Code P0118: Engine Coolant Temperature Sensor Circuit High Input

What Does the Code P0118 Mean?

As a generic Powertrain diagnostic trouble code, P0118 applies to all vehicles from 1996 to current makes and models. This error message relates to the engine coolant temperature sensor, which is a thermistor located in the cylinder head and screwed into the coolant passage. Essentially, this sensors job is to accurately relay the coolant’s temperature to the Powertrain control module by signaling resistance in conjunction with temperature shifts. Therefore, a high resistance reading of the engine coolant temperature sensor would indicate a low temperature. When the sensor consistently read a less than freezing temperature despite the engine running, the Powertrain control module sets the P0118 code. The code can also be triggered if the sensor is transmitting a resistance that is out of the normal operation of your vehicle.

Does P0118 Have Any Symptoms?

As with most error codes, one of the first symptoms you are likely to notice is the illumination of the malfunction indicator lamp or the check engine light. However, beyond this primary indicator, the other symptoms of this trouble code are pretty severe. For example, the fuel economy will be incredibly poor. Also, you might not even be able to start your vehicle. However, if you can start your car, you might run into other issues, like misfires, rough running, black smoke, etc. Therefore, while some diagnostic codes can be safely ignored, this is not one of them. The operation of your vehicle will probably be severely hindered until you get the underlying problem resolved.

What Are the Common Causes?

There are several possible causes for this error message, but don’t assume that there is only one culprit. The trouble code may be referencing several underlying issues. For example, you could have something as simple as a bad connection at the sensor or a bad ground circuit between the engine coolant temperature sensor and the Powertrain control module. Also, between the sensor and the Powertrain control module, you could have a voltage short. Or, you could simply have a temperature sensor that experienced an internal short. However, while not as likely as any of the other issues mentioned, you could have a bad Powertrain control module. Unfortunately, as all of these potential issues are electronic, you will have to rely on diagnostic and scan tools to find the primary problem.

What Are the Probable Solutions?

To begin your repair job, you will need a scan tool. You will use this tool to check the reading of the coolant sensor. What is the reading? Does it make sense? If it does, then you can safely assume the problem is intermittent. You can further diagnose the issue by wiggling the sensor harness and connector and watching the readings for drop-outs or illogical readings. Drop outs probably mean that the connection is bad. If the readings are illogical and out of spec for your vehicle, then you might need to replace the sensor. However, if readings are within range, then try using a fused jumper wire to max out the temperature readings. If the readings are not maxed out at 250 degrees Fahrenheit, then there is probably an issue with the voltage supply or ground circuit. Inspect for shorts or ground continuity along wires and connections, and make repairs as needed. The OBD-II scanner error code P0118 problem is often the result of a bad temperature sensor, but it is also possible that there are wiring and connection issues. Because of the potential dangers when driving, it is best to resolve your problem before taking your car on the road.