Technical Description of OBD-II Trouble Code
The input for this diagnostic trouble code (DTC) is a low signal from the Engine Coolant Temperature (ECT) Sensor Circuit.
What does that mean?
This generic powertrain code applies to all vehicles manufactured from 1996 onwards, including Honda, Toyota, Volkswagen VW, Mazda, Dodge, Ford, BW, and others. The specific repair steps may vary depending on the make and model of the vehicle.
The ECT sensor, also known as the Engine Coolant Temperature sensor, is a thermistor located in the engine block or another coolant passage. It changes its resistance based on the temperature of the coolant it comes into contact with. Typically, it is a two-wire sensor, with one wire receiving a 5-volt reference from the PCM (Powertrain Control Module) and the other wire serving as the ground supplied by the PCM.
As the coolant temperature changes, the resistance of the sensor also changes. When the engine is cold, the resistance is high, and when the engine is warm, the resistance is low. If the PCM detects a signal voltage lower than the normal operating range of the sensor, it will set the P0117 code.
An example of an Engine Coolant Temperature ECT sensor
Symptoms
Potential symptoms of this issue include:
Causes
Possible causes of the P0117 code are:
Possible Solutions
Since this code indicates an abnormally low signal to the PCM from the ECT, it means that the PCM detected an excessively “hot” condition in the engine coolant. This could be due to a faulty ECT sensor or wiring, but it could also be caused by an overheated engine. Therefore, if your engine was overheated, it is important to diagnose that issue first. If the engine was not overheated, here are the possible solutions:
Using a scan tool with KOEO (Key on engine off), check the ECT reading on the display. On a cold engine, the ECT reading should match the reading from the Intake Air Temperature (IAT) sensor. If it does not match, replace the ECT sensor.
1. If the ECT reading shows an excessively hot reading, such as more than 260 degrees Fahrenheit, unplug the ECT sensor. This should cause the ECT reading to drop to the extreme cold reading (around -30 degrees Fahrenheit or so). If the reading changes, replace the sensor because it is internally shorted. If the reading does not change, check for a short to ground on the signal circuit of the ECT wiring. It is possible that the two ECT wires are shorted to each other. Look for any chafing or melted wiring and repair as necessary.
a. If you cannot find any wiring problems and the ECT reading does not drop to the extreme coldest when unplugged, check for voltage coming out of the PCM on the signal wire’s pin at the PCM connector. If there is no voltage or the voltage is low, the PCM may be faulty. NOTE: On some models, it is possible for the 5 Volt reference signal to be temporarily shorted, which can happen if an engine sensor internally shorts the 5 Volt reference. Since the 5 Volt reference is a “shared” circuit on many models, this will cause it to be abnormally low. Usually, this will be accompanied by several other sensor codes. If you suspect this may be the case, unplug each sensor until the 5 Volt reference reappears. The last sensor unplugged is the offending sensor. Replace it and recheck the signal wire from the PCM connector.
2. If the scan tool ECT reading appears normal at this time, the problem may be intermittent. Use a “wiggle” test to manipulate the wiring harness and connectors while observing the ECT reading on the scan tool. Repair any loose or corroded wiring or connectors. If your scan tool has the Freeze frame data function, you can check the ECT reading when the failure occurred. If it shows the reading to be at the hottest extreme, replace the ECT sensor and see if the code reappears.
Other DTCs related to the ECT sensor and circuit: P0115, P0116, P0118, P0119, P0125, P0128
