missing supply (fuse, relay) Possible
  4. Engine module driver Less likely

How to diagnose P0597

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: map controlled thermostat, thermostat heater, heater wiring, engine control module.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Vehicles that report P0597 most

VehicleYearsReportsMedian miles
Chevrolet Volt2016–20184—

Counts of owner complaints to the NHTSA that mention P0597 (10 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.

Reading the code

P
Powertrain
0
Generic (SAE) code
5
Vehicle speed, idle control and auxiliary inputs
97
Specific fault

Questions drivers ask

Can I drive with code P0597?

Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.

Will my car pass an emissions inspection with P0597?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Will P0597 clear by itself?

The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.

Can I fix P0597 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.

Often reported together

Codes that owners mention in the same NHTSA complaints as P0597. They can point to a shared cause, so it's worth checking them together.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.