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Peter_D Sun 5th February 2017 05:46 PM

Intake air temperature sensor code 112
I am new to the Subaru World - my daughter has a much loved 2001 Bug Eye Impreza that, up to this point, has been an absolute delight. However, I will be appreciative of any assistance with our current problem. The Check Engine Light illuminates occasionally at which point performance deteriorates markedly. The code thrown (live and stored) is 112 - INTAKE AIR TEMPERATURE CIRCUIT MALFUNCTION. We have replaced the IAT Sensor, the connector and conducted a pin out check back to the EMS ECU. Additionally, there is a new TPS that has been set to specification.

I have re-set the ECU a couple of times BUT the problem quickly returns. It is totally intermittent with no pattern as to hot, cold traffic or highway.

Any ideas will be greatly appreciated as I am running out of ideas. The Impreza has 160K kilometres, is driven very gently and has been maintained almost fanatically.

Thanks in advance.

TOONGA Tue 7th February 2017 08:42 AM

Does the car run a standard air cleaner assembly or an aftermarket job?

Have you checked for air leaks in the intake between the air cleaner and IAT Sensor and then from the IAT Sensor to the throttle body?


El_Freddo Wed 8th February 2017 06:49 PM

Welcome to the forum Peter D.

Are there any other codes logged as well?

Was the replacement sensor a new genuine unit/aftermarket unit or a second hand one?

This info maybe helpful in solving your issue. Your daughter's is a baby in the km department and has plenty more left in it before you move it on!

Hopefully we'll/you'll sort out a solution from info shared.



Suby Spanner Fri 10th February 2017 10:49 PM

If that fault code is as you say "circuit malfunction" it should be a purely electrical fault.

So, has the car had a prang recently, or any other work that would see the wiring messed with? It's possibly a dodgy earth somewhere. Or even as silly as recently jump started. Or a leaky windscreen letting the ECU get wet.....

What I'd be doing is grabbing a workshop manual, and work through the diagnosis: Which will be:
Read the sensor reading in the ECU and checking the wiring. I'd be finding where the sensor get's it's power from, confirming that's good, then confirming the earths good, then strap a multimeter across those two points and play with the wiring.

[EDIT] Ah, so you've tested the circuit to the ECU, did you check for short to earth and power?

Intake air temp sensor is a stand alone circuit (in most case, I would think a Jap car it would be certainly).... Although! Some AFM's have and IAT in them also, it's not a AFM fault is it?

Where as if it's just a air temp parameter fault (ie. not circuit malfunction), it could be a coolant temp sensor isn't right, but the ECU interprets that the IAT is wrong etc..

I hate modern faults, their codes and misleading names: Determing what the fault is, and what the symptom is can often be a bigger battle than the repair. :(

For example: I recently got caught on an audi, the A/c wouldn't work, the fault code was system pressure too high, but the fans weren't working... So were the fans not cooling the condensor causing the high pressure (which it will) or was the pressure sensor wrong (very very common) and not triggering the fans.... Both the fan control and the sensor out put are duty cycle, so you can't really test either signal without the correct expensive equipment, even then you'd need to know what those signals for that model need to look like....... Lot's of thinking... measuring temperatures with laser thermometers etc... and enventually I was nearly 100% sure it was the fans... but then, was it the fans themselves, or the speed control module, or the wirings.... yada, yada, yada.... eventually I was almost convinced it was the fan speed control module (which was hard wired in the loom, yes very expensive).... swapped it out... Bingo, problem solved, phew.... There was always a chance it was the pressure sensor, that's just how the fault detection systems work, their bloody dumb.

Peter_D Sun 12th February 2017 01:17 PM

Thanks to Suby Spanner, Toonga and El-Freddo for your replies. Just a couple of update points.
  • This is the combined type of IAT & MAP Sensor. It is positioned in the Intake Manifold after the Throttle Body.
  • There has been no water contamination in any part of the cabin. The EMS ECU is mounted solidly and the three (3) connectors are clean and sound. I believe the EMS ECU had never been disturbed until I recently removed it.
  • Being obsessive compulsive (and having the car for a year while my daughter was overseas), I completely checked and cleaned every earth. Anyone who has had an E Series Ford will have this obsession.
  • The replacement IAT / MAP is an original Bosch, same part number as the sensor I removed.
  • As suggested, I have tested the circuits from the sensor to the ECU. The voltage coming from the sensor is exactly the same as coming into the ECU (green wire). I also tested the linearity of this voltage (voltage in accordance with rpm's) and this was a bit irregular / erratic, however output voltages tallied with input voltages.
  • It had previously thrown an additional Code 1112, "Atmospheric pressure sensor range/performance problem" as well as 0112 - Same Sensor throwing a different fault. Now it is just throwing 0112.
  • As Suby Spanner correctly notes, code interpretation is an underlying issue. I can concur with the often 'psychotic' nature of some codes in relation to what is really going on. This is why I replaced the TPS as this has proved to be a relatively common problem (in many makes) that is often not giving a TPS error code. This potentially unnecessary replacement was the elimination of a possible (potential) problem.
  • A thorough vacuum test was conducted. 21.5"/hg, @ idle, solid needle. Text Book. I also checked all intake fasteners and listened for leaks with a stethoscope; intake all 'tip top'.All harness connectors checked and cleaned.

The only thought now is that the second sensor is defective. I have installed the old (failing) sensor and there is a different pattern to the fault code i.e. it is far less frequent. As such I have ordered a (further) replacement and now await delivery.

Will keep you updated on this one. This is a lovely little car and I intend to persevere until the fault is corrected. Thanks again for the input and support.

TOONGA Mon 13th February 2017 10:54 AM

Does the car run a factory standard air cleaner assembly or an aftermarket job?


Peter_D Mon 13th February 2017 07:56 PM


Originally Posted by TOONGA (Post 244523)
Does the car run a factory standard air cleaner assembly or an aftermarket job?


Absolutely everything is 'bog standard' including the Air Intake. That is, of course, except for the 'bling'. The only coincident event was that not long after I had cleaned the old MAP / IAT (it was cruddy) the first code began to appear intermittently.

Interestingly, the old sensor is now installed and over the last few days the frequency of fault codes is less. I am trending towards the view that it could indeed be a defective second sensor.

TOONGA Tue 14th February 2017 09:24 AM


Originally Posted by Peter_D (Post 244524)
Absolutely everything...'bog standard' including That is, of course, except for the 'bling'...

'bling' ? what is the bling? one of the recommendations for fixing this code is replacing the dirty air filter ... I can't find the page again sorry ...

How are you clearing the stored codes?


Peter_D Tue 14th February 2017 08:09 PM


Originally Posted by TOONGA (Post 244525)
'bling' ? what is the bling? one of the recommendations for fixing this code is replacing the dirty air filter ... I can't find the page again sorry ...

How are you clearing the stored codes?


"Bling" = wheel spats, sill moulds, cargo net etc. Nothing affecting the powertrain.

Air filter is brand new - changed last month. Standard Ryco paper element and exactly the same as we have been using before the code problems.

Code Clearing is as per manual - ignition etc protocols / procedure with Black and Green Connectors joined. Codes clear (flash confirmation) but return.

New Sensor due this week .........

TOONGA Thu 16th February 2017 10:06 AM

Believe it or not invest in something like this

Torque pro ( I have it for Android pm me your email for a copy)

And a an android phone or tablet with blue tooth

This Obd2 dongle works with my wife's 2010 TD forester and not only does it clear codes when calibrated to the vehicle (very easy) it has the engine parameters as well


boring video for torque pro

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