P0118
DTC P0117 or P0118
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors
DTC P0117
- Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage
DTC P0118
- Engine Coolant Temperature (ECT) Sensor Circuit High Voltage
Diagnostic Fault Information
Typical Scan Tool Data
Circuit 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.
The following table illustrates the difference between temperature, resistance, and voltage:
Conditions for Running the DTC
P0117
* The engine is operating.
* The start up intake air temperature (IAT) is less than 72°C (161°F).
OR
* The start up intake air temperature (IAT) is greater than 72°C (161°F).
* The engine run time is more than 59 seconds.
* The DTC runs continuously once the above conditions are met.
P0118
* The ignition is ON or the engine is operating.
* The DTC runs continuously once the above condition is met.
Conditions for Setting the DTC
P0117
The ECM detects that the ECT is more than 140°C (284°F) for more than 4 seconds or a cumulative of 50 seconds.
P0118
The ECM detects that the ECT is less than -42°C (-43.6°F) for more than 4 seconds or a cumulative of 50 seconds. The scan tool is limited to -40°C (-40°F), so the diagnostic procedure uses -39°C (-38°F) to determine if there is an ECT condition.
Action Taken When the DTC Sets
DTC P0117 and P0118 are Type B DTCs.
Conditions for Clearing the MIL/DTC
DTC P0117 and P0118 are Type B DTCs.
Diagnostic Aids
* Test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor can result in a DTC or a driveability condition.
* If the vehicle has sat overnight, the IAT sensor and the ECT sensor values should display within 3°C (5°F).
* After starting a cold engine, the ECT sensor temperature should rise steadily, then stabilize after the thermostat opens.
* High resistance in the circuits of either the ECT or IAT sensor could set a DTC.
Circuit/System Verification
Engine idling for 1 minute. Observe the DTC information with a scan tool. DTCs P0117 and P0118 should not set.
Circuit/System Testing
1. Ignition OFF, disconnect the ECT sensor.
2. Ignition ON, verify that the ECT sensor parameter is at -40°C (-40°F).
^ If greater than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM.
Notice: Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw.
Important: The control module or the sensor may be damaged if the circuit is shorted to B+.
3. Test for less than 1 volt between the low reference circuit terminal 2 and ground.
^ If greater than the specified value, test the low reference circuit for a short to B+. If the circuit tests normal, replace the ECM.
4. Ignition OFF, remove the fuse that supplies B+ to circuit terminal C2-56 of the ECM.
5. Test for less than 5 ohms between the low reference circuit terminal 2 and ground.
^ If greater than the specified value, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
6. Install the fuse that supplies B+ to circuit terminal C2-56 of the ECM.
Important: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.
7. Ignition ON, connect a 3A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2. Verify the ECT sensor parameter is greater than 142°C (288°F).
^ If less than the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
8. If all circuits test normal, test or replace the ECT sensor.
Component Testing
1. Ignition OFF, disconnect the harness connector of the engine coolant temperature (ECT) sensor.
Important: A thermometer can be used to test the sensor off the vehicle.
2. Test the ECT sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the Temperature Versus Resistance - Engine Coolant Temperature Sensor table and verify that the resistance is within 5 percent of the specification.
^ If not within the specified range, replace the ECT sensor.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Engine Coolant Temperature Sensor Replacement
* Refer to Programming and Relearning Programming and Relearning