Hey guys my 1990 f150 5.0l 4x4 auto has a code for the charge air temp sensor open circuit. I replaced the sensor and didn't do anything and I have ground at the black wire and a flickering ground at the white wire. Does anyone know what voltage in supposed to have or a wiring diagram?

 

The PCM supplies 5 volts as a "reference", we call it VREF for short. Most of the sensors like the ECT and your ACT are given 5 volts and return some back to the PCM depending on temperature, which affects resistance in the sensor. You should see 5V constant on one wire, the other wire goes back to the PCM as a signal return. My best guess is that there is an open circuit on the power wire after it separates from the wire harness. If the entire VREF harness had an issue then you would be getting a lot more codes. Trace that wire back to the splice and see if it got pinched or cut.

 

Ok thank you. But I have a white and black wire on mine. So the black wire that shows ground now should be 5 volts?

 

Disconnect the sensor while you test the wires. What you should do is turn the Key On, Engine Off, take your volt meter and check both wires for voltage. One should have 5V on it, the other will have no voltage. You have to establish that the sensor has power available to it.

 

O ok. I had the engine running when I checked for voltage. And I had ground at the black wire and a flickering ground at the white wire.

 

You have to check for VOLTAGE.

 

Sorry I wasn't clear, i was using my power probe so it checks for both at the same time.

 

use a volt meter and check for voltage. If you check resistance of the sensor, it shoud be around 37k ohms at 68 degrees F resistance decreases as temperature rises.

 

Ok il do that when I get off work, thank you!