Technical Description of OBD-II Trouble Code
The circuit for the Engine Coolant Temperature Sensor is experiencing a high input.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to all vehicles manufactured in 1996 or later (Honda, Toyota, Volkswagen VW, Mazda, Dodge, Ford, BW, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The Engine Coolant Temperature (ECT) sensor is a thermistor that is screwed into a coolant passage in the cylinder head. The resistance of the sensor is high when the coolant temperature is low, and it decreases as the coolant temperature increases.
The Powertrain Control Module (PCM) supplies a 5-volt reference and a ground to the sensor. The PCM monitors the voltage drop to determine the coolant temperature. If the ECT reads a temperature below freezing after the engine has been running for more than a few minutes, the PCM identifies a circuit fault and sets this code. Alternatively, if the PCM determines that the sensor resistance is outside of the specified range, this code is set.
An example of an Engine Coolant Temperature ECT sensor
Potential Symptoms
Symptoms of a P0118 code could include:
Causes
A code P0118 may indicate that one or more of the following issues have occurred:
Possible Solutions
First, if you have access to a scan tool, check the reading of the coolant sensor. Does it display a logical number? If so, the problem is likely intermittent. Perform a “wiggle” test by moving the connector and harness to the sensor while observing the reading on the scan tool. Look for any drop-outs, as they would indicate a faulty connection. If the scan tool displays an illogical temperature, check the resistance of the temperature sensor. If it is outside of the specified range, replace it. If it is within the specifications, unplug the sensor and use a fused jumper wire to connect the two terminals of the connector. The temperature reading should now exceed 250 degrees F. If it does not, there is likely an issue with the ground circuit or voltage supply.
Check for a 5-volt reference voltage at the connector. Also, check for the presence of a ground at the connector. If you do not have a 5V reference or ground continuity, check for these at the PCM connector. If you have them at the PCM connector, then repair any open circuits or shorts between the PCM and the sensor. If you do not have them, remove the problematic wire from the PCM and then check for the proper voltage at the PCM pin. If it is now present, repair the short in the circuit. If it is not present after removing the wire and checking the pin, replace the PCM.
NOTE: Usually, P0118 indicates a faulty temperature sensor, but it does not rule out these other possibilities. If you are unsure how to diagnose a PCM, do not attempt to do so.
Other engine coolant engine light codes: P0115, P0116, P0117, P0118, P0119, P0125, P0128
