DTC Descriptors
DTC P0117: Engine Coolant Temperature (ECT) Sensor Circuit Low VoltageDTC P0118: Engine Coolant Temperature (ECT) Sensor Circuit High Voltage
Diagnostic Fault Information
Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance |
|---|---|---|---|---|---|
ECT Sensor Signal | P0117 | P0118 | P0118 | P0118 | P0116, P0125, P0128 |
Low Reference | -- | P0118 | P0118 | P0118 | P0125, P0128 |
Typical Scan Tool Data
Circuit | Normal Range | Short to Ground | Open | Short to Voltage |
|---|---|---|---|---|
ECT Sensor Signal | -39 to +120°C (-38 to +248°F) | 150°C (302°F) | -40°C (-40°F) | -40°C (-40°F) |
Low Reference | -- | -- | -40°C (-40°F) | -40°C (-40°F) |
Circuit/System Description
The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT signal circuit and supplies a ground to the low reference circuit.
Conditions for Running the DTC
P0117
| • | The engine is running for more than 10 seconds. |
| OR |
| • | The engine run time is less than 10 seconds when the intake air temperature (IAT) is less than 50°C (122°F). |
| • | This DTC runs continuously within the enabling conditions. |
P0118
| • | The engine is running for more than 10 seconds. |
| • | The IAT is more than 0°C (32°F). |
| • | This DTC runs continuously within the enabling conditions. |
Conditions for Setting the DTC
P0117
The ECM detects that the ECT is more than 149°C (300°F) for more than 5 seconds.
P0118
The ECM detects that the ECT is less than -39°C (-38°F) for more than 5 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
- Turn OFF the ignition.
- Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling .
- Turn ON the ignition, with the engine OFF.
- Use the scan tool to verify the proper operation of the engine cooling system fans.
- Turn OFF the ignition.
- Verify the proper heat range, and the operation of the thermostat. Refer to Thermostat Diagnosis .
Caution: Under pressure, the temperature of the solution in the radiator can be considerably higher, without boiling. Removing the radiator cap while the engine is hot (pressure is high), will cause the solution to boil instantaneously, with explosive force. The solution will spew out over the engine, fenders, and the person removing the cap. Serious bodily injury may result. Flammable antifreeze, such as alcohol, is not recommended for use at any time. Flammable antifreeze could cause a serious fire.
Circuit/System Testing
P0117
- Turn ON the ignition, with the engine OFF.
- Disconnect the ECT sensor.
- Observe the ECT Sensor parameter with a scan tool.
| ⇒ | If the ECT Sensor parameter is less than -39°C (-38°F), then replace the ECT sensor. |
| ⇒ | If the ECT Sensor parameter is more than 149°C (300°F), then test the ECT sensor signal circuit for a short to ground. |
| ⇒ | If the ECT sensor signal circuit tests normal, replace the ECM. |
P0118
- Turn ON the ignition, with the engine OFF.
- Disconnect the ECT sensor.
- Measure for the proper range of 4.9-5.2 volts between the ECT sensor signal circuit and a good ground with a DMM.
- Turn OFF the ignition, and all electrical accessories. Allow sufficient time for all of the control modules to power down before taking a resistance measurement.
- Measure for a proper value of less than 5 ohms of resistance between the ECT low reference circuit and a good ground.
- Turn ON the ignition, with the engine OFF.
- Observe the ECT Sensor parameter while connecting and disconnecting a 3-amp fused jumper wire between the ECT sensor signal and low reference circuits. This should cause the ECT Sensor parameter to toggle between the upper and lower temperature limits.
| ⇒ | If the voltage is less than 4.9 volts, test the ECT sensor signal circuit for a high resistance or an open circuit. If the circuit tests normal, replace the ECM. |
| ⇒ | If the voltage is more than 5.2 volts, test the ECT sensor signal circuit for a short to voltage. If the circuit tests normal, replace the ECM. |
| ⇒ | If the resistance is more than 5 ohms, test the low reference circuit for a high resistance, or an open circuit. If the circuit tests normal, replace the ECM. |
| ⇒ | If the ECT Sensor parameter does not toggle, replace the ECM. |
| ⇒ | If the ECT Sensor parameter does toggle, then test the ECT sensor signal circuit for a short to another 5-volt reference circuit. |
| ⇒ | If the ECT sensor signal circuit is not shorted to another 5-volt reference circuit, then replace the ECT sensor. |
Component Testing
Measure and record the resistance of the ECT sensor at various ambient temperatures, and then compare those measurements to the Temperature vs Resistance Table. Refer to Temperature Versus Resistance .
Repair Instructions
Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
