Error Code P0116: Engine Coolant Temperature (ECT) Sensor Circuit Range/Performance Basically, it refers to a PCM (powertrain control module, also known as ECM or electronic control module) reading irrationally or out-of-specifications voltage signals coming from the ECT.


The job of the ECT sensor is to measure the rise and fall of the ECT. It sends that critical data to the PCM, which allows the latter to provide better control for many components of Emission Control Systems, such as air fuel ratio, cooling fans, ignition spark timing, etc. It can be found in the coolant passage or in the block. It’s a two-wire sensor; with one wire providing 5V reference voltage for the PCM, and the other for ground.

The ECT sensor tracks the heat in the engine. The ECT sensor resistance will appear high when the coolant temperature is low and vice versa. The PCM monitors these readings and determines the coolant temperature that is able to provide good fuel management.

Basically, the ECT is a thermistor which changes its resistance based on the coolant’s temperature it’s connected to. The PCM expects slow change of resistance from the ECT signal circuit. If it senses that the change is too quick and inconsistent of the engine’s warm up, or if it determines there’s not enough changes in the ECT signal, then it will set the error code P0116.

When this error code is set, the cooling fans will be turned on, the engine coolant temperature gauge becomes defective and the AC compressor will be ordered Off Causes.

Error Code P0116 is actually a generic trouble code that applies to all vehicles made from 1996 up to the present. Of course, different makes and models have different specifications on their definition and troubleshooting.

Other error codes related to P0116 are P0115, P0117, P0118, P0119 P0125 and P0128.

Common Symptoms

Aside from the activation of the Check Engine light, some vehicles may not show noticeable abnormalities in drivability. In many cases however, common symptoms include:

  • Hard starting when cold, starts normal when warm
  • Poor fuel mileage
  • Rough idle
  • Engine hesitates until warm
  • Black smoke coming from tailpipe

Note that these symptoms may be lessened once the engine warms up.

Possible Causes

Common causes of this error code include:

  • Damaged ECT sensor
  • High resistance in sensor wiring
  • Damaged or faulty connectors
  • Damaged wiring harness or loose terminals at ECT or PCM
  • Engine overheat
  • Defective PCM (rare)

How to Check

Check the ECT reading using a scan tool. If the engine is cold, the IAT reading should match, or be similar to the outside temperature reading. If it doesn’t match with the outside temperature or the IAT, then check the freeze frame data from your scan tool (if applicable). This saved data will give you a good idea regarding your ECT reading when the fault occurred. There are two things you should consider:

  1. If the saved data shows that engine coolant reading was at its coldest (30˚ F), then that indicates the resistance of ECT was intermittently high. If so, search for an open in the ECT sensor ground and signal circuits then do whatever repairs are deemed necessary. If everything seems okay, warm up your engine while monitoring the ECT for intermittent jumps. If there are intermittent highs or lows, then you need to replace the ECT.
  2. If the saved data shows the reading of the engine coolant was at the warmest (250˚ F), then that means the ECT resistance was intermittently low. Again, look for a short to ground on the signal circuit and do whatever repairs are deemed necessary. If everything seems in good shape, warm up the engine while checking the ECT for intermittent jumping of high or low. If there is, then you need to replace the ECT.

How to Fix

The two most common fix for this trouble code is one; test and replace the thermostat, and two, testing and repairing any other related codes to ECT problems.

As with many error codes, the P0116 will set the PCM to failsafe mode, which may cause the engine to run erratically, with hesitation or to run rough until the engine is properly warmed up.