Mechanics -- A Little Help Please?

[Ben]

I took my 2000 Trooper into the shop Friday to have the timing belt replaced and the auto transmission serviced. After I got it back and about a mile before home, the check engine light came on. I plugged in my code reader and got a "P0113 - IAT sensor 1 circuit high input". IAT = Intake Air Temperature.

I wanted to verify if while replacing the timing belt they could have accidentally knocked around the sensor or tweaked the wires or something. In other words, is it likely this could have resulted from the work they were doing? If so, I figure I can get the shop to fix it for free. If not,  I would rather give it a shot myself. From a quick Google search, the sensor runs around $20 and is semi-plug and play, while having the shop do it would probably run around $100.

[K Frame]

Just replace it. It's possible that they knocked it about, it's also possible that, at going on 10 years old it just decided it was time to quit.

"Proving" that they caused the issue is virtually impossible.

[White Horseradish]

Not sure how that particular sensor functions, but the first thing I'd do is to see if the plug is loose or even plugged in at all. Forgetting to reconnect something is fairly common.

[drewtam]

I am not an E&E expert, but here is my $0.02

Generally air temperature sensors are a probe (metal stick, forms a very long compact U shape) with two wires attached. The probe changes electrical conductivity with temperature, a computer measures that resistance and calculates temperature from a built in calibration chart in the software. Sometimes, it might be designed with a very small electronic box between the sensor and the ECM to translate the electrical resistance into a SAE standard computer signal. Often, that function will be built into the ECM itself.

FMEA:
http://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis

There are no moving parts or significant current. The air intake is relatively clean and low impact/vibration. So the sensor should be extremely reliable. Possible failures modes: broken wire, bad/broken connectors, broken probe tip, damaged electronic "translator" (if equiped).
The effects of the first three should be sensor reads too high temp/resistance. The fourth one might appear as sensor reads too low temp, if the board shorts out.


"High Input" sounds like the electrical resistance is too high, probably infinite - i.e. open circuit.
Therefore, I would look for loose wiring or a broken sensor by mishandling.

[BReilley]

stuff

I am with drew.  Simple parts like that rarely fail, and diag codes frequently are red herrings.  Look for the obvious :)

[K Frame]

Parts like that are reliable. Until they fail.

Over time the connector plugs can fail, the wires inside the insulation can break, or, for whatever reason, the probe can simply stop functioning.

I recently replaced the knock sensor on my 1997 Subaru because it kept throwing a code and causing the engine to run badly. It's an extremely simple part, essentially an acoustical pickup bolted to the top of the engine to check for detonation out of time with the computer controlled firing cycle.

Resistance tests showed it to be fine, the connector appeared to be in good shape (I cleaned it and made sure that it was making good contact), but the second I started the car, it threw the code.

Replacement part was $80, replacing it resulted in an improvement in fuel mileage of 3 mpg.

[280plus]

As a general mechanic and not an auto mechanic I know that whenever something doesn't work right after a repair the first thing to suspect is the repair having something to do with it. The forgot to reconnect or damage to the wires theories are both valid and probably where I'd start looking. You might just take it back to them and tell them it worked before but now it's not and see where it goes.

One time I had a car where they had to jack the engine up to replace the oilpan gasket and when they were done the backup lights stayed on. They had mashed the wires between the block and the frame when they jacked the motor and this in turn caused the lights to stay on because the bare wires exposed by the damaging of the insulation caused them to short together around the switch.

[Ben]

Thanks guys. I just did a cursory inspection and everything looks okay from the outside.

Over time the connector plugs can fail, the wires inside the insulation can break, or, for whatever reason, the probe can simply stop functioning.

And I think it might be the wires gone inside of the insulation. I did some more googling and that seems to be one of the more common occurrences for this sensor.

I have to be in the vicinity of the shop in a couple of days so I might see if a mechanic has a quick minute to verify. If they tell me I have to leave it or they need to charge me, I'll just get a new one myself. I just figure in case it turns out not to be the sensor, but something else throwing that code and it's related to the work, want to give them a quick look first so no one can say I screwed something up messing with it and voided the work warranty. :)


This is the one downside of my normal modus operandi of buying a vehicle new and then keeping it a long time. I'm really meticulous about general maintenance, and expect to get at least another 100K out of this engine. Unfortunately even with meticulous maintenance on the drivetrain, with age, little parts like this slowly start to nickel and dime you as they fail with age. ESPECIALLY pollution control components. Seems almost like those darn things are designed to fail after 7-10 years!

[FTA84]

Parts like that are reliable. Until they fail.

I agree.  It has been my experience that many parts are ready to fail and do so after being agitated.

Did the repair shop agitate something related to the IAT? Most likely. Will you be able to get it replaced for free? Probably not, unless there is obvious blatant signs of abuse to the device. 

[280plus]

It has been my experience that many parts are ready to fail and do so after being agitated.

Mine too, my mantra is if it goes because I was messing with it it just means it was ready to go anyways.

[K Frame]

To get to the timing belt the shop probably had to disassemble the air intake pathway, which may have required removal or repositioning of the sensor, unplugging the pigtail, etc.

Hard to tell, though, as I'm not all that familar with the Trooper.

In any event, though, unless it shows obvious signs of damage, chances are is an AW DAMMIT! failure, which is the failure that invariably happens either on the way home from, or soon after getting the car back from, the shop. Those are the ones caused by the gremlins that live in the garage and come out when the mechanic isn't looking.

[280plus]

I'll never forget my 1983 AMC Eagle. I had just finished putting a new idler arm on it and was all joyful because it was the last repair it needed. So I went over to the driver side to get in, grabbed the door handle to open the door and it promptly broke off in my hand.  :rolleyes:

 

[Tuco]

If a code is sent, it means the parameter read is out of spec.  Not always a bad sensor.
It could be that the sensor is connected and in perfect working condition, reporting a "situation", i.e. High Input.

If it was me, I'd reset the code and see if it comes back. 
Many times sensors will throw a code that is never seen again. 

If the car is running decently, make a note, reset it and look for another one in the next tank of fuel or so.

This may be as simple as a dirty MAFS (mass air flow sensor) or a poorly installed air filter or intake housing.
(disclaimer-  I've never been under the hood of any Trooper)

Are you running a K&N (or other oiled) air filter?

[Ben]

The car is running fine and idling smoothly. I'm using a standard air filter, which only has about 3k miles on it.

Where can one generally find the MAFS, and what does it look like?

[Nick1911]

The car is running fine and idling smoothly. I'm using a standard air filter, which only has about 3k miles on it.

Where can one generally find the MAFS, and what does it look like?

It's in the airflow path, between the filter and the throttle body, typically.

[Tuco]

Looking down the tube from the air box toward the throttle body:



This is from the Nissan Titan message board - But is fairly typical.

There is a specially labeled cleaner used on these - Don't touch it with WD40 or Carb Cleaner.

[Ben]

Nick, that appears to also be where the IAS is. What I fiddled with today was right at the intake/engine I and assumed that was the IAS. Would the MAFS then be between that and the air filter, or was I actually looking at the MAFS?

[Ben]

AH - Two COld Soakers posted as I asked. So are the MAFS and the IAS in the same unit?

[Jim147]

AH - Two COld Soakers posted as I asked. So are the MAFS and the IAS in the same unit?

No.

Your mass air flow will be a large piece that clamps into the intake hose between the filter and intake manifold with several wires.
The air temp sensor will be a small two wire screw in piece that should be located before the filter or maybe in the filter box.
One of these days I'll learn to post picks to make things like this easier to describe.

[CNYCacher]

MAFS:

[Ben]

Alrighty then -- back under the hood I go... :)

[Nick1911]

I have actually seen both units rolled into one aluminum body with one electrical clip.

But yea, as others have said, the MAF is usually this big lump that the hoses clamp on to for air intake, whereas the IAT just screws into the intake pipe at some point.  On my Fords, the IAT is cylinder shaped, about 3-4 inches long, and maybe .75-1" in diameter.

This has some good pics: http://www.kingenterprises.net/iat_pictures.htm

Also:

Q. Where is the IAT sensor for a 2000 isuzu trooper?

A. Follow the air intake from the air filter holder. along the inside(away from the radiator side), you need to remove the plastic baffle over the engine. Just before the intake turns into the engine, there is a wiring clip into the side of the intake. That is the IAT sensor.

[Marnoot]

I have actually seen both units rolled into one aluminum body with one electrical clip.

But yea, as others have said, the MAF is usually this big lump that the hoses clamp on to for air intake, whereas the IAT just screws into the intake pipe at some point.  On my Fords, the IAT is cylinder shaped, about 3-4 inches long, and maybe .75-1" in diameter.

This has some good pics: http://www.kingenterprises.net/iat_pictures.htm

Yep, in my model-year of Maxima the IAT is separate from the MAF, but starting the next year they are part of the same (much more expensive) assembly. So it differs between makes, models, and years.

[Ben]

Ah, okay then as per Nick's post I was looking at the IAT sensor.

[Tuco]

Now, before throwing replacement parts at a C.E.L., take the works out, spray it down with a can of Mass Air Flow Sensor Cleaner, put it back together tight and correct, replace the air filter while you're in there, and reset the light.

If the same code reappears, make a note of when and how (idling in traffic, open road) and report back.

When a code is thrown, it doesn't automatically mean the sensor is bad, it means the condition it is sensing is out of specification.