Trouble CodeFault LocationProbable Cause
P0118 Engine coolant temperature (ECT) sensor -high inputCoolant thermostat, wiring open up circuit/short come positive, earth wire defective, ECT sensor

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What Does password P0118 Mean? video

P0118 Engine Coolant Temperature Sensor Circuit hello Voltage: diagnostic checks for a resistance equivalent to a really low engine coolant temperature. Engine control module (ECM) or PCM (powertrain control module) gives 5 V come the ECT sensor signal circuit and also a ground for the low reference circuit. Diagnostic checks for an open, brief to soil or one intermittent circuit condition between the ECM and ECT sensor. The engine should run because that a calibration period of time prior to the engine coolant temperature sensor high examine is executed. This permits the engine time to warmth the coolant up beyond the bottom of the sensor range in cold ambient conditions. If permit conditions space met and the resistance of the sensor is higher than a calibration because that a duration of time the test will fail and the password sets.

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The ECT (Engine coolant temperature) sensor is supplied to measure up the engine temperature and is threaded in the engine coolant jacket and also in direct call with the engine coolant. The ECT is a thermistor, (resistance is inversely proportional come temperature) the resistance the a thermistor decreases together the temperature increases. Together the resistance decreases, the voltage input come the engine computer alters with the engine temperature, which provides engine coolant temperature information. Short coolant temperature has high resistance and high coolant temperature has actually low resistance (High Voltage/Low Temp , short Voltage/High Temp ), which can be showed with a digital voltmeter.

Figure 1 Voltage Divider Network

The ECT circuit is a variable ground, which supplies a voltage divider network (Figure 1) whereby the voltage is divided between the sensor input and also a sensor ground inside the computer (Black Box). The computer system provides the 5-volt referral signal to the ECT Sensor (Figure 1). When cold, the sensor provides high resistance, which the computer system reads as high signal voltage. Together the engine warms up, the THERMISTOR sensor resistance becomes lower and the signal voltage drops, so the is the difference. You execute not should know all of the inner functions of the computer, just that once you check voltage ~ above the yellow wire (Figure 1) and the engine is cold, you need to read high voltage in ~ 3-5 volts and also at normal operating temperature the signal voltage should be low around 0.47-1.45 volts, watch the below table:

Vehicle MakerVoltage Cold (volts)Voltage warm (volts)
GM Pull-up Resistor4.950.75
Chrysler Pull-up Resistor4.701.83
Chrysler ECM Pull-up Resistor4.201.45
Vehicle MakerResistance Cold (Ohms)Resistance hot (Ohms)
European Bosch6,500230

The ECT has a really high resistance as soon as cold and low resistance when warm (see table). This kind of thermistor is called an NTC (negative temperature coefficient), i beg your pardon is opposite come the case with many other electric components. So, if the coolant sensor has actually a bad connection (high resistance) in ~ the wiring connector, the computer will check out a higher voltage signal and also would it is provided a richer-than-normal fuel mixture based on the resistance of the coolant sensor and set one of the ECT diagnostic problem codes (DTC).


Figure 2 step Up Resistor ECT Circuit

Some auto manufacturers usage a step-up resistor to increase the variety of the ECT sensor (Figure 2). Number 2 shows an example of a 2-step ECT circuit showing that when the coolant temperature is low, the computer uses a 5-volt reference signal come the ECT sensor v a higher resistor compared to once the temperature is higher.

P0118 will collection if the voltage measured by the engine computer system (ECM/PCM) is higher due come high resistance (Low Voltage/High Temp ) prefer a disconnected ECT sensor. The engine computer system checks because that a resistance equivalent to a really low engine coolant temperature. The inspect is enabled whenever the ECM is powered. If the resistance the the sensor is better than a calibration for a period of time P0118 will set.

What are the common causes of password P0118 ?

Bad connection at the sensorShort in the voltage feed in between the sensor and also ECM/PCMDefective ECM/PCM (not likely)Defective ECT sensor (shorted internally)

What Happens once DTC P0118 Sets

Cooling fans will be commanded ONEngine Coolant Temperature Gauge is inoperativeAC compressor will be commanded OFF

Conditions for setting DTC P0118

ECM/PCM detects the the ECT is chillier than −38°F (−39°C) for much more than five seconds.Ignition is on or engine is to run for more than 10 seconds.Engine operation time is much less than 10 seconds when IAT Sensor 1 is warmer than –7°C (19°F).DTC P0118 runs consistently within the enabling conditions.

What room the symptom of code P0118 ?

MIL (Malfunction Indicator Lamp) How execute you troubleshoot code P0118 ?

Tools Needed: Scan tool (rented or purchased, about $250), If you have actually a laptop PC, a good choice is for $247, DMM (Digital Multimeter), and access to an online business information internet site favor

Scan tool Testing

If not already done, walk to one online service information provider prefer ALLDATA or Mitchell On-Demand or equivalent and also download the P0118 diagnostic procedure and diagnostic circuit check. Additionally do a TSB (Technical service Bulletin) find for worries related come DTC P0118.You will have actually the MIL irradiate on, therefore verify the the DTC P0118 is save on computer or activeMaximum difference between the 2 readings have to be 10°F (5°C).If the above test works, the connector and also wiring space most likely okay, inspect the ECT sensor for resistance and also compare to the really engine temperature graph in step 7 below.If the wiring does not work as shown in action 4 third bullet, inspect for an open up in the yellow signal cable or a disconnected or corroded ECT sensor connector, see figure 1 or the download wiring diagram.Testing Engine Coolant Temperature SensorCheck the radiator reservoir bottle is full and radiator itself is filled to top.

NOTE: Be sure that the radiator is cool prior to removing the radiator lid to prevent being scalded by hot coolant. Regular operating temperature different with automobile make and model. Part vehicles room equipped with a thermostat v an opened temperature of 180°F (82°C), whereas various other vehicles use a thermostat that is 195°F (90°C) or higher. Before replacing the ECT sensor, be certain that the engine is operating at the temperature mentioned by the manufacturer. Most manufacturers recommend checking the ECT sensor after the cooling fan has cycled twice, describe a completely warmed engine.

ECT sensor must be submerged in coolant to be able to indicate the appropriate coolant temperature.Proper pressure preserved by the radiator cap. If the radiator cap is defective and also cannot enable the cooling mechanism to come to be pressurized, waiting pockets might develop. These air pockets could cause the engine to operate at a name is than-normal temperature and also prevent appropriate temperatureCheck the antifreeze–water mixture. Many OEMs (Original tools Manufacturers) recommend a 50/50 mixture that antifreeze and also waterCheck for suitable operation the the cooling fan. If the cooling fan does not run correctly, the engine might overheat.Go to an online business information provider choose ALLDATA or Mitchell On-Demand or equivalent and download the Temperature versus Resistance – Engine Coolant Temperature Sensor table because that ECT for the car you space working on.With the Ignition OFF, disconnect the harness connector in ~ Engine Coolant Temperature Sensor.If no within the specified range replace the ECT sensor.If within the specified range, check for limitless resistance in between each terminal and also the sensor housing.If less than infinite resistance, replace the ECT sensor.If boundless resistance is okay, inspect the computer and consult a experienced technician or service shop.

Optional in-depth ECT Circuit trial and error if every Else Fails

Go come an online organization information provider prefer ALLDATA or Mitchell On-Demand or equivalent and download the wiring diagram for ECT because that the automobile you room working on.Study the wiring diagram and using a highlighter trace the circuit native the ECM (Engine regulate Module) or PCM (Powertrain control Module) come the ECT.With the ignition OFF and also all vehicle systems OFF, disconnect the exploit ECT connector.Test because that  ohms in between the low referral terminal and ground.If 5 ohms or greater, revolve the ignition OFF, disconnect the exploit connector at the ECM or PCM.Test for less than 2 ohms in the low referral circuit end to end, evaluation wiring diagram.If 2 ohms or more, fix the open/high resistance in the circuit.If much less than 2 ohms, the ECM can be defective.If less than 5 ohms through the ignition ON.If warmer 보다 −38° F (−39° C) v ignition OFF, disconnect the harness connector in ~ the ECM/PCM.Test for boundless resistance in between the signal circuit terminal  and ground.If much less than limitless resistance, fix the quick to floor on the circuit.If unlimited resistance, the ECM may be defective.If cooler than −38° F (−39° C)Install a 3 A unify jumper wire between the signal circuit terminal B and the low recommendation circuit terminal. If 300° F (149° C) or colderIgnition OFF, disconnect the harness connector at the ECM/PCMIf 1 volt or greater, fix the brief to voltage top top the circuit.If less than 1 volt, revolve the ignition OFF and test for much less than 2 ohms in the signal circuit finish to end.If 2 ohms or greater, fix the open/high resistance in the circuit.If much less than 2 ohms, the ECM is defective.If warmer than 149° C (300° F): test or change the Engine Coolant Temperature Sensor.

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DTC P0118 Diagnostic Tips

Coolant temperature gauge will screen full cold when an ECT DTC set’s.After beginning the engine, the ECT sensor temperature should rise steadily, then stabilize ~ the thermostat opens.

DTC P0118 Scan device Data Parameters