Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P0597 Thermostat Heater Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Heating resistor in the thermostat open
Connector at the thermostat loose or corroded, coolant in the connector
Broken wire or missing supply (fuse, relay)
Engine module driver

Symptoms

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

Repair estimate

DifficultyMediumDIY possible
Parts and labour€120–600
Time1–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

map controlled thermostatthermostat heaterheater wiringengine control module

Related codes

P0598P0599P0128P2181P0217

References: gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.