Technical Description of OBD-II Trouble Code
The Circuit Range/Performance of the Engine Coolant Temperature (ECT) Sensor
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to all vehicles manufactured from 1996 onwards (Ford, Hyundai, Kia, Mazda, Mercedes-Benz, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The ECT (Engine coolant temperature) sensor is a thermistor that changes its resistance based on the temperature of the coolant it comes into contact with. The ECT sensor is usually located in the engine block or coolant passage and is typically a two-wire sensor. One wire supplies 5 volts from the PCM (Powertrain Control Module) to the ECT, while the other wire serves as the ground for the ECT.
As the coolant temperature changes, the resistance on the signal wire also changes accordingly. The PCM monitors this reading to determine the coolant temperature, which is crucial for proper engine fuel management. When the engine coolant is low, the sensor’s resistance is high, resulting in a high signal voltage (indicating low temperature) to the PCM. Conversely, when the coolant is warm, the sensor’s resistance is low, and the PCM detects a high temperature. The PCM expects to see gradual resistance changes on the ECT signal circuit. If it detects a sudden voltage change that is inconsistent with the engine warming up, it will trigger the P0116 code. Similarly, if it observes a lack of change in the ECT signal, this code may also be set.
Symptoms
If the problem is intermittent, there may not be any noticeable symptoms. However, the following symptoms may occur:
Causes
Possible causes of the P0116 code include:
An example of an Engine Coolant Temperature (ECT) sensor
Possible Solutions
If there are any other ECT sensor codes present, it is recommended to diagnose them first.
Using a scan tool, check the ECT reading. On a cold engine, it should match the Intake Air Temperature (IAT) reading or be equal to the ambient (outside) temperature reading. If it matches, check the freeze frame data on your scan tool (if available). The saved data should indicate the ECT reading at the time of the fault.
a) If the saved information indicates that the engine coolant reading was at the coldest extreme (around -30 deg. F), it is likely that the ECT resistance was intermittently high (unless you live in Anchorage!). Check for an open circuit in the ECT sensor ground and signal circuits and repair them if necessary. If they appear to be fine, warm up the engine while monitoring the ECT for any intermittent high or low jumps. If such jumps occur, replace the ECT.
b) If the saved information indicates that the engine coolant reading was at the warmest extreme (around 250+ deg.F), it is likely that the ECT resistance was intermittently low. Check for a short circuit to ground in the signal circuit and repair it if necessary. If it appears to be fine, warm up the engine while monitoring the ECT for any intermittent high or low jumps. If such jumps occur, replace the ECT.
Other ECT sensor and circuit related DTCs: P0115, P0117, P0118, P0119, P0125, P0128
