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Old 11-30-2008, 11:48 AM   #1
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Default Strange IAT problem

I'm seeing a strange issue with my IAT reported in MT. It used to be almost perfectly in sync with the CLT when I turned the car on and now it says it's like 50 degrees warmer than it should be. How can I tell if the sensor is broken? Can I ohm it out? Is there a chart somewhere of the resistance at given temperatures? It's the standard GM open element sensor.
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Old 11-30-2008, 11:55 AM   #2
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Go to google and type GM AIT sensor and do an image search. It's out there. Yes, you can ohm test it. If you're MS1, I bet this is a easy-therm problem. But I have 0 experience with MS1.
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Old 11-30-2008, 12:11 PM   #3
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I'd be very surprised if it was software. I've had it running fine for awhile and have not changed the firmware image at all. I was looking at my longs and one day it just stopped reading properly. I will see if I can find the chart.
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Old 11-30-2008, 12:24 PM   #4
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I wondering when you put the values in easytherm, you didn't just make a 3 row ohm chart
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Old 11-30-2008, 12:42 PM   #5
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Yeah, but those values are through the whole system including the bias resistor and whatever else is in the circuit. I need the datasheet values so I can unplug the sensor and ohm it out to rule out/confirm the sensor is bad. If it's good, then that means either something went on the board or somehow data got overwritten in the firmware where it wasn't supposed to.

I think I found it:



Guess Autozone is good for something at least.
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Old 11-30-2008, 12:51 PM   #6
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You know. I've been noticing the same problem recently. Sometimes, not always, the IAT will be exactly 10 degrees higher than the CLT after the car has been sitting all night.
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Old 11-30-2008, 12:58 PM   #7
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Quote:
Originally Posted by johndoe View Post
You know. I've been noticing the same problem recently. Sometimes, not always, the IAT will be exactly 10 degrees higher than the CLT after the car has been sitting all night.
That sounds more like an easytherm problem. Keep a log of the temps when you turn the car on and see if it happens at certain temps. I had a similar problem and found out one of my bias resistors was a little lower than it was spec'ed to be. Changed the value in easytherm and it was almost dead on after.
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Old 11-30-2008, 01:23 PM   #8
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These are the before and after...

Before:


After:
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Old 11-30-2008, 03:07 PM   #9
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Quote:
Originally Posted by johndoe View Post
You know. I've been noticing the same problem recently. Sometimes, not always, the IAT will be exactly 10 degrees higher than the CLT after the car has been sitting all night.
Thats because the car cooled down over night with the air temp. Then in the morning the air starts to warm as soon as the sun comes up. Now whats gonna warm up quicker, the air or your coolant(which is sitting in a cast iron block that also cooled down to the lowest temp seen overnight)?
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