Coolant Temp Sensor Resistance Chart: ECT Ohms & Voltage

Updated October 1, 2026. Reviewed by the Focusens Engineering Team.

Coolant temperature sensor resistance chart: published curves

Sources: GM table A is the Chevrolet Equinox service manual table "Temperature vs Resistance Values (Approximate)", reproduced on a third-party site. GM table B is a second ECT table in the same manual copy; the copy does not say which engine each table belongs to. Delphi's data sheet for coolant temperature sensor 12146312 follows table A within about 2% from −40 to 120 °C (3,555 Ω at 20 °C, tolerance ±7.4%). The Bosch column is from the Bosch Motorsport NTC M12 data sheet, nominal 2.5 kΩ ±5% at 20 °C. The Toyota column is from the Toyota 1GR-FE repair manual specification (third-party copy), which lists only the 20 °C and 80 °C points.

Not every coolant sensor sits near 2.5 kΩ at room temperature. Delphi's 15425529 coolant temperature sensor is 10 kΩ at 25 °C. A 10 kΩ reading at room temperature is therefore not proof of a fault until you know which curve the sensor follows. On GM table A, 10 kΩ corresponds to about −1 °C (30 °F); on GM table B, about −11 °C (12 °F).

What does an ECT sensor do?

The ECT sensor tells the engine control unit (ECU) how warm the coolant is. The ECU uses that signal to set fuel mixture, ignition timing, idle speed and cooling fan operation, and it uses it most heavily during a cold start, when the mixture is enriched. A wrong reading at −10 °C matters more to the engine than a wrong reading at 90 °C.

The ECT sensor and the dashboard temperature gauge sender are not always the same part. Toyota, for example, sells a separate water temperature sender gauge assembly that "sends a signal to the vehicle's gauge system". On many newer vehicles the gauge has no sender of its own: the ECM passes the coolant temperature to the instrument cluster over the CAN bus, as the Nissan Altima service information (third-party copy) describes. Before replacing a part because the gauge looks wrong, check which design the vehicle uses.

ECT sensor voltage: what the ECU reads

An ECT signal runs from near 5 V on a very cold engine to under 1 V when fully hot (0.29 to 0.98 V at 90 to 100 °C in the table below). Toyota sets P0118 above 4.91 V and P0117 below 0.14 V. The ECU does not measure resistance. It feeds 5 V through a resistor inside the control unit to the sensor's signal terminal and reads the voltage left across the sensor. Mitsubishi's service manual describes this path and gives the supply at the unplugged connector as "between 4.5 and 4.9 volts". A cold sensor has high resistance and a high voltage; a hot sensor has low resistance and a low voltage.

The voltage at a given temperature depends on the resistor inside the ECU, which varies by vehicle. Bosch says its NTC M12 "can be connected directly to most control units using a pull-up resistor (typically 1 or 3 kOhm)". With the Bosch curve and a 5 V supply, the ECU would see:

Calculated as 5 V × R / (R + pull-up) from the Bosch resistance values. These are our calculations, not a published voltage table; your vehicle's service manual gives the values for its own ECU.

The two columns show why a single "normal ECT voltage" does not exist: the same sensor at 20 °C reads 3.57 V on one ECU design and 2.27 V on another. The Toyota limits are from the Toyota RAV4 service manual, engine coolant temperature circuit (third-party copy, 2AZ-FE engine).

What do P0117 and P0118 mean? Open and shorted ECT readings

An open ECT circuit reads near 5 V and shows −40 °C (P0118); a short to ground reads near 0 V and shows 140 °C or higher (P0117), on Toyota's limits.

From the Toyota RAV4 service manual cited above. Toyota's Venza manual puts the short-circuit display at "Higher than 135°C (275°F)", so the exact figure varies by model. Mitsubishi uses similar limits: P0118 above 4.6 V and P0117 below 0.1 V, each held for 2 seconds. Both Toyota and Mitsubishi substitute a fixed 80 °C (176 °F) value while the fault is present, which is why an engine with a failed ECT sensor often runs, but runs poorly when cold.

The OEM wording of the related codes:

P0117 ("low input") means the voltage is too low, which the ECU reads as too hot. P0118 ("high input") means the voltage is too high, read as too cold. P0128 points away from the sensor: Mitsubishi sets it only after judging the ECT sensor normal, when coolant takes too long to reach 77 °C (171 °F), and lists a faulty cooling system or ECM as the likely causes.

Why a replacement sensor can pass a hot test and still read wrong when cold

Because ECT curves differ most when the engine is cold, a sensor with the wrong curve can look perfect on a warm engine. The table below takes the published Bosch resistance at each temperature and reads it back through GM table A, as an ECU calibrated to table A would.

Calculated by interpolating ln(R) against 1/T between adjacent rows of GM table A. The same error appears inside one manual: the midpoints of GM table B, calculated as (min + max) / 2, match the Bosch values to within half an ohm at every temperature both list, so a table-B sensor read through a table-A calibration gives exactly these errors.

At 90 °C the error is a third of a degree, so a check with the engine at operating temperature passes. At −20 °C the ECU believes the engine is about 11 °C warmer than it is and enriches the mixture less than it should. That pattern, normal when hot and rough or hard to start when cold, is a reason to compare the replacement's resistance at room temperature and in ice water, not only on a warm engine. The same kind of mismatch on motor drives is covered in our page on what a drive reads when the sensor type is wrong.

Symptoms of a bad coolant temperature sensor

The symptoms depend on which way the reading is wrong. A sensor that reads colder than the coolant but stays inside the valid voltage range, such as a wrong-curve part or a corroded connector, sets no code and makes the ECU run rich: poor fuel economy, a smell of fuel or black smoke. One that reads warmer leans the cold-start mixture, so the engine is hard to start and stumbles until warm. A hard open (P0118) or short (P0117) sets a code within 0.5 s on Toyota and 2 s on Mitsubishi, after which the ECU assumes 80 °C, so the engine runs as if already warm. A sensor that responds slowly can set P0116 (range/performance) or P0125. The cooling fan may run at the wrong times, and the gauge reads wrong only on vehicles where the gauge takes the ECT signal.

How to test a coolant temperature sensor

Remove or unplug the sensor only with the engine cold: a hot cooling system is under pressure and can scald, and coolant (ethylene glycol) is poisonous to children and pets, so catch any spill in a pan.

1. Note the temperature. With the engine cold and the sensor at ambient, measure the air or coolant temperature with a separate thermometer.
2. Disconnect and measure. Unplug the sensor and measure resistance across its two terminals. Compare with the manufacturer's table at that temperature. Toyota's 1GR-FE limit, for example, is 2.32 to 2.59 kΩ at 20 °C.
3. Cold check. In stirred ice water (0 °C) a GM table A sensor should read about 9,420 Ω, and a table B sensor 5,466 to 6,326 Ω (Bosch nominal 5,896 Ω). This is where a wrong-curve replacement shows up.
4. Heat test. Warm the sensor tip in stirred water at about 80 °C with a thermometer in the same water, and wait until the reading stops falling. Bosch gives its NTC M12 a response time "tau 63 in still water < 15 s", so five time constants, about 75 s, bring a sensor like it within 1% of its final value. The resistance should fall smoothly; Toyota's limit at 80 °C is 0.310 to 0.326 kΩ.
5. Check the supply. With the ignition on and the sensor unplugged, the signal terminal of the harness should read close to 5 V (4.5 to 4.9 V on the Mitsubishi example above). No voltage points to the wiring or the ECU, not to the sensor.
6. Compare with live data. On a cold engine that has stood overnight, the ECT reading on a scan tool should be close to the intake air temperature reading. Delphi rates its 12146312 at ±1.6 °C at 20 °C. If the intake air sensor is held to a similar tolerance, the two readings can differ by up to about 3.2 °C (1.6 + 1.6) from tolerance alone, so a larger gap after an overnight soak points at the sensor, its connector or its curve.

The bench steps above are the same as for any NTC thermistor. Our guide on how to test an NTC thermistor with a multimeter covers meter settings and lead handling, and how to detect a thermistor fault covers open, short and drift failures.

Where is the coolant temperature sensor located?

The ECT sensor has to sit in coolant, so it is threaded into a coolant passage, usually in or near the thermostat housing, in the cylinder head or in a coolant passage of the intake manifold. On the Toyota 1GR-FE it threads into the cylinder block and is tightened to 20 N·m (15 ft·lbf), per the specification cited above. Bosch's NTC M12 uses an M12×1.5 thread, a 19 mm wrench and 25 Nm. Many engines also carry a second sensor or a gauge sender close by, and the two are easy to confuse. The vehicle's service manual shows which one feeds the ECU.

ECT sensing elements and probes from Focusens

Focusens makes NTC thermistor elements and probes for sensor manufacturers. We do not sell replacement ECT sensors for specific vehicles, so for a repair, buy the part listed for your vehicle. Our automotive thermistor range includes the MF5A-3 epoxy NTC element, whose product page lists a 2.795 kΩ, B 4100 version among those used in automotive HVAC and coolant systems. 2.795 kΩ is the value GM table A gives at 25 °C; the product page does not state the reference temperature or how the B value is defined, so ask for the full resistance table. Our MF57 disc series data sheet lists "Temperature sensing and measuring in automobile cooling system" first among its typical applications. Because the curve is what the ECU depends on, send the OEM resistance table, or a sample, with an OEM inquiry so the element can be matched at the temperatures that matter, including the cold end. Our automotive thermistor guide covers where NTC and PTC parts are used in vehicles.

For the general background on NTC curves and B values, see how to select an NTC thermistor by R25 and B value and the NTC thermistor guide to B value and resistance curves. HVAC sensors follow different 10 kΩ curves, which are tabulated in our 10k thermistor chart, and our NTC vs PTC vs RTD vs thermocouple comparison covers the other sensor types.

Frequently asked questions

What is the normal resistance of a coolant temperature sensor at 90 °C?

On GM table A and the Bosch curve, a coolant temperature sensor reads about 240 Ω at 90 °C (194 °F): 241 Ω for GM table A and 243 Ω for Bosch. Other sensors differ, so check the maker's table.

What voltage should a coolant temperature sensor output?

A coolant temperature sensor's signal falls from near 5 V when very cold to under 1 V when fully hot. Toyota sets a fault code above 4.91 V (open circuit) or below 0.14 V (short). The voltage at a given temperature depends on the resistor inside the ECU, so use the vehicle's service data.

What happens if the coolant temperature sensor is unplugged?

An unplugged coolant temperature sensor looks like an open circuit. The signal goes to near 5 V, the ECU reads about −40 °C and sets P0118. Toyota and Mitsubishi then use a fixed 80 °C substitute value.

Is a 10 kΩ reading at room temperature normal for an ECT sensor?

A 10 kΩ reading at room temperature is not normal for the GM, Bosch or Toyota sensors on this page: they read 2.3 to 3.5 kΩ at 20 °C (68 °F), and the two GM tables give 2,796 Ω and 1,941 to 2,173 Ω at 25 °C (77 °F). A few coolant sensors are rated 10 kΩ at 25 °C, such as Delphi's 15425529, so check the part's own table. On GM table A, 10 kΩ means about −1 °C (30 °F); on GM table B it means about −11 °C (12 °F).

Is the ECT sensor the same as the temperature gauge sender?

The ECT sensor and the gauge sender are not always the same part. Some vehicles have a separate sender for the gauge; on many newer vehicles the ECU sends the ECT reading to the instrument cluster over the CAN bus.

Reviewed by the Focusens Engineering Team on October 1, 2026. Resistance values, voltage limits and code descriptions come from the OEM and sensor-maker documents linked beside each table; some are third-party copies of OEM manuals and are marked as such. The voltage table, the wrong-curve table and the 10 kΩ temperatures are our calculations from those published values, and the method is stated under each. The circuit diagram is an illustration and the engine-bay image is AI-generated. No reading on this page is a measurement taken on a Focusens part.