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Old 18th June 2017, 06:48 PM   #1
Pharmed
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Default IAT constant 40 degrees?

On my supercharged M3, I noticed a weird running issue today. The IAT is 40 degrees, constantly. I am 99% sure it was never like that as I had seen it at 20 etc. degrees a few days ago when playing around with Carly/Torque.

Funnily enough it stays at 40 degrees even with the sensor unplugged.

What could be going on?
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Old 19th June 2017, 07:21 AM   #2
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Duff sensor.
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Old 19th June 2017, 10:03 PM   #3
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What about when it is unplugged?
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Old 20th June 2017, 08:09 AM   #4
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Its obviously its default value when there is no reading from the sensor.
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Old 20th June 2017, 08:14 AM   #5
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Yep, it's the default reading.
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Old 20th June 2017, 09:03 AM   #6
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Yep, 40 degrees will give a big safety margin if the sensor fails so it's likely that's what has happened. You can buy the iat on its own for less than buying the whole MAF assembly.
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Old 20th June 2017, 09:09 AM   #7
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Quote:
Originally Posted by MWagon View Post
Yep, 40 degrees will give a big safety margin if the sensor fails so it's likely that's what has happened. You can buy the iat on its own for less than buying the whole MAF assembly.
Thanks. Any idea of the part number? Or where to buy if not bmw
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Old 20th June 2017, 10:15 AM   #8
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If it's supercharged, it won't have a MAF sensor.

More than likely you'll have a Bosch IAT - same spec as used in the original MAF. Part # 13621725323

Prior to ordering a new sensor, I would verify the wiring and connections check out ok.
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Old 20th June 2017, 11:28 AM   #9
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Quote:
Originally Posted by paulclaude View Post
If it's supercharged, it won't have a MAF sensor.

More than likely you'll have a Bosch IAT - same spec as used in the original MAF. Part # 13621725323

Prior to ordering a new sensor, I would verify the wiring and connections check out ok.
Thanks!
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Old 23rd June 2017, 09:10 PM   #10
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I changed the sensor and wiring all the way to the ecu. It looked like the ground wire had a break in it somewhere along the way.

Still shows a constant 40 degrees... No error codes... What is going on?!!
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Old 23rd June 2017, 09:54 PM   #11
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Maybe a mapping issue ?
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Old 24th June 2017, 04:06 AM   #12
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Quote:
Originally Posted by Pharmed View Post
I changed the sensor and wiring all the way to the ecu. It looked like the ground wire had a break in it somewhere along the way.

Still shows a constant 40 degrees... No error codes... What is going on?!!
Odd one for sure. I'm pretty sure it should go to 'null' value if the sensor is open circuit/disconnected. It must be seeing resistance from the circuit at some point for the 40deg value. With the DME and sensor disconnected, do you get resistance between the ground and signal on the connector? What pins are you wired into at the DME?
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Old 24th June 2017, 09:40 AM   #13
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Originally Posted by cossie1 View Post
Maybe a mapping issue ?
I thought that as well. Aaron Reeve mapped it and he has confirmed there is no reason it should be static 40.

Quote:
Originally Posted by paulclaude View Post
Odd one for sure. I'm pretty sure it should go to 'null' value if the sensor is open circuit/disconnected. It must be seeing resistance from the circuit at some point for the 40deg value. With the DME and sensor disconnected, do you get resistance between the ground and signal on the connector? What pins are you wired into at the DME?
I thought so as well. When you mean resistance between the ground and connector, what do you mean? simply measure the two pins on the connector? I would expect (no continuity) as it's brand new wiring but can check again.

I wired into the 52 pin block. pins 25 (brown earth) and 22 for power (yellow/blue wire)
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Old 24th June 2017, 10:22 AM   #14
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Quote:
Originally Posted by Pharmed View Post
I thought that as well. Aaron Reeve mapped it and he has confirmed there is no reason it should be static 40.

I thought so as well. When you mean resistance between the ground and connector, what do you mean? simply measure the two pins on the connector? I would expect (no continuity) as it's brand new wiring but can check again.

I wired into the 52 pin block. pins 25 (brown earth) and 22 for power (yellow/blue wire)
Yes, measure the two pins going to the DME (with the DME disconnected). If you have replaced the wiring right back to the DME connector however, then it's unlikely there is a wiring fault. The IAT sensor is simply varies resistance with temperature. If it is disconnected, you should have a fault code and some kind of Null value (pretty sure this isn't 40).

Have you verified the 40C value via INPA ? It's under analogue 1 values.
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Old 25th June 2017, 08:00 PM   #15
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Default IAT reading with sensor disconnected is -40C

On my standard E46 M3 from 2001, the ODB-II app I use shows a temperature of -40C when I disconnect the IAT sensor by unplugging the MAF sensor connector.
When connected it seems to read 7-10C above the outdoor ambient temperature when the car has been parked for 12 hours overnight, which seems strange.
I have also tested an old MAF sensor that I replaced because the air flow was reading wrong, but that shows about the same temperature offset too, even when not inserted in the inlet pipe.
Maybe I have a fault with the wiring or the controller, but others seem to be saying they have similar issues.
Ideas welcome.
Justin.
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Old 26th June 2017, 12:07 PM   #16
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Quote:
Originally Posted by paulclaude View Post
Yes, measure the two pins going to the DME (with the DME disconnected). If you have replaced the wiring right back to the DME connector however, then it's unlikely there is a wiring fault. The IAT sensor is simply varies resistance with temperature. If it is disconnected, you should have a fault code and some kind of Null value (pretty sure this isn't 40).

Have you verified the 40C value via INPA ? It's under analogue 1 values.
Yeah with the DME disconnected it shows no wiring fault. I haven't checked with INPA yet as all I have to hand is Carly and TorquePro

Quote:
Originally Posted by Happybug View Post
On my standard E46 M3 from 2001, the ODB-II app I use shows a temperature of -40C when I disconnect the IAT sensor by unplugging the MAF sensor connector.
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Which app are you using? I have 40 but not negative.
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