TEST 2: Checking The Condition Of The ECT Sensor's 2 Wires
In some cases, the PCM registers a P0117 ECT Sensor Circuit Low Voltage Input because the 2 ECT sensor's circuits (wires) are shorted together.
What usually happens is that the insulation of the wires falls off exposing the copper. Eventually these 2 wires touch and short together.
The example of the connector, in the photo in the image viewer, highlights this type of problem.
You don't have to check the entire length of the wiring between the PCM and ECT sensor connector, just the length nearest to the ECT sensor's connector (about 6 inches away from ECT sensor's connector).
OK, this is what you need to do:
Remove the hard plastic protector that's over the wires.
You need to expose the ECT sensor's wires starting from the connector to about 6 inches away (from the connector).
Check for dry-rot and/or insulation peeling off the 2 ECT sensor wires.
The most likely place you'll find this condition (dry-rot and/or insulation peeling off) is right near the ECT sensor's connector.
Have a helper wiggle the 2 ECT sensor wires while you observe the ECT sensor's PID labeled COOLANT (on your scan tool).
What you're looking for is to see if wiggling the wires has any effect on the temperature reported on your scan tool.
Let's interpret your test results:
CASE 1: The wires have dry-rot and/or insulation peeling off. This condition is the most likely cause of code P0117. You need to replace the engine coolant sensor's connector or repair/replace the affected wires.
CASE 2: Wiggling the 2 ECT sensor wires caused a change in the temperature reading. This test result tells you that the wires do have a problem.
You need to carefully inspect the connector and the 2 wires and replace and/or repair what is damaged or shorted.
To give you some more specifics: Gently wiggling the ECT sensor connector's 2 wires should have no effect on the ECT sensor reading displayed on the scan tool, unless the connector is bad or one of the wires has an ‘open’. Since wiggling the connector did have an effect, you now know that replacing the ECT sensor connector or repairing the problem in the wires will solve the ECT sensor and P0117 Code problem.
CASE 3: The wires DO NOT HAVE dry-rot and ARE NOT shorted together and wiggling the ECT sensor connector's wires DID NOT cause the temperature to change. This tells you that the ECT sensor connector and its wires are OK.
In most cases, this test result also tells you that the ECT sensor is the one that's malfunctioned and needs to be replaced. Before you do, I suggest one more test.
And this is to test to make sure that the PCM is not fried. This is a very simple test and it requires that you disconnect the ECT sensor from its connector and then checking, with your scan tool in Live Data mode, that the engine coolant temperature (ECT) sensor's PID is now reading -4 °F (-20°C).
For this test, go to: TEST 3: Disconnecting The ECT Sensor From Its Connector.
TEST 3: Disconnecting The ECT Sensor From Its Connector
In this test step, we're gonna' check that the PCM isn't fried and falsely accusing the ECT sensor as having failed.
Although the PCM going bad is very rare, it does happen and we need to eliminate this possibility.
Also, the ECT sensor's wiring may have an electrical short, between the PCM and ECT sensor, that could fool the PCM into thinking the ECT sensor is bad. We can test these two possibilities with a very simple test.
This test simply requires that we unplug the ECT sensor and then check the PCM's response. If the COOLANT PID now shows an extreme cold temperature of -4°F (-20°C), you now know that both the wiring and the PCM are OK.
OK, here's what you'll need to do:
Check the current COOLANT value on your scan tool's display.
Have a helper disconnect the ECT sensor from its connector (while you observe the ECT sensor's PID on your scan tool).
PID COOLANT should now read -4 °F (-20°C) for the engine coolant temperature (ECT) sensor reading.
- You'll also see DTC P0118.
Let's take a look at your test results:
CASE 1: The PID labeled COOLANT registered -4 °F (-20°C) - This test result tells you that the wiring between the PCM and ECT sensor connector is OK and that the PCM is not fried.
You have now confirmed 3 very important things:
- That the PCM is seeing an extreme cold temperature around 300 °F (TEST 1).
- That there are no shorts in the sensor's wiring or in its connector (TEST 2).
- That the PCM is OK (TEST 3).
Therefore, you can confidently conclude that the ECT sensor is bad and needs to be replaced.
CASE 2: The PID labeled COOLANT DID NOT register -4 °F (-20°C). Make sure that you're testing the correct wires, that your connections are OK, and repeat the test.
Then this tells you that you have a problem in the wiring between the ECT sensor and the PCM or that the PCM is fried (although a bad PCM is rare).
Although testing the wiring between the PCM and the ECT sensor is beyond the scope of this tutorial, you now have eliminated the ECT sensor as the source of the P0117.