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

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 said:

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.

Click to expand...

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.

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:

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