Temp gauge doesn't work with engine running (VIDEO) P0118 code, what gives?

[evolucion311]

Hey StangNet:

My 02 GT convertible is throwing a P0118 at me. KOEO the temp gauge reads correctly. When I crank the engine and it goes KOER the needle falls to the sub-zero range.

I have replaced both the PCM and ECT trying to fix this but it is to no avail.

Anyone seen anything like this?

Video here:

 

[trombonedemon]

A code P0118 may mean that one or more of the following has happened:

• A bad connection at the sensor
• An open in the ground circuit between the ECT sensor and the PCM
• A short in the voltage feed between the sensor and the PCM
• A bad PCM (less likely)
• A bad temperature sensor (shorted internally)

Possible Solutions

First, if you have access to a scan tool, check the reading of the coolant sensor. Does it read a logical number? If so, the problem is likely intermittent. Perform a "wiggle" test by wiggling the connector and harness to the sensor while

watching​

the reading on the scan tool. Watch for any drop-outs. Drop-outs would indicate a bad connection. If the scan tool reads an illogical temperature, check the resistance of the temperature sensor. If it is out of specs, replace it. If it is in specifications, unplug the sensor and, using a fused jumper wire, jumper the two terminals of the connector together. The temperature reading should now be maxed out to above 250 degrees F. If not, there is likely a problem with the ground circuit or voltage supply.
Check for 5 volts reference voltage at the connector. Also check for ground presence at the connector. If you do not have 5V ref. and/or ground continuity, check for these back at the PCM connector. If you have these at the PCM connector, then repair open or short between the PCM and the sensor. If you do not, remove the offending wire from the PCM and then check for proper voltage at the PCM pin. If it's present now, repair short on the circuit. If it isn't present after removing the wire and checking the pin, replace PCM
NOTE: Usually, P0118 is indicative of a bad temperature sensor, but doesn't rule out these other possibilities. If you're unsure of how to diagnose a PCM, do not attempt.

 

[evolucion311]

How does one test for a short to power?

I recently tore the heads off my engine and reinstalled them but when it comes to electrical diagnostics I am lost.

 

[trombonedemon]

How does one test for a short to power?

I recently tore the heads off my engine and reinstalled them but when it comes to electrical diagnostics I am lost.

Have you tried changing the temp sensor?

Get your self a volt-meter; shave some insulation off of the sides of the wire and find a ground. The ground off of the battery usually works well. At least test to see if the temp sensor is getting power, if it is, its likely the temp sensor. The good news is the code is temp sensor related.

How is that your temp sensor is malfunctioning but your fan is not running as soon as you start the car.

 

[evolucion311]

Yes, I did replace the temp sensor AKA the ECT. It was the first thing I tried.

I get a solid 4.6 volts when measuring the voltage at the sensor connection, that is between the two wires in the connector. I have also measured the resistance of the pins on the sensor itself and the result was about 5,000 ohms, which made sense since the car had been driven that morning and had a little time to cool off.

Here's the tricky part: I unplugged the sensor and went KOEO and the PCM still thought there was a signal from the ECT. With an unplugged sensor and going KEOR the temp gauge falls again.

 

[evolucion311]

I posted a video that is a bit clearer in describing the symptoms. As soon as the ECT temp needle falls the fan turns on.

 

[wmburns]

Disconnect the ECT sensor. Key on engine running. What happens if the pins of the ECT sensor connector are shorted (jumped) together? Look at the dash temperature gauge (hint, the gauge should go to hot). This is pinpoint test DA11 in the Ford service manual.

If it doesn't, likely then it will be necessary to test for an open or short to VPWR. This is pinpoint test DA12 and DA13.

Access the cluster diagnosis. This will cross check the function of the gauge to what the PCM "thinks" the temperature is.

http://www.allfordmustangs.com/forums/v6-tech/49159-diagnostic-mode.html

 

[evolucion311]

Jumpering the ECT connector does not change the temp gauge.

The car is going to the doctor tomorrow... I found a supposedly good electrical guy in Lawrenceville.

 

[evolucion311]

Well the car is fixed. The problem was a bad ECT sensor CONNECTOR at the wiring harness along with some stretched and corroded wiring to the connector.

For whatever reason my own diagnostics and wiggle test did not show a problem but then again I'm not a pro.... Just a former Electronic Warfare technician. Funny, I can test an maintain a giant radar array but can't find a simple car problem.

The code read was P0118 but during the troubleshooting I managed to set P0117 and P1117 as well.

 

[nyuk98gt]

evolucion311:

Glad to hear it is fixed. Just goes to show that things are easy when you know how, right? I bet there are not many things in a radar array that could get by you since you were doing that day in and day out. You did the usual stuff on the ECT connector (wiggle test) but the problem was a little more sneaky. Your electrical guy probably has seen this more than once so he was able to find it pretty quickly.

Now, go and enjoy the car. And thanks for posting the updates on the previous troubleshooting. That was a good read!

Last thing: thanks for your service.

Chris