Diagnostic Trouble Code P0118

P0118 “Engine Coolant Temperature Sensor Circuit High”


What is code P0118?

Code P0118 stands for “Engine Coolant Temperature Sensor Circuit High”. This diagnostic trouble code can show up for a number of reasons that have to do with the engine coolant temperature sensor on your engine. Therefore, it is important to have a qualified technician diagnose the specific problem that caused the code to be stored in your vehicle’s computer.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.

What does code P0118 mean?

A technician understands that code P0118 on a diagnostic scan of your vehicle means that there is something going on with the engine coolant temperature (ECT) sensor on your engine. Code P0118 is the generic code for when the data that comes from the sensor is above its normal voltage range.

Your engine is designed to operate within a certain temperature range for optimum performance. If it runs too cool, your engine will have poor fuel economy and increased emissions due to the fuel failing to atomize properly and the oil becoming too thick or viscous to circulate as it should. On the other hand, if the engine runs too hot, spark knock, pinging, and overheating can cause internal engine damage.

Since operating temperature is so critical to the performance and health of an engine, vehicle makers install a sensor that monitors the temperature of the engine coolant (“antifreeze”) that circulates through the engine block. This is the ECT sensor. When your engine is running, the ECT sensor continuously relays coolant temperature data to the ECM (Engine Control Module), the computer that monitors and controls engine function. The data is used to adjust how much fuel is injected into the combustion chambers, how wide the thermostat should be opened, when the spark plugs should be fired, and other operations.

If the ECM detects that the voltage level coming from the ECT sensor is above its normal range, meaning the engine coolant temperature is too low, it will store a code P0118 and turn on the check engine light.


What causes code P0118?

A number of causes can trigger a code P0118. That is why an accurate diagnosis is essential. Causes of this code include:

Most likely

Other possibilities

  • Damaged, dirty, or deteriorated wiring to the ECT sensor
  • Corrosion on the sensor connector or ECM connector
  • Bad ECM


What symptoms are associated with this code?

Common signs associated with a code P0118 include the following:

  • The check engine light is on or flashing
  • Erratic readings on the engine temperature gauge
  • Reduced fuel economy
  • Difficulty starting the engine, especially in cold conditions
  • Engine runs roughly or hesitates while warming up (but runs normally when warmed)
  • Failed emissions test


How does a technician diagnose code P0118?

If a diagnostic scan of your vehicle indicates a code P0118, a technician will perform tests to pinpoint the problem. These tests include checking for any related trouble codes. The technician will also use the scan tool to view live data from the ECT sensor to determine whether or not it is consistent. If the temperature is unusually cool on a warm engine, the technician might also check the coolant level or the thermostat. The wiring from the ECM to the ECT sensor will be inspected for cracks, corrosion, contamination, or bent pins on the connectors. The technician might also perform tests on the ECT sensor itself with a multimeter and verify that adequate voltage is reaching the sensor when it is in operation.


How serious is this code?

In some cases, you might not notice any symptoms when a code P0118 is present. Driving your vehicle in the short term with a code P0118 might result in reduced fuel economy, increased emissions, and a failed emission test. But it is not uncommon for the ECM to place your engine in failsafe mode, substituting a predetermined set of data for the live sensor data. When this happens, your engine can run rough until it warms up. Excessive fuel consumption and carbon buildup inside the cylinders is also possible, leading to problems down the road if ignored. For these reasons, you should have this problem addressed within a reasonable amount of time, usually a week or so.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.


Related Diagnostic Trouble Codes

P0115 Engine Coolant Temperature Sensor Circuit Malfunction

P0116 Engine Coolant Temperature Sensor 1 Circuit Range/Performance

P0117 Engine Coolant Temperature Sensor Circuit Low


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