CoolingGeneric OBD-II codeUrgency: Monitor
Code P0597: thermostat heater: open circuit
P0597 means: thermostat heater control circuit: open circuit.[1][2] Some engines have an electronically controlled ("map-controlled") thermostat, with a heating element that the ECU activates so that it opens sooner and so regulates the engine temperature according to load. P0597 indicates that the ECU detects an open circuit (loss of continuity) in the control of that element.[1][2]
What code P0597 means
Some engines have an electronically controlled ("map-controlled") thermostat, with a heating element that the ECU activates so that it opens sooner and so regulates the engine temperature according to load. P0597 indicates that the ECU detects an open circuit (loss of continuity) in the control of that element.[1][2]
It is a generic OBD-II code. One source points out that if the heater fails the thermostat keeps working like a normal mechanical one, but the ECU loses the ability to force its early opening.[2]
Original definition (SAE J2012): Thermostat Heater Control Circuit Open[1][2]
Causes of P0597
From most to least likely, according to the sources.
- 1Faulty thermostat heating element (open circuit).[1][2]
- 2Wiring between the thermostat and the ECU that is damaged, burnt or cut, or a loose or corroded thermostat connector.[1][2]
- 3Blown fuse in the heater circuit.[2]
- 4Faulty coolant temperature sensors.[1]
- 5Fault in the ECU itself: it is rare and should be ruled out last.[1][2]
Symptoms
- Engine warning light on; this is the most common symptom.[1][2]Engine warning light: faults that cause it
- Slightly higher consumption on the motorway, because the engine may run cooler than optimal.[2]Uses more fuel: faults that cause it
- Coolant temperature reading slightly different from normal, or fans running more often on some cars.[2]Overheating: faults that cause it
How to diagnose P0597
In order: from the most likely and cheapest to check to the most expensive.
- 1Read the codes and check whether there are other coolant temperature codes, which could indicate a thermostat or sensor problem.[1]
- 2Visually inspect the thermostat connector (damage, corrosion, disconnection) and the wiring to the ECU.[1][2]
- 3Check the heater circuit fuse.[2]
- 4Measure the heater resistance at the thermostat terminals: a healthy heater reads a few ohms and an open one gives no continuity.[2]
- 5Check the 12 V supply at the heater with the ignition on and the earth continuity to the ECU.[2]
Can I keep driving with P0597?
Monitor
One of the sources indicates that driving is normally not affected, because the thermostat keeps working mechanically; it should be repaired to turn off the warning light and restore thermal management. Other code pages give it more severity, so if signs of overheating appear, stop and check the coolant.[2]
Documented faults related to P0597
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
Faults in which this code appears
Thermostat and cooling system: the most serious faults by engine and car
- High severityFrequency: CommonBMW M54Thermostat and water pump failureThe M54's thermostat, housing and water pump contain plastics that become brittle and fail. If left unattended, overheating can warp the aluminium cylinder head. It is advisable to replace them together.Appears at around 129,000 km
- High severityFrequency: CommonBMW M54Cracked expansion tank and coolant leakThe plastic expansion tank degrades over the years and eventually cracks. It is cheap compared with the cost of overheating an M52/M54, and age matters more than mileage.
- High severityFrequency: CommonPorsche V8 and V6 (Cayenne and Panamera)Cracked plastic coolant pipes on the Cayenne V8The first Cayenne V8s (the 4.5) have plastic coolant pipes under the intake manifold that crack with age and cause coolant loss; Porsche switched to aluminium around 2006-2007. A Canadian workshop says it also affects the later 4.8.
- High severityFrequency: Common1.4/1.6 VTiFragile water pump (and expansion tank or heat exchanger, depending on displacement)Yes: fiches-auto.fr describes a fragile water pump in both the 1.4 VTi (with an expansion tank prone to leaks) and the 1.6 VTi (with the heat exchanger), a cooling problem that the turbocharged 1.6 THP inherits from this naturally aspirated version.
Wiring, connectors and short circuits: the most serious faults by engine and car
- Critical severityFrequency: OccasionalBMW N62 / N63Additional turbo coolant pump with a risk of short circuit and fireIn 2011 BMW recalled 5, 6 and 7 Series, X5 and X6 models built between 2007 and 2011 because of the additional turbo coolant pump: moisture, a short circuit and, in extreme cases, a fire. In 2012 there was another campaign for a crack in the pump, with a more robust version.
- High severityFrequency: Occasional1.3 TCeBlown fuel pump fuseOn the Renault Captur II and Clio V with the 1.3 TCe engine, a 20-amp fuse can blow and leave the car without an engine. According to L'argus, in April 2021 this fault still had no factory fix; the official service centre's diagnosis includes checking, and sometimes replacing, the catalytic converter.
- High severityFrequency: OccasionalM264/M254Poorly tightened 48 V earth wiring in the mild-hybrid system (fire risk)Mercedes-Benz has issued several recalls (2022-2025) because the 12 V and 48 V earth connections of some cars with a 48 V system may be poorly tightened: resistance rises, the connection heats up and a fire cannot be ruled out. The official workshop checks them and repairs them if necessary in an hour or more.
- High severityFrequency: Occasional1.9 TDIUnit injector tappet wear and injector wiring damageOn the unit injector system, the tappets that operate the injectors can wear if the oil is not changed on time, and the injector wiring can be damaged by contact with oil, causing misfires or loss of power.
- Critical severityFrequency: CommonRover 75Seat SRS connector fault with airbag and seatbelt warning light onAuto Express warns that the Rover 75's seat SRS connector can cause the airbags to fail, and dealers were fixing it with revised connectors. The Dutch APK inspection puts the airbag or seatbelt fault warning among the most frequent defects across almost all series.
- Critical severityFrequency: OccasionalAlfa Romeo GiuliettaShort circuit from badly routed wiring that can prevent gear shifting (KBA campaign, 2010-2015)Yes: according to Germany's KBA, on Alfa Romeo Giulietta cars built between 2010 and 2015 inadequate cable routing could cause a short circuit and, as a result, gear-shift failure.
Engine sensors: the most serious faults by engine and car
- High severityFrequency: Occasional2.0 DTI and 2.2 DTIVP44 injection pump and air mass meter failureGerman Wikipedia documents recurring failures of the Bosch VP44 injection pump and the air mass meter in the early years of this engine. An owner testimony for this engine describes the pump being replaced at 192,500 km, at a cost the owner calls «prohibitive».
- Medium severityFrequency: Common2.0 TDIClogged particulate filter or faulty pressure sensorThe 2.0 TDI's particulate filter clogs if the car mostly makes short journeys, because it never gets to regenerate; sometimes the fault is just the differential pressure sensor. Cleaning it costs around €200 and replacing it, €800 to €3,000.Repair (garage): €800–€3,000
- Medium severityFrequency: Common1.4 and 1.6 8vCrankshaft position sensor failure (TDC sensor)The crankshaft position sensor (capteur PMH, or TDC sensor) appears repeatedly in the reliability sources for the Clio II, the Kangoo I and the Dacia Logan I with this engine, with hard cold starting or stalling as the main symptoms. It is a cheap part, but the failure can leave you stranded.
- Medium severityFrequency: Common1.4 and 1.6 16vCrankshaft position sensor failureThe crankshaft position sensor (capteur PMH) appears repeatedly in the reliability sources for almost every generation with this engine, with hard cold starting, stalling or the car cutting out unexpectedly. It is a cheap part, but the failure can leave you stranded.
Frequently asked questions
What does P0597 mean?
That the ECU does not detect continuity in the electronic thermostat's heating element circuit. The cause is usually the heater itself, the wiring or the connector.[1][2]
Can I drive with P0597?
According to one source, driving is normally unaffected because the thermostat still opens mechanically. Even so, it needs repairing; and if you notice the engine running too hot, do not carry on.[2]
Do I have to replace the whole thermostat?
On many engines the heater is built into the thermostat housing and is replaced as an assembly, but first rule out a faulty fuse, connector or wire, which are cheaper to fix.[1][2]
Will I pass the MOT with code P0597?
If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.[3]
Not sure what is wrong with your car? Describe what you notice in the symptom diagnosis or see all fault codes.
Sources
Every fact on this page links to its source. If you find an error, let us know.
- P0597 – Thermostat heater control system -circuit openTroubleCodes.net · Technical documentation · consulted 29 October 2026
- P0597: Thermostat Heater Control Circuit Opencarfaultcodes.co.uk · Technical documentation · consulted 29 October 2026
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish