START HERE: Troubleshooting DTC P0118

Remember, when the P0118 ECT Sensor Circuit High Voltage trouble code sets, your Ford's PCM thinks that the engine coolant temperature is at -4 to -46°F (-20 to -43°C), no matter how long the engine has been running.

With a scan tool that has Live Data capability, you and I can easily test the ECT sensor and troubleshoot the cause of the P0118 DTC.

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.
  2. Check that the ECT sensor connector's wiring is not shorted together.
  3. Jumper the ECT sensor connector's terminals with a jumper wire.
    • In this test step, we'll jumper the ECT sensor connector's terminals and then, via the scan tool's Live Data mode, see if the PCM now reads 250 to 300°F (121 to 150°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: Jumpering Together the ECT Sensor Circuits.
  4. Testing the ECT sensor with the engine running.

TEST 1: Checking The Engine Coolant Temperature Value

How To Test A P0118 Diagnostic Trouble Code (Ford 4.0L)

The very first thing we need to do, is see the coolant temperature the PCM is seeing.

If the engine coolant temp is at -4 to -46°F (-20 to -43°C), then we know the problem is currently present and that trouble code P0118 ECT Sensor Circuit High Voltage is reporting a true condition.

In Live Data mode, the scan tool's 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.

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 to -46°F (-20 to -43°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 -4 °F (-20°C) reading. This confirms that you do have a problem with the engine coolant temperature (ECT) sensor or its circuits and that the P0118 DTC is reporting a true condition.

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).

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 an extreme hot 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. You'll also see a diagnostic trouble code P0117 (ECT Sensor Circuit Low Voltage Input) stored in the PCM's memory

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

For further testing specifics, go to this tutorial: How To Test: P0117 OBD II Trouble Code (Ford 4.0L).

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 P0118 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).

Ford Vehicles:

  • Aerostar 4.0L
    • 1993, 1994, 1995, 1996, 1997
  • Explorer 4.0L
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003
  • Ranger 4.0L
    • 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003

Mercury Vehicles:

  • Mountaineer 4.0L
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003