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  #13  
Old 04-05-2010, 03:40 PM
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Re: IAT ohm range?

The IAT will throw a code if it is not plugged in. I had this problem after swapping intake manifolds. In my case, I had a high voltage issue.

I highly doubt your thermostat code is related to the IAT.
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  #14  
Old 04-05-2010, 03:52 PM
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Re: IAT ohm range?

Yeah, I am going to check the obvious first, and be sure I seated it into the harness all the way and check to be sure the terminals inside that go to the thermistor (?) itself are not wet and/or touching (they're close together and it's possible they got tweaked). As far as I know, those two codes were not on until the last day or two (after I changed thermo).

As we were talking about farther up, my theory about why the P0128 came on was that the IAT was not positioned right, giving a false value. Seems the PCM looks at that, as well as coolant temp, etc. to determine if it's warming up properly (time mostly). I bet that made it sensitive enough to throw the light (for the thermostat) on. I highly doubt that just happened (thermo being bad) recently, as the rubber was tore up pretty good and the gauage was always on the lower side (now it's cloer to half).

So, keeping fingers crossed it's something simple like the connection. I dread taking it in the dealer and don't want them messing with anything!
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Old 04-05-2010, 07:20 PM
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Re: IAT ohm range?

John, that's BS that they don't sell the sensor separately. I've bought one before. It cost $27.75 back in Jan. 05. Which year and engine do you have? I found my notes on resistances on the box for the sensor. Depending on year/engine there might be slight differences in mounting, but I'll bet the resistances are about the same. This Mopar number is for an 05 Hemi Magnum: 1-04606487AB. The box has a date of 10/15/03, so there may even be a newer number. It also wouldn't surprise me that the 3.7 unit is essentially the same. The drawings in the shop manual all look the same, but they may not be accurate depictions of the true sensor.The resistance range I got was from about 2000-40000 ohms. When I did my temperature checks I got the following resistances:
32 degrees = 32k
40 degrees = 25.3k
80 degrees = 10.3k
120 degrees = 3.8k

By the way, where are you in So. Cal.? I grew up in beautiful downtown Burbank, lived in North Hollywood, Granada Hills, Northridge and Chatsworth, before moving to Idaho.

Oh, here's the info. on code, P0112

When Monitored:

With the ignition on.
Set Condition:

The (K21) Intake Air Temperature Sensor Signal circuit voltage is below 0.12 volt for 2.0 seconds.
Possible Causes
INTERMITTENT DTC
(K21) INTAKE AIR TEMPERATURE SENSOR SIGNAL CIRCUIT SHORTED TO GROUND
(K21) INTAKE AIR TEMPERATURE SENSOR SIGNAL CIRCUIT SHORTED TO (K960) INTAKE AIR
TEMPERATURE SENSOR GROUND
(K21) INTAKE AIR TEMPERATURE SENSOR SIGNAL CIRCUIT OPEN OR HIGH RESISTANCE
INTAKE AIR TEMPERATURE SENSOR
ENGINE CONTROL MODULE (ECM)
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Old 04-05-2010, 07:42 PM
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Re: IAT ohm range?

Here's the shop manual info. for DTC P0128:

Theory of Operation
The PCM predicts what the engine coolant temperature should be, based on the engine coolant temperature at
start-up, ambient temperature and how the vehicle is subsequently driven. The predicted engine coolant temperature
is compared to the Engine Coolant Temperature Sensor reading. The error between the two is calculated and
integrated with respect to time. When the Thermostat diagnostic runs, the integrated error is compared to a calibrated
threshold and pass/fail is determined. Separate pass and fail thresholds are used in order to improve accuracy
of the diagnostic.
When Monitored:

Engine running.
Set Condition:

This diagnostic will fail when the model temperature reaches 91 deg. C before the ECT. reaches 80 deg. C.
This monitor only runs after a cold start condition ECT, ACT, AMB are all within 10 deg. C. of one another. Two
Trip Fault. Three good trips to turn off the MIL.
Possible Causes
LOW COOLANT LEVEL
THERMOSTAT OPERATION
SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
TEMPERATURE SENSOR
SIGNAL CIRCUIT OPEN
SENSOR GROUND CIRCUIT OPEN
SIGNAL CIRCUIT SHORTED TO GROUND
SIGNAL CIRCUIT SHORTED TO THE (K900), (G931) SENSOR GROUND CIRCUIT
OTHER POSSIBLE CAUSES
PCM
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  #17  
Old 04-05-2010, 07:48 PM
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Re: IAT ohm range?

I'm in Downey and grew up mostly in La Habra area (northwest OC border), with some Yorba Linda thrown in, lol. Lived in WA state (wenatchee) for awhile and liked it up there, besides the lack of opportunity, so decided to stay here. Was supposed to cash out and move to CO a few years ago, but, well, you know how that goes...Some nice parts up in ID and had a couple friends move up there.

Thanks for the info again. You're an awesome IAT guru Yeah, mine is doing an opposite thing with the resistance, so I am thinking the IAT is gone now. I could've messed with it, who knows...must've been something I did cause it didn't come up until I started doing the intake thing. Oh well. I'll look for that part number and somebody has to sell it separately. We don't get to see the full napa catalog online, so who knows.

Well, took another reading...being my measurement is 27k ohms and it's about 65 degrees outside, I'd say I messed something up, somewhere. If I could find that sensor for a reasonable price, I'd like to get it and avoid the stealership.

I have a 2005 WK 4x4 with 5.7, btw
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  #18  
Old 04-07-2010, 10:14 AM
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Re: IAT ohm range?

Well, hopefully this will be my final update on the IAT fiasco. I finally disconnected the battery, to clear the PCM, and woohoo, no light yet (25 commute), so keeping fingers crossed!

I did a little research on the magnum IAT p/n and it does seem to be available. However, it looks a little different than ours, but I would say if the resistance level is the same, I don't see why it couldn't work. Hoping I don't have to worry about this anymore, but would be nice to have a source in case anybody has a problem with theirs. Funny how a $10 part (basing on 3.7) can cause such havoc, lol.

Thanks again for your help. I learned a lot here
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Old 04-07-2010, 08:41 PM
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Re: IAT ohm range?

Good show. Hope it stays fixed. If the plugs match, I think I'd spend the $10 and try the 3.7 one, just for giggles. If it works, you now have a spare, or a test unit, if it causes you any more trouble.
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Old 04-07-2010, 10:01 PM
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Re: IAT ohm range?

Yeah, I was tempted to buy one and compare. Maybe in the near future or something, when I get some funds...Be good to resolve this issue for future reference, too, as I hate paying inflated prices for things.
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Old 03-03-2011, 01:21 AM
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Re: IAT ohm range?

Check this...........The wiring harness runs behind the valve cover in between that and the fire wall, it will sometimes ride right on top of a bolt and wear a hole in the wiring harness and short a wire inside, this wiring harness contains the TPS, IAT, ECT and many others.
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Old 03-03-2011, 09:15 PM
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Re: IAT ohm range?

Guess it's time for a little inspection.
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Old 03-04-2011, 02:57 AM
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Re: IAT ohm range?

Lets us know if your wiring harness if the culprit...
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Old 03-04-2011, 04:54 PM
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Re: IAT ohm range?

Are you talking about the huge plastic covered harness in the back? If so, mine doesn't appear to be touching anything, but then again, I don't have a problem either. Still it doesn't hurt to look if it'll prevent a problem down the road.
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