98 Explorer Check Engine Light on

[mwn245]

I have a 1998 Ford Explorer XLT with a 5.0 V8 in it and 123,000 miles.

The check engine light is on with a code of PO112, intake air temp sensor 1 circuit low.

I replaced the sensor twice and took it to my local garage and they could not figure out what it wrong with it.

If anyone can steer me in a direction I would greatly appreciate it.

Thanks,

Mike

 

[Mebob2001]

is it a 2 wire sensor or 3 wire? find out which wire is the power ground and signal, and test the circuit with a DOVM, make sure thats all good

 

[mwn245]

It is a 2 wire sensor. I have a digital multi meter. Do I just check it for voltage or is there series of tests I will have to do? I will not be able to work on it until Thursday or Friday but as soon as I can I will post the results.

Thanks for your quick response,

Mike

 

[Mebob2001]

It is a 2 wire sensor. I have a digital multi meter. Do I just check it for voltage or is there series of tests I will have to do? I will not be able to work on it until Thursday or Friday but as soon as I can I will post the results.

Thanks for your quick response,

Mike

Well its an NTC sensor if i do recall, so as resistance goes down as temp goes up, so hook up your DOVM on resistance scale and take a hair dryer and blow it over the sensor if it doesnt change u need a sensor, im sorry i can no find the spec for the resistance of the sensor its self, but i think its a gry wire that goes to the pcm and a Gry/red wire that is the feed to the sensor, if you have the stedy voltage on the grey/red wire and you check the wiring from the sensor to the pcm and nothings is abnormal and its only setting that oen code, i woudl say your safe to throw a sensor in it and be done with it, if it was my own trucks i woudl just look at the conttecor make sure its not melted look if it only set the one code, and look at the loom to see if its grounding out anywheres then throw a sensor on it and clear the code's but thats me

 

[mwn245]

Stumped

Well its an NTC sensor if i do recall, so as resistance goes down as temp goes up, so hook up your DOVM on resistance scale and take a hair dryer and blow it over the sensor if it doesnt change u need a sensor, im sorry i can no find the spec for the resistance of the sensor its self, but i think its a gry wire that goes to the pcm and a Gry/red wire that is the feed to the sensor, if you have the stedy voltage on the grey/red wire and you check the wiring from the sensor to the pcm and nothings is abnormal and its only setting that oen code, i woudl say your safe to throw a sensor in it and be done with it, if it was my own trucks i woudl just look at the conttecor make sure its not melted look if it only set the one code, and look at the loom to see if its grounding out anywheres then throw a sensor on it and clear the code's but thats me

I finally got around to checking this out.

I have the original sensor from Ford and an after market sensor. They both read the same. They start as open and when you heat them up they read continuity, around 15 to 18 ohms.

I also checked the voltage on the connector and the positive wire reads a steady 4.77 volts DC; and the other wire reads .13 volts DC.

All of the wiring from the pcm to the sensor looks good.

I am not sure what to do next.

Thanks for all of your help.

Mike

 

[1998Exp]

Seems like you have a short to ground in the sensor wire. I had the same problem, except to make things worse, it was intermittent. When I tested everything was fine; next day the code for the low signal shows up and the scanner reads something like 450 degree intake air temperature. Touch the harness and the problem goes away for a couple days, then returns. After puling my hair out for a long time found that the culprit was a sharp edge of the harness support bracket at the firewall. It poked through the insulation and was intermittently grounding the signal. Hope this helps some.

I finally got around to checking this out.

I have the original sensor from Ford and an after market sensor. They both read the same. They start as open and when you heat them up they read continuity, around 15 to 18 ohms.

I also checked the voltage on the connector and the positive wire reads a steady 4.77 volts DC; and the other wire reads .13 volts DC.

All of the wiring from the pcm to the sensor looks good.

I am not sure what to do next.

Thanks for all of your help.

Mike

 

[mwn245]

Seems like you have a short to ground in the sensor wire. I had the same problem, except to make things worse, it was intermittent. When I tested everything was fine; next day the code for the low signal shows up and the scanner reads something like 450 degree intake air temperature. Touch the harness and the problem goes away for a couple days, then returns. After puling my hair out for a long time found that the culprit was a sharp edge of the harness support bracket at the firewall. It poked through the insulation and was intermittently grounding the signal. Hope this helps some.

Last night I took a quick look at the wiring harness and on top of the intake in the back near the fire wall there is a bracket that was poking through the insulation of the wiring harness just as you said.

I took a piece of rubber roofing and tie wraped it in between the bracket and wiring harness and reset the light.

I drove it to work today, around 75 miles round trip, and the light didn't come on. I will know in the next few days if that was the problem.

Thanks for all of your help,

Mike

 

[mwn245]

Update

1998EXP

You hit the problem right on the head.

Once you described your problem it was very easy to find.

I wanted to make sure it was fixed before I reported, but the check engine light has not come in more than 1000 miles.

Thanks for the info.

Mike