Hey all. I have a 2003 Expedition 5.4 4x4 and am having issues with my IAT sensor. I'm getting code P0113 - Intake Air Temperature Circuit High Input.

Using my code reader I am getting a -40 degree Fahrenheit reading from the sensor during an Arizona Summer which is obviously incorrect. I tested the sensor itself with a hair dryer and multi-meter and when heat was applied the ohms dropped steadily so I am assuming the sensor is good.

I tried to verify voltage at the connector but am getting 0v at the connection. I stripped back the loom about 6 inches and found no breaks, stripped the wire and tested it there and am still getting 0v.

Anyone know where the power supply for this sensor is supposed to come from so I can verify voltage there, how many volts its supposed to be supplied with and what my next steps might be?

What is the negative effect on drive ability/engine wear if the IAT sensor doesn't work? Haven't noticed anything so far except the CIL being illuminated.

Hate to be a needy poster!

Thanks in advance!!

 

With the connector to the IAC disconnected, the gray/red wire should have 0 volts on it (ignition in RUN) and should show a direct short to ground (ignition off). With the ignition in RUN, the Gray wire should have +5V on it, this is the 5v reference voltage generated internal to the PCM.

If there is an open circuit anywhere in this circuit, the PCM will always register -40F, the limit of the sensor's calibration. Another test is to unplug the IAT connector and insert a jumper between the two pins of the harness connector, then retrun PCM quick test to see if you get the opposite code (P012). If you get that, the wiring and PCM is all good. If not, the sensor is bad.

Probably none. The PCM will realize that a sensor is faulty and will substitute a value for it that allows the PCM to adequately control fuel system and spark. The most you'd probably notice would be a slight reduction in fuel economy.

 

Thanks for the reply!

I've tried jumpering the connection with a paperclip and the -40 reading didn't change at all. Its supposed to read 200 something Fahrenheit when jumped right? I'll run the test again to verify that I get the different code.

So I'll look to see if I still have a good ground at the grey/red. I got 0v on both grey/red and grey with the truck running and with it off and ignition in run. Perhaps my PCM is at fault.

 

So I jumped the connector with a paper clip and nothing changed. No new codes and the temperature readout doesn't flicker.

I checked for a ground on the red/grey wire and there was a good ground there but i still have no voltage at the grey wire. I really don't want to tear the whole loom looking for breaks. Any other ideas?

 

Yes, there is still more pinoint diagnosis to be done.

Pull the connector off the TPS (it's easy to get to). Check for +5V on the brown/white wire with the ignition in RUN.

If the +5V is missing there, either there's a short circuit to ground on the +5Vref line or the +5V regulator in the PCM has failed. However, if that were the case, there would be other faults since other sensors also use that same reference voltage

If the +5V is present at the TPS connector, look for an open circuit in the wiring between IAT red/green wire and pin 19 of connector C175b on the PCM or an open circuit inside the PCM.

 

SO. I tested for 5v at the TPS and was rewarded with 5v.

I feel a bit silly but after testing for continuity i plugged the connector back into the pcm and started up the truck and the oil pressure reading was a 0 and I had the low oil lamp lit up. I realized that the connector might not be seated completely firmly.

I shut down the truck. Hit the connector with my fist to be sure it was seated well (and to vent frustration) and now all the electrical gremlins are gone. My IAT sensor issue is gone and I am reading oil pressure again.

Sometimes Its the weird things that get you.

Thanks for all your help!

 

That's aggravating as all hell.