IAT sensor - Resistance
05-29-2011, 12:21 PM
#1
IAT sensor - Resistance
Yesterday, I checked the resistance of the IAT thermistor on the MAF of my car.
I pulled it out of my car, brought it inside where the room temperature was about 72°F and checked the resistance through it. It showed approximately 1.65 kΩ. Now looking at the service manual, the resistance at this temperature should be roughly between 2kΩ and 3kΩ. So it seems to be out of range... Shouldn't the ECU throw a code (P0112 or P0113) if the thermistor is out of range? And how is the car supposed to know the correct exterior temperature? Is there another temperature sensor somewhere else on the car to compare with the T° read by the thermistor on the MAF?
My car feels down on power as soon as the exterior temperature gets above 70°F, which is normal you are going to tell me, but about a year ago, I didn't feel the power decrease as much as I do now... so I think it may be related to the thermistor sending the wrong message to the ECU?
I pulled it out of my car, brought it inside where the room temperature was about 72°F and checked the resistance through it. It showed approximately 1.65 kΩ. Now looking at the service manual, the resistance at this temperature should be roughly between 2kΩ and 3kΩ. So it seems to be out of range... Shouldn't the ECU throw a code (P0112 or P0113) if the thermistor is out of range? And how is the car supposed to know the correct exterior temperature? Is there another temperature sensor somewhere else on the car to compare with the T° read by the thermistor on the MAF?
My car feels down on power as soon as the exterior temperature gets above 70°F, which is normal you are going to tell me, but about a year ago, I didn't feel the power decrease as much as I do now... so I think it may be related to the thermistor sending the wrong message to the ECU?
05-30-2011, 06:05 AM
#5
^^ sure man, I got it from there: http://www.newark.com/honeywell-s-c-...135-202FAG-J01
The serial number is 135-202FAG-J01.
Note that I currently don't have a CEL. But if you have a P0112 or P0113, it could either be a bad harness or a bad thermistor. If you want to be sure which one it is, you need to perform these two quick tests. You will just need a voltmeter.
- Check the voltage between pin 5 and gound. When you disconnect the harness form the MAF, pin 5 is located at the very left when you look at the harness pins with the plastic clip on the upper side of the harness. The voltage should read +/- 5V. Note that you have to put the ignition in the ON position (with engine off) to make this test. It will tell you whether or not your harness is damaged.
- To check the thermistor itself, pull the MAF out by removing the two HEX screw holding it to the MAF casing, take the MAF inside where you can control the air temperature. Set your voltmeter range so it can read up to 5kΩ and check the resistance through the thermistor. Refer to the graph on the OP to make sure you are in the acceptable range. If you are way off, you will probably need a new thermistor.
The serial number is 135-202FAG-J01.
Note that I currently don't have a CEL. But if you have a P0112 or P0113, it could either be a bad harness or a bad thermistor. If you want to be sure which one it is, you need to perform these two quick tests. You will just need a voltmeter.
- Check the voltage between pin 5 and gound. When you disconnect the harness form the MAF, pin 5 is located at the very left when you look at the harness pins with the plastic clip on the upper side of the harness. The voltage should read +/- 5V. Note that you have to put the ignition in the ON position (with engine off) to make this test. It will tell you whether or not your harness is damaged.
- To check the thermistor itself, pull the MAF out by removing the two HEX screw holding it to the MAF casing, take the MAF inside where you can control the air temperature. Set your voltmeter range so it can read up to 5kΩ and check the resistance through the thermistor. Refer to the graph on the OP to make sure you are in the acceptable range. If you are way off, you will probably need a new thermistor.
06-03-2011, 03:41 PM
#7
I replaced the thermistor today and it definitely feels like my car grew a pair of *****! 
Its 80 degrees outside today. Before I replaced it, the car felt very sluggish. It took forever for the rpm needle to go up at WOT. Now with the new thermistor it gets up there so much quicker
A fix that cost me $4
Its 80 degrees outside today. Before I replaced it, the car felt very sluggish. It took forever for the rpm needle to go up at WOT. Now with the new thermistor it gets up there so much quicker
A fix that cost me $4
06-04-2011, 11:18 AM
#10
Yes I did. I put them side by side and measured the resistance through them.
The old thermistor resistance was approximately 0.35kΩ less than the new thermistor. I did the test both inside with the air temperature around 70 degrees and outside with air temperature around 80 degrees.
The old thermistor resistance was approximately 0.35kΩ less than the new thermistor. I did the test both inside with the air temperature around 70 degrees and outside with air temperature around 80 degrees.
06-08-2011, 05:18 PM
#11
I could kiss you right now, Gizmo! You're truly a gentleman and a scholar. 
Now, let me riddle you this: Wouldn't the lower resistance BENEFIT the car's performance? It's showing that the higher the resistance, the lower the measured temperature. Wouldn't that mean that a higher resistance would trick the car into thinking the air temperature is colder than it really is and let it add less fuel to... Ohhhhhh... No, we don't want to trick the car, we want the car to know EXACTLY what temperature it is to get the exact mixture of fuel and air to yield the stoichiometric ratio! Right..?
Now, let me riddle you this: Wouldn't the lower resistance BENEFIT the car's performance? It's showing that the higher the resistance, the lower the measured temperature. Wouldn't that mean that a higher resistance would trick the car into thinking the air temperature is colder than it really is and let it add less fuel to... Ohhhhhh... No, we don't want to trick the car, we want the car to know EXACTLY what temperature it is to get the exact mixture of fuel and air to yield the stoichiometric ratio! Right..?
06-08-2011, 07:04 PM
#12
I could kiss you right now, Gizmo! You're truly a gentleman and a scholar.
Now, let me riddle you this: Wouldn't the lower resistance BENEFIT the car's performance? It's showing that the higher the resistance, the lower the measured temperature. Wouldn't that mean that a higher resistance would trick the car into thinking the air temperature is colder than it really is and let it add less fuel to... Ohhhhhh... No, we don't want to trick the car, we want the car to know EXACTLY what temperature it is to get the exact mixture of fuel and air to yield the stoichiometric ratio! Right..?
Now, let me riddle you this: Wouldn't the lower resistance BENEFIT the car's performance? It's showing that the higher the resistance, the lower the measured temperature. Wouldn't that mean that a higher resistance would trick the car into thinking the air temperature is colder than it really is and let it add less fuel to... Ohhhhhh... No, we don't want to trick the car, we want the car to know EXACTLY what temperature it is to get the exact mixture of fuel and air to yield the stoichiometric ratio! Right..?
I tried to read this and it just gave me a headache.
http://www.physicsforums.com/showthread.php?t=182862
06-09-2011, 06:11 AM
#13
Eirik,
Because the bad thermistor was reading a lower resistance than it should, it fooled the engine telling it that the air injected is hotter than it really is. Hotter air being less dense than cold air (less oxygen mass in a cubic feet of hot air than in a cubic foot of cold air), the engine thought there was less air mass. Consequently, the ECU was sending less gas and the mixture was lean… hence the loss of power. At least that’s my theory.
In any case, it fixed my power issue and brought back the smile on my face
Because the bad thermistor was reading a lower resistance than it should, it fooled the engine telling it that the air injected is hotter than it really is. Hotter air being less dense than cold air (less oxygen mass in a cubic feet of hot air than in a cubic foot of cold air), the engine thought there was less air mass. Consequently, the ECU was sending less gas and the mixture was lean… hence the loss of power. At least that’s my theory.
In any case, it fixed my power issue and brought back the smile on my face
Last edited by Gizm0; 06-09-2011 at 06:14 AM.
06-23-2011, 07:41 PM
#14
Junior Member
Join Date: Jun 2009
Posts: 21
I am getting 0113 codes and found this thread. I went and grabbed my multimeter and pulled the MAF out and tested the IAT. I was getting a reading of 0 kΩ no matter the range setting. Am I doing something incorrectly? Is my multimeter a pile of crap? Is the IAT shot? Am I an idiot? I noticed a black/grayish blemish on the sensor itself and made me believe it might be shot. I'm not very good with this kind of stuff... Might just pull the trigger on the sensor from http://www.newark.com/honeywell-s-c-...135-202FAG-J01 and hope for the best.
06-24-2011, 05:36 AM
#15
^^^^ Sounds like your thermistor is shot. I'd definitely buy a replacement one. For just a few bucks, it won't hurt your wallet to much if it doesn't fix the problem.
PS: Make sure you solder the new thermistor to the MAF, otherwise it might come loose and end up inside one of your cylinders...
PS: Make sure you solder the new thermistor to the MAF, otherwise it might come loose and end up inside one of your cylinders...
06-24-2011, 06:17 AM
#17
I ran without mine for a while, and finally decided to throw one in. Didn't feel a difference.
It's more of a reference and doesn't affect much if anything. Aside from that, our MAF's/IAT and stock ECU AFR is pretty bad, typically.
But considering it's less than 5$, it's worth a shot.
06-24-2011, 06:40 AM
#18
Alright, it's strange that you didn't feel a difference with or without the thermistor.
Then how would you explain that my car was feeling very sluggish before replacing the thermistor, and it happened every time after 10/15 min of driving, enough time for the engine bay to warm up. Then I replaced the thermistor and haven't felt any power loss since?
Then how would you explain that my car was feeling very sluggish before replacing the thermistor, and it happened every time after 10/15 min of driving, enough time for the engine bay to warm up. Then I replaced the thermistor and haven't felt any power loss since?
06-24-2011, 06:13 PM
#19
Every car is different. Maybe I felt a difference just didn't notice. I think it's best to install the IAT, it's cheap and easy and cheap insurance, and seems to give positive feedback.
06-24-2011, 09:02 PM
#20
Junior Member
Join Date: Jun 2009
Posts: 21
More than anything, I just want these codes to disappear. I went ahead and ordered a new thermistor hopefully this clears up the 0113 code, but I've still got to look more into the other code which I can't remember right now. Gas cap related is all I can remember and it's very common.
06-26-2011, 11:24 AM
#22
It's very easy. Just unplug the MAF, remove it from your car. With a pair of pliers, open the "jaws" that clamp the thermistor in place, remove the thermistor. Put the new thermistor in place, close the jaws, then solder it to make sure it doesn't come lose.
You can see pictures on this thread http://forums.maxima.org/5th-generat...-pictures.html
You can see pictures on this thread http://forums.maxima.org/5th-generat...-pictures.html
09-24-2011, 11:34 AM
#24
sorry for bumping an old thread, but I received my thermistor and installed it today.
Could anyone confirm that their replacement one ordered from the link above seemed to be... Bigger than the stock one?
Did I get the wrong one perhaps? Not too sure on how to read thermistors
Could anyone confirm that their replacement one ordered from the link above seemed to be... Bigger than the stock one?
Did I get the wrong one perhaps? Not too sure on how to read thermistors
09-24-2011, 01:55 PM
#26
did the p0113 turn off right away or did you reset ECU and it didn't come back?
I started the car a few times and drove it for 5 minutes (not even a mile and a half) ad checked the car and noticed the p0113 was still there.
I had checked the voltage on the harness and it looked good (about 4.9V).
As I said, the replacement I had definitely seems bigger than the old one.. I just reset the ECU and I guess now I'll have to wait. I don't really wanna pay for shipping for them to get it right.
Using this thermistor on a 2k1 MAF btw.
I started the car a few times and drove it for 5 minutes (not even a mile and a half) ad checked the car and noticed the p0113 was still there.
I had checked the voltage on the harness and it looked good (about 4.9V).
As I said, the replacement I had definitely seems bigger than the old one.. I just reset the ECU and I guess now I'll have to wait. I don't really wanna pay for shipping for them to get it right.
Using this thermistor on a 2k1 MAF btw.
Last edited by OnOiShNo0dl3Z; 09-24-2011 at 02:01 PM.
05-11-2012, 10:46 AM
#28
This is good information, should be a sticky. I ordered the IAT wire from https://www.mouser.com/Search/Produc...135-202FAG-J01 because you don't have to create an account. I will post my results of the test along with an impression once I get the new IAT wire installed. Test procedure post http://forums.maxima.org/8064503-post5.html
I am using the 2000-2001 maxima MAF with the IAT wire from my suspected bad 2002 MAF. No codes but the engine still feels real sluggish.
-Edit, I tested 4.9 volts from the MAF harness pin 5 with igntion ON. Taking the MAF inside, I get 1.9 kOhms which as far as I can tell from the graph is good.
I am using the 2000-2001 maxima MAF with the IAT wire from my suspected bad 2002 MAF. No codes but the engine still feels real sluggish.
-Edit, I tested 4.9 volts from the MAF harness pin 5 with igntion ON. Taking the MAF inside, I get 1.9 kOhms which as far as I can tell from the graph is good.
Last edited by RR5; 05-12-2012 at 01:59 PM.
10-01-2012, 10:47 PM
#29
Junior Member
Join Date: Jul 2009
Posts: 31
Reply
The IAT can definitely cause a loss of power, based on the temperature the ECU sees coming into the engine, the computer has to decide how to advance the timing, on colder mornings or cold temperatures, the computer advances the timing further than usual, so if it has no reading of the IAT, it will leave the advancement back at 14° before top dead center which would result in a noticeable loss of power
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