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IAT sensor damage, work-around advice?
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ncmountainmadness Offline
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Post: #11
RE: IAT sensor damage, work-around advice?
Markvanh,

jameco is a good company, mouser electronics is another but rarely use them. if your serious about doing this, I wouldnt wast alot of time with radio shack, they just dont carry much anymore. They might online, but their prices are quite higher than the two Ive suggested. RS is the yuppies electronics supplier. Take the time and do your research to maximize the time you spend tinkering, then order online vs trying to hunt local.

OK....so atleast you have a baseline ohm reading of about 1100 ohm or 1.1k. But then again that is at the cold range. Thge only one I see that would come close at Jameco would be, B57164-K152-J
and it is rated at 1.5k....but at .44cents what would you have to lose

Have you checked it again since all the resetting?...youve never said or ive missed it... still find it quite hard to believe you fried it. Dont go prying it open until youve taken some ohm readings with it cold. since doing all the reset does the scanguage still show -40?


My advice is to do as much testing as possible using the ohm or continuity setting when testing such devices, and as stated with Batt off. I rarely if ever do any trouble shooting of such things with voltage readings. Matter a fact, except for test data Ive compiled on 02 and AFR sensors, while running I have as of yet to not figure things out useing just a simple multi meter.

attached is the method I have used with success on both the IAT and CTS on late model Toyota's, nissan should be quite similar. Most common variable resistor is 5kohm. The idea is to have the total circuit close to the original to start with then vary from ther. However using ohms law math, to keep the total circuit as close as possible to beginiing point I see yours should be in the 50k range, based on your iniital of 1.1k. 1 / 1/1100 + 1/50,000 = 1076 ohms. At 10k your circuit total would have been 991 ohms, pretty darn close. There is no way you damaged the thermistor with that. If at all, maybe in taking readings the wrong way with a digital VOM

Hope all of this continued to help. end of work day gotta go home, Check back in this weekend when working again. (slow computer at home).

MIke


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07-16-2008 02:20 PM
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markvanh Offline
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Post: #12
RE: IAT sensor diagnose & fix
Thank you Mike!!
Removed the sensor unit yest and was able to verify the 2 wires of the IAT sensor--the YR & Br, the first 2 terminals L to R. The tiny thermistor is fried. Tongue

There's a silver-ish splat mark on the casing, looks like it melted/popped and it measures open circuit. (I did check it again since resetting- w/ pot disconnected IAT reads 40 degF at scanguage, and I got same CEL code to reset). Yes, I think I must've fried it during VOM readings, should've been more careful and only tried to measure with ign off and disconnected. I stepped in it.

Those Jameco & Mouser thermistors look possible tho don't know if they'll match response %/ degC which from my crude measurement & calc might be about 1.52% per deg C. A local electronics store (not RS) before close had a $.50 1K NTC thermistor i bought though it doesn't have any specs; not installed yet.

Last night I searched Subaru owner forums and found a post saying, "Our MAF works by measuring the rate of cooling the incoming air does to the thermistor." Oops. This would mean the MAF is dependent on the IAT thermistor. In that case I should really match the orig thermistor very closely. I have noticed an occasional hesitation in my engine response since the tinkering, so I'm not sure what to think.

Stall. I doubt anyone at Subaru will give up the info on that thermistor so they can sell me a $350 sensor assy. Hmm
Well, I'm really learning here. Thanks again for the help. -Mark


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07 Subaru Forester 2.5X non-Turbo Auto Trans
(This post was last modified: 07-27-2008 01:30 PM by markvanh.)
07-26-2008 10:37 AM
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