How To Test: P0117 OBD II Trouble Code (Ford 4.0L)

START HERE: Troubleshooting DTC P0117

The key to diagnosing and repairing trouble the P0117 ECT Sensor Circuit Low Voltage trouble code is remembering that your Ford's PCM thinks that the engine coolant temperature is at 250°F (121°C) or higher all of the time (even at start up when the engine is completely cold).

Fortunately, you and I can test the engine coolant temperature (ECT) sensor with a scan tool that's Live Data equipped.

Now, if you don't have a scan tool with Live Data capability and need to buy one, check out my recommendation here: Actron CP9580 Scan Tool Review.

Here's a brief description of the tests you'll be doing with the help of this tutorial:

1. Confirm the ECT sensor's temperature value.
   • Using the scan tool, we'll see if the ECT sensor is reporting a temp that's 250°F (121°C) or higher.
   • TEST 1: Checking The Engine Coolant Temperature Value.
2. Check that the ECT sensor connector's wiring is not shorted together.
   • This involves removing the hard plastic protector that's over the wires and inspecting the condition of the two ECT sensor wires.
   • We'll also do a wiggle test of the ECT sensor's 2 wires.
   • TEST 2: Checking The Condition Of The ECT Sensor's 2 Wires.
3. Unplugging the ECT sensor and verifying the PCM sees an extreme cold temperature.
   • In this test step, we'll unplug the ECT sensor from its connector and then, via the scan tool's Live Data mode, see if the PCM now reads -4 °F (-20 °C).
   • This test will help you to eliminate a bad PCM and/or a hidden electrical short somewhere in the wiring between the PCM and ECT sensor.
   • TEST 3: Disconnecting The ECT Sensor From Its Connector.
4. Testing the ECT sensor with the engine running.
   • In this test step, we'll see if the ECT sensor can report a rising coolant temperature as the engine idles and warms up.
   • TEST 4: Checking The Temperature With The Key On Engine Running.

TEST 1: Checking The Engine Coolant Temperature Value

Since the PCM sees the ECT sensor reporting an engine coolant temperature of 250°F (121°C) or higher as the reason for setting trouble code P0117 ECT Sensor Circuit Low Voltage, the first thing we'll do is use our scan tool to visually confirm this high temperature.

On our scan tool, the PID (Parameter Identification) that will let us see what temperature the PCM is seeing, is labeled as: COOLANT (see the photo in the image above).

If you don't have a scan tool and you need to buy one, check out my Actron CP9580 Scan Tool Review.

IMPORTANT: Start this test with a completely cold engine. Starting out with a cold engine will ensure the accuracy of your test results.

OK, this is what you need to do:

1. 1

   Connect your scan tool to your Ford and turn the key to the on position.
   
   NOTE: This test is done with the Key On Engine OFF (KOEO).

2. 2

   Go to its Live Data mode once the scan tool has powered up.
   
   Scroll down to the PID labeled COOLANT (°F)

3. 3

   The COOLANT PID should register a temperature that's ±10 °F of ambient temperature (if all is normal)

   1. So let's say that it's 50 °F outside, then the ECT sensor PID should register something between 40 to 60 °F.
4. 4

   You'll see one of three possible temperature results:

   1. -4°F (-20°C).
   2.        OR
   3. 250 to 300°F (-121 to -150°C).
   4.        OR
   5. The current outside coolant temperaute.

Let's interpret your test results:

CASE 1: Your scan tool shows a 250-300°F reading. This high temperature (when the engine is completely cold) confirms that there's a problem with the ECT sensor or its circuits.

Also, this test result tell us that the P0117 ECT Sensor Circuit Low Voltage Input code stored in the PCM's memory is reporting a real problem.

The most likely cause will be that the ECT sensor circuits (wires) are shorted together or the sensor has failed (internally).

The next step is to physically check the condition of the wires and do a simple wiggle test. Go to: TEST 2: Checking The Condition Of The ECT Sensor's 2 Wires.

CASE 2: Your scan tool shows a -4 °F (-20°C) reading. This confirms that you do have a problem with the engine coolant temperature (ECT) sensor or its circuits.

Seeing an extreme cold temperature of -4 °F (-20°C) indicates one of two things, either that the ECT sensor is bad or the ECT sensor connector's wires have an open-circuit problem (think unplugged sensor). You'll also see a diagnostic trouble code P0113 (ECT Sensor Circuit High Voltage) stored in the PCM's memory.

CASE 3: Your scan tool shows a temperature reading that's ±10 °F of ambient temperature. This tells you that at the moment the ECT sensor and its circuits are OK and more importantly, that the problem is intermittent.

But, since your scan tool retrieved a DTC P0117 the problem may just be hiding at the moment, I recommend doing the next three tests in this tutorial. Go to: TEST 2: Checking The Condition Of The ECT Sensor's 2 Wires.

If the ECT sensor passes TEST 2, continue on to TEST 3 and TEST 4 (or until one test is failed).