CoolingGeneric OBD-II codeUrgency: Garage soon
Code P0118: coolant temperature sensor: high signal
P0118 means: engine coolant temperature sensor circuit: input high.[1][2] The engine ECU has detected that the signal voltage of the coolant temperature sensor (ECT) is too high. It is an NTC sensor, whose resistance falls as it heats up, and its voltage falls with it: in a test by Samarins, the sensor gave 3.96 V with the engine cold and 0.988 V with the engine hot. That is why a very high voltage is equivalent to a "very cold" engine, and it is what happens when the circuit opens (broken sensor, broken wire or loose connector): the ECU ends up reading an extreme temperature, for example −40 °C.[1][2][3][4][5]
What code P0118 means
The engine ECU has detected that the signal voltage of the coolant temperature sensor (ECT) is too high. It is an NTC sensor, whose resistance falls as it heats up, and its voltage falls with it: in a test by Samarins, the sensor gave 3.96 V with the engine cold and 0.988 V with the engine hot. That is why a very high voltage is equivalent to a "very cold" engine, and it is what happens when the circuit opens (broken sensor, broken wire or loose connector): the ECU ends up reading an extreme temperature, for example −40 °C.[1][2][3][4][5]
While it is not receiving reliable data, the ECU does not know what temperature the engine is at. In the workshop documentation for the 2001 Saab 9-3, for example, the fault is logged when the voltage exceeds 4.91 V for more than a second (short circuit to positive or open circuit) and the ECU calculates a substitute temperature from the intake air temperature at start-up. In that car, the radiator fans also run continuously and the temperature gauge shows wrong values.[6]
It is a generic OBD-II code (it starts with P0), not specific to one make, so its definition is the same on any car; what changes from one engine to another is the most likely cause.[7]
Original definition (SAE J2012): Engine Coolant Temperature Circuit High Input[1][2]
Causes of P0118
From most to least likely, according to the sources.
- 1Faulty coolant temperature sensor, normally with the internal thermistor open: Carista identifies it as the most common cause.[1][5][6][8][9]
- 2Poor electrical connection at the sensor: loose or unplugged connector, corroded terminals (water in the connector is one cause of corrosion), broken or chafed signal wire, or a problem in the sensor's earth circuit.[1][3][5][6][8][9]
- 3Low coolant level or air pockets in the system, which leave the sensor tip uncovered and can distort its signal.[3]
Symptoms
- Engine warning light on in the instrument cluster.[1][6][8]Engine warning light: faults that cause it
- Difficulty starting, hot or cold, or the engine does not start.[1][5][8][9]Hard to start: faults that cause it
- Black smoke from the exhaust, due to excess fuel.[1][5]Black smoke: faults that cause it
- Increased fuel consumption.[1][4][5]Uses more fuel: faults that cause it
- Radiator fans running continuously.[3][6][8]
- Temperature gauge with wrong or erratic readings.[3][6][8]
- Rough idle, or idle at a higher speed than normal.[4][9]Vibrations: faults that cause it
- The air conditioning may stop working.[3][6]
How to diagnose P0118
In order: from the most likely and cheapest to check to the most expensive.
- 1Read the stored codes and the freeze-frame data: a value of −40 at the moment of the fault indicates that the sensor circuit was open. With the engine cold (after sitting overnight), compare the coolant temperature with the intake air temperature and the ambient temperature in the live data: they should be almost the same (KFZ Dietrich talks of ±5 °C after more than 8 hours standing).[3][5]
- 2Check the coolant level and that there is no air in the system.[3]
- 3Inspect the sensor, the connector and the wiring: wear, corrosion, water in the connector, damaged terminals or wires that rub.[1][3][4]
- 4Wiggle the wiring harness and the connector at several points while watching the data on the diagnostic tool: a sudden change in voltage points to the area of the fault.[3][6]
- 5Jumper test: with the sensor disconnected, join the two terminals of the connector with a wire; the diagnostic tool should read more than 120 °C. If it does not, there is a power supply or earth problem in the wiring.[1]
- 6Use a multimeter to measure the supply voltage at the connector (about 5 V with the ignition on), the sensor's resistance at different temperatures against the manufacturer's table, and the continuity and insulation of the wire to the ECU.[3][4][5]
- 7If the sensor's resistance is not correct, replace it; if the fault is in the wiring or the connector, repair it.[1]
Can I keep driving with P0118?
Garage soon
The sources do not agree. Autodoc asks for it to be resolved immediately: the car may not start or may start with difficulty and, if it is not fixed, it may suffer serious engine damage. KFZ Dietrich considers short journeys to the garage acceptable as long as the engine runs well and the warning light is not flashing, and Carista classes it as medium severity. To be safe, it is best checked soon.[1][5][8]
Documented faults related to P0118
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
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.
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.
- Critical severityFrequency: Occasional1.6 GDi híbrido (Kappa)Main relay of the power relay assembly (overheating and fire risk)Yes, on the first units: Hyundai and Kia recalled 2016–2018 Ioniq and Niro hybrids and plug-in hybrids because the main relay that connects the high-voltage battery could come loose, overheat and, in the worst case, cause a fire.
- Critical severityFrequency: Occasional1.6 GDi híbrido (Kappa)Clutch hydraulic actuator (HCA): leak or moisture with risk of short circuit and fireYes, this is the most documented hybrid system fault: the hydraulic actuator that engages the combustion engine with the hybrid assembly has had two recalls (2018 for a leak on the Niro and 2025 for moisture in its electronic board on the Niro, Ceed and XCeed PHEV), with a risk of short circuit and fire.
- 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.
- 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.
Frequently asked questions
Can I drive with code P0118?
The sources do not agree. Autodoc asks for it to be resolved immediately, because the car may not start or may start with difficulty and, if it is not fixed, it may suffer serious damage. KFZ Dietrich considers short journeys to the garage acceptable as long as the engine runs well and the warning light is not flashing, but warns that if the light flashes or there is a loss of power or limp mode you must stop. The sensible course is not to prolong use of the car and to have it checked soon.[1][5]
Does P0118 mean the engine is very hot?
Not necessarily: "high" refers to the electrical voltage of the signal. On an NTC sensor the voltage falls as it heats up, so a very high voltage is equivalent to a "very cold" engine, and it is what happens with an open circuit: Autodoc talks of a reading below freezing, Samarins of −40 in the freeze-frame data and KFZ Dietrich of extreme cold. Carista, on the other hand, describes it as an "impossibly hot" reading, and Ross-Tech, for VW group cars, speaks of a "signal too high" but cites an electrical signal that is "too low". The most reliable course is to use the diagnostic tool to see what temperature the ECU is actually reading.[1][3][5][8][9]
Why do the radiator fans run continuously?
When the ECU does not trust the temperature reading, some cars run the radiator fans continuously as a protective measure: Carista and Saab's workshop manual state this for this code, and Samarins for sensor faults in general. KFZ Dietrich describes this behaviour in connection with P0117.[3][5][6][8]
How does P0118 differ from P0117?
Both are faults in the coolant temperature sensor circuit. P0117 is "circuit low": the signal voltage sits close to 0 V, which the ECU reads as an extremely high temperature and responds with protective measures; it is usually due to a short circuit to earth. P0118 is "circuit high": the voltage sits close to the reference voltage (4.8–5 V), typical of an open circuit, which the ECU reads as extreme cold and enriches the mixture, with a risk of flooding the engine when hot.[3][5]
Will I pass the MOT with code P0118?
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.[10]
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.
- Código de avería P0118 - guía paso a paso para su diagnóstico y resoluciónAutodoc Club · Technical documentation · consulted 2 October 2026 · in Spanish
- P0118 — Engine Coolant Temperature Circuit High InputThe Automotive Technician (TaT) · Technical documentation · consulted 2 October 2026
- Engine coolant temperature sensor: how it works, symptoms, problems, testingSamarins.com · Technical documentation · published 18 July 2021 · consulted 2 October 2026
- Checking the coolant temperature sensor – symptoms, cause of failure and troubleshootingHELLA · Manufacturer · consulted 2 October 2026
- P0117 vs. P0118: ECT-Sensor Kurzschluss und KabelbruchKFZ Dietrich (Kfz-Meisterbetrieb) · Other source · published 4 August 2026 · consulted 2 October 2026 · in German
- Saab 9-3 (9400) 2001, Trionic T7: P0118 Engine Coolant Temperature Sensor Circuit. Short to B+ / Open circuit.Saab WIS Online (manual de taller de Saab) · Technical documentation · consulted 2 October 2026
- On-board diagnosticsWikipedia · Other source · consulted 2 October 2026
- P0118: OBD-II code P0118 means the engine coolant temperature (ECT) sensor is reading impossibly hot — typically an open circuit or a failed sensor.Carista · Technical documentation · consulted 2 October 2026
- 16502/P0118/000280 - Engine Coolant Temperature Sensor (G62): Signal too HighRoss-Tech Wiki · Technical documentation · consulted 2 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