TEST 4: Checking The Temperature With The Key On Engine Running

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

If you've reached this point, then all of the ECT sensor tests you've done so far (TEST 1, TEST 2 and TEST 3) show the ECT sensor behaving normally.

There's a good chance, that once the engine warms up, the sensor could start malfunctioning, so in this test you'll start the engine and let it warm up and make sure that the coolant temperature your scan tool is reporting actually rises.

IMPORTANT: You must start this last test with the engine completely cold, or your test results won't be accurate.

This is what you need to do:

  1. 1

    Check and take note of the coolant temperature your scan tool is displaying.

    The coolant temperature that your scan tool is showing, should be at or around ambient temperature.

    Now, touch the upper radiator hose with your hand. The hose will be cool to cold (ambient temperature).

    NOTE: The ECT sensor must be connected to its electrical connector for this test to work.

  2. 2

    Start the engine and let it warm up.

    As the engine runs, keep your eyes on the engine coolant's temperature (on your scan tool). The temperature displayed should rise.

    Every now and then, recheck the temperature of the upper radiator hose. It should still be cool to the touch.

  3. 3

    Once the coolant temperature has reached 190° F, check the temperature of the upper radiator hose by lightly touching it with your hand.

    The hose should now be hot to the touch since at 190° F the thermostat opens and lets hot coolant start to flow to the radiator. OK, let's interpret your test results below:

CASE 1: The coolant temperature displayed by your scan tool rose. This tells you that the engine coolant temperature (ECT) sensor is working correctly and that the ECT sensor problem, causing the ECT sensor code, is intermittent.

Here's why: In this test step, we've used the opening of the thermostat, which occurs at 190 to 195° F as a cross reference source for the temp sensor's accuracy.

Although this test is not 100% accurate, it is a good indicator of the ECT sensor's performance.

CASE 2: The coolant temperature displayed by your scan tool jumped between one negative number to a positive number (for example -30° F to 240° F) This confirms a malfunction with the engine coolant temperature (ECT) sensor. Replace the ECT sensor.

More Test Tutorials

If this tutorial was helpful/informative, you can find a complete list of tutorials here: Ford 4.0L Index Of Articles.

Here's a sample of the tutorials you'll find there:

Thank You For Your Donation

If this info saved the day, buy me a beer!

If This Info Saved the Day, Buy Me a Beer!

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