ECT Sensor Test (P0117, P0118) (GM 4.3L, 5.0L, 5.7)

TEST 2: The Wiggle Test

The wiggle test will help you to find out if the ECT sensor diagnostic trouble code is due to a false connection (at the connector) or a problem in the wiring.

You'll need a helper to wiggle the wires for you, as you keep your eyes glued on your scan tool. What you're looking for is to see if the wiggling will change the result you got in TEST 1.

To be a little more specific:

• If in TEST 1 you got a -40° F reading (which usually indicates an 'open-circuit' problem in one of the two ECT sensor's wires) then wiggling the sensor's wires could bring them back together and you would see the -40° F go back to a normal temperature reading.
• If in TEST 1 you got a 250° F reading (which usually indicates that the two ECT sensor's wires have shorted together) then wiggling the sensor's wires could get them to separate and you would see the 250° F go back to a normal temperature reading.
• If in TEST 1 you got a normal temp reading then wiggling the wires may cause the intermittent problem to present itself and you would see either a -40° F or 250° F on your scan tool.

OK, this is what you need to do:

1. 1

   With the key On (but with the engine Off), check the coolant temperature with your scan tool.

2. 2

   Have a helper gently wiggle the coolant sensor's connector and wires.
   
   Your job is to keep your eyes on the coolant temperature displayed on the scan tool.

3. 3

   What you're looking for is one of two things:
   
   The coolant temperature will stay the same (no fluctuations caused by the wiggling).
   
   Or, the temperature will all of a sudden change to a drastic temperature (either -40° F or 240° F).

Let's take a look at what your test results means:

CASE 1: The wiggle test DID NOT cause changes in the coolant temperature. This tells you that there are no wiring issues with engine coolant temperature (ECT) sensor.

Replace the ECT sensor if in TEST 1 you had reading of -40° F reading or a reading of A 250° F/

If in TEST 1 you got a reading of ±10° F of ambient temperature reading, go to: TEST 3: Checking The Temperature With The Key On Engine Running.

CASE 2: The wiggle DID create drastic changes in the coolant temperature (for example -30° F to 240° F). This confirms a malfunction with the engine coolant temperature sensor's connector or its two circuits.

The next step is to visually check that the two wires coming out of the connector are not fused together or at any point in the wiring harness.

Repairing the issue with the sensor's wire or connector will solve the diagnostic trouble codes (P0117, P0118).

TEST 3: Checking The Temperature With The Key On Engine Running

You're here because in TEST 1 and TEST 2, the coolant temperature sensor was reading a temperature that was within specification.

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.

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.

2. 2

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

3. 3

   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.

4. 4

   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:

Let's take a look at what your test results mean:

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

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 sensor. Replace the ECT sensor.

Related Articles

There are several 'how to' GM 4.3L, 5.0L, 5.7L tutorials. You can find them all in here: GM 4.3L, 5.0L, 5.7L Index Of Articles.

Here's a sample of articles:

• How To Test The Thermostat (GM 4.3L, 5.0L, 5.7L).
• Troubleshooting A Blown Head Gasket (GM 4.3L, 5.0L, 5.7L).
• How To Test The Ignition System (at: easyautodiagnostics.com).
• MAF Sensor Test (at easyautodiagnostics.com).
• EGR Valve Test (at easyautodiagnostics.com).

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