P0117 - Engine Coolant Temperature Sensor Circuit Low
Theory of Operation
The Engine Coolant Temperature Sensor (ECT) is located near the thermostat housing and is used to measure the engine coolant temperature. The Engine Coolant Temperature Sensor receives 5-Volts and a sensor ground from the PCM. The PCM monitors the change in voltage to determine the coolant temperature. There are two parts to this fault code, a key on check and a rationality check. After an eight hour cold soak, at key on the readings for the Inlet Air Temperature, Intake Air Temperature and Engine Coolant Temperature Sensors are all compared. If the temperatures differ more than a calibrated amount, then the appropriate sensor fault code would be recorded. The key on monitor is disabled for ambient temperatures below 20°F. This monitor looks for all the sensors to be grouped on one temperature or, in the case that the monitor fails, two sensors grouped at one temperature and one outlier. In the case that all three sensor values are distributed over a range of temperatures this diagnostic will not run. A block heater is one possible cause of such a distribution. The PCM rationality check looks at the temperature reading from the sensor over time and ensures that it changes with engine running. If the sensor reading does not change over a calibrated time limit, the fault will be recorded. Both the key-on and rationality portions of this monitor require that the diagnostic fails in two consecutive drive cycles before the MIL lamp is lit. The ETC lamp will also be illuminated. During this time the PCM uses a default value for the Coolant Temperature Sensor. The PCM turns off the MIL lamp when the
diagnostic runs and passes in four consecutive drive cycles.
When Monitored and Set Conditions
When Monitored: This diagnostic runs continuously when the following conditions are met:
• With the ignition on.
• Battery voltage greater than 10.4 Volts.
Set Conditions:
• The Powertrain Control Module (PCM) detects the Engine Coolant Temperature (ECT) Sensor Signal circuit is below a calibrated threshold.
Default Actions:
• The MIL is illuminated.
Possible Causes
ECT SENSOR SIGNAL CIRCUIT SHORTED TO GROUND
ECT SENSOR SIGNAL CIRCUIT SHORTED TO ENGINE COOLANT TEMPERATURE SENSOR RETURN
CIRCUIT
ENGINE COOLANT TEMPERATURE (ECT) SENSOR
POWERTRAIN CONTROL MODULE (PCM)
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 28 - DTCBased Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
Diagnostic Test
1. ACTIVE DTC
1. Turn the ignition on.
2. With the scan tool, record all Freeze frame data.
3. With the scan tool, erase DTCs.
4. Turn the ignition off for 75 seconds.
5. Turn the ignition on.
6. With the scan tool, read DTCs.
Did the DTC reset?
Yes
• Go To 2
No
• Perform the INTERMITTENT CONDITION diagnostic procedure. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
2. CHECK THE COOLANT TEMPERATURE SENSOR
1. Turn the ignition off.
2. Disconnect the Engine Coolant Temperature Sensor (ECT) harness connector.
NOTE: Check connectors - Clean/repair as necessary.
3. Measure the resistance between ground and one of the terminals of the ECT Sensor.
Is the resistance below 10k Ohms?
Yes
• Replace the Coolant Temperature Sensor in accordance with the Service Information..(Refer to 07 -
Cooling/Engine/SENSOR, Coolant Temperature/Removal)
• Perform the POWERTRAIN VERIFICATION TEST - 6.7L. (Refer to 28 - DTC-Based
Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
No
• Go To 3
3. CHECK THE (K2) ENGINE COOLANT TEMPERATURE SENSOR SIGNAL CIRCUIT FOR A SHORT TO GROUND
1. Disconnect the PCM C1 harness connector.
NOTE: Check connectors - Clean/repair as necessary.
2. Measure the resistance between ground and the (K2) ECT Sensor Signal circuit at the ECT Sensor harness connector.
Is the resistance below 10k Ohms?
Yes
• Repair the (K2) ECT Sensor Signal circuit for a short to ground.
• Perform the POWERTRAIN VERIFICATION TEST - 6.7L. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
No
• Go To 4
4. CHECK FOR THE (K2) ENGINE COOLANT TEMPERATURE SENSOR SIGNAL CIRCUIT SHORTED TO THE (K914) ENGINE COOLANT TEMPERATURE SENSOR RETURN CIRCUIT
1. Measure the resistance between the (K2) ECT Sensor Signal circuit and the (K914) Sensor Ground circuit at the Coolant Temperature Sensor harness connector.
Is the resistance below 10k Ohms?
Yes
• Repair the short between the (K2) ECT Sensor Signal circuit and the (K914) Sensor Ground circuit.
• Perform POWERTRAIN VERIFICATION TEST - 6.7L. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
No
• Go To 5
5. POWERTRAIN CONTROL MODULE
1. Disconnect all PCM harness connectors.
2. Disconnect all related in-line harness connections (if equipped).
3. Disconnect the related component harness connectors.
4. Inspect harness connectors, component connectors, and all male and female terminals for the following conditions:
• Proper connector installation.
• Damaged connector locks.
• Corrosion.
• Other signs of water intrusion.
• Weather seal damage (if equipped).
• Bent terminals.
• Overheating due to a poor connection (terminal may be discolored due to excessive current draw).
• Terminals that have been pushed back into the connector cavity.
• Perform a terminal drag test on each connector terminal to verify proper terminal tension.
Repair any conditions that are found.
5. Reconnect all PCM harness connectors. Be certain that all harness connectors are fully seated and the connector locks are fully engaged.
6. Reconnect all in-line harness connectors (if equipped). Be certain that all connectors are fully seated and the connector locks are fully engaged.
7. Reconnect all related component harness connectors. Be certain that all connectors are fully seated and the connector locks are fully engaged.
8. With the scan tool, erase DTCs.
9. Using the recorded Freeze Frame and Environmental Data, along with the When Monitored and Set Conditions above, operate the vehicle in the conditions that set the DTC.
10. With the scan tool, read PCM DTCs.
Did the DTC return?
Yes
• Replace the Powertrain Control Module (PCM) in accordance with the Service Information. (Refer to 08 -
Electrical/8E - Electronic Control Modules/MODULE, Powertrain Control/Removal) .
• Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain
Control (PCM) - Standard Procedure).
No
• Test complete.
• Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain
Control (PCM) - Standard Procedure).