Air Temp Sensor

NachaLuva · Post by **NachaLuva** » Mon Jan 23, 2012 3:48 pm

I have an engine warning code... #26, air temp sensor.

I have noticed a few times its idling faster than it should, suggesting the choke is on, plus its using too much fuel, so that makes sense.

I took it out & hooked up my multimeter.

On the 20k ohm setting, it reads 1.78 at room temperature. After I've been warming it in my hand for a few minutes, it reads 1.52.

So is that 17,800 ohms & 15,200 ohms? Does anyone know what the air temp sensor's resistance is meant to be?

Also, how do I read my multimeter? Its been a while lol

Then I cleaned the terminals thoroughly, & put it back in. double checked the terminals were plugged together fully.

Then warmed up the engine & reset the codes...or at least tried to but it wont reset!

What do I do now?

Gannon · Post by **Gannon** » Mon Jan 23, 2012 4:46 pm

It should be between 2k ohm and 3k ohm at 20degC. If it is open circuit you could be getting a reading through your fingers, be sure to use alligator clips or similar for testing to avoid false readings.

GOD · Post by **GOD** » Mon Jan 23, 2012 5:45 pm

Just measured the IAT off my 1999 Forester engine - 1.53k ohms at (warm) ambient, 1.06k ohms when dipped in hot tap water. No idea if that's what it should be though

Dane.

pitrack_1 · Post by **pitrack_1** » Mon Jan 23, 2012 5:52 pm

nachaluva wrote: I took it out & hooked up my multimeter.

On the 20k ohm setting, it reads 1.78 at room temperature. After I've been warming it in my hand for a few minutes, it reads 1.52.

So is that 17,800 ohms & 15,200 ohms? Does anyone know what the air temp sensor's resistance is meant to be?

Also, how do I read my multimeter? Its been a while lol

Then I cleaned the terminals thoroughly, & put it back in. double checked the terminals were plugged together fully.

Then warmed up the engine & reset the codes...or at least tried to but it wont reset!

What do I do now?

Sounds like you are using the multimeter OK (assuming not fingers like Gannon said) ... 1.78 and 1.52 will be 1.78 kOhms (1780 Ohms) and 1.52 kOhms (1520 Ohms) respectively.

Can't help you with the actual required value, but Gannon's already commented. You may also wish to backprobe the actual plug to check that it is supplying the correct voltage. Use the multimeter on a DC voltage setting such as 20V DC. The impedance (resistance) the multimeter should provide to the circuit is 1MOhm (1000kOhms) or even 10MOhm (recommended) in the case of a good multimeter. Unsure if you need to do this with the engine running but in test mode (hope you know how to activate it for your vehicle) or if you can do it with the ignition on but engine stopped.

A workshop manual or sounds like Gannon should be able to advise further on this? Do you know someone else with the same model with a working one to check against?

Real speculation: One way to determine what the resistance could be may be to connect a variable resistor (preferably decade box) and adjust the resistance until the light goes out. I guess this would be in the range of 0 to 20kOhms (20000 Ohms). A 10kOhm potentiometer may suffice. Assumes you know what you're doing! Leave this to a last resort.

Gannon · Post by **Gannon** » Mon Jan 23, 2012 8:17 pm

Yeah I was using the values from the 2001 Forester FSM.

Chances are its just a NTC thermistor, and i was gonna guess it was a 3K type, which is what its resistance is at 25deg, decreasing as temperature increases. But given that you measured 1.5k at ambient, it could be a 2K type too.

I'll measure the one on our Foz and get back tomorrow.

NachaLuva · Post by **NachaLuva** » Tue Jan 24, 2012 1:12 pm

haha no not fingers lol, insulated probes.

Thanks for that guys. Will be interested what it is on your Foz Gannon.

The volts were 4.99V, same engine on & ignition on/engine off. Is that the correct voltage?

Do you think I should just get a new sensor?

Gannon · Post by **Gannon** » Tue Jan 24, 2012 6:56 pm

I just measured the one in our 04 Foz and it was 1.67k at around 25degC

If you are getting 5v at the sensor socket, this sounds like the harness is ok too

NachaLuva · Post by **NachaLuva** » Tue Jan 24, 2012 8:49 pm

So its meant to be 5V? Just sounds a funny voltage.

So if the voltage is right & the resistance is right, why cant I clear the code?

Gannon · Post by **Gannon** » Tue Jan 24, 2012 9:48 pm

5v is the standard for sensor voltage. As for why its throwing a code, thats a good question.

RSR 555 · Post by **RSR 555** » Wed Jan 25, 2012 2:53 am

Really need to check that you're clearing the codes correctly.

How are you doing it? and is it from the manual?

NachaLuva · Post by **NachaLuva** » Wed Jan 25, 2012 12:10 pm

Drove the car till at operating temp. Turned off then connected black plugs. turned ignition on, engine off, held throttle down fully for 5sec then released. Started car & drove at 60kmh for couple minutes.

Engine light never stopped flashing code

I would prefer not to use battery disconnect method if possible...

RSR 555 · Post by **RSR 555** » Wed Jan 25, 2012 12:53 pm

Ok.. if you did it like this then your codes are still in memory.

You need to connect the black plugs, start the car, drive the car for more than 2 minutes above 15km/h, then once the ECU light starts flashing constantly, you need to stop the car and hold the revs at 2,000rpm for 1 minute, then shutdown and disconnect. Now they are cleared.

Disconnected the battery is not the desired methold but will work non the less.

Gannon · Post by **Gannon** » Wed Jan 25, 2012 2:15 pm

I dont recall having to do all that when I cleared my o2 sensor code in my 01 Outback. I think I just connected both the black and green connectors, turned ignition to on, and then back off again.

The idea of the drive and rev of engine is to make the ECU use every engine sensor, and this will cause a current problem to show up again as a fault

NachaLuva · Post by **NachaLuva** » Wed Jan 25, 2012 4:22 pm

Got it from here:
showthread.php?t=14372

quote:
How to reset the ECU:
To erase trouble codes from the computer you have two ways. The first I have not verified, but I'm sure it works.
ECU clear memory procedure is as follows for auto and manual transmissions:
1. With engine at operating temperature, turn engine off. Place gear shift lever into park (auto transmission cars only).
· Locate the two ECU check connectors, for most cars they are located under the steering column and consist of a black plastic male and female connector, and a green male female connector. The exact location of the connectors varies with the different year models, but generally they are located under the steering column on the drivers side.
NOTE: sometimes they are still taped over with some small amount of plastic tape, so look hard, they will be there!
With the ignition OFF connect black to black and green to green.
· Turn on ignition, do not start the engine, (and for auto transmission, cycle the gearshift lever from park to neutral and back to park ), depress the accelerator pedal to full throttle and hold for a few seconds, and then release. Start engine and then drive for at least one minute, keeping road speed above 10 mph.
· ECU is now re-set.
· At this point the check engine light should start to flash the all clear signal (steady 1/2 second interval flashes). If the check engine light does not flash, or indicates some other sequence, there is a fault present in the system, and should be checked for necessary repairs.
· Once done, stop the car and turn off the engine.
· Disconnect the plugs.

Here is the same:
http://www.scoobypedia.co.uk/index.php/ ... e/ECUReset

Quote:
Classic (JECS) ECU Reset

Ensure engine is at normal operating temperature, turn engine off
Locate the two ECU connectors, located under the steering column and consist of a black plastic male and female connector, and a green male female connector
With the ignition OFF connect black to black and green to green.
Turn on ignition, do not start the engine, depress the accelerator pedal to full throttle, then return it to the half-throttle position and hold for a few seconds, and then release
Engine Check lamp turns on
Start engine and then drive for at least one minute, keeping road speed above 11 Km/h.
ECU is now re-set.
At this point the check engine light should start to flash the all clear signal (steady 1/2 second interval flashes). If the check engine light does not flash, or indicates some other sequence, there is a fault present in the system, and should be professionally checked for necessary repairs.
Stop the car and turn off the engine.
Disconnect the black and green connectors.
Job complete

Bugger! I missed the green plugs bit! D'oh!!!

I'll try Gannon's method 1st as its simpler, if it doesn't work then Paul's.

NachaLuva · Post by **NachaLuva** » Wed Jan 25, 2012 6:55 pm

I tried the easy way of just connecting black plugs & green plugs, then cycling ignition on then off...no luck.

So then I tried the way mentioned above...worked fine...no more codes

Thanks for everyone's help

Question now is, if the code came about due to me disconnecting the air temp sensor to remove the air filter box, ie, there's no fault, then why is my fuel consumption so high?

RSR 555 · Post by **RSR 555** » Wed Jan 25, 2012 7:04 pm

The code will only come back if you disconnect that AIT sensor when the ignition is on. Keep it off and you'll have no issues.

Gannon, if the trouble code comes on when driving then no matter what you do, you'll never stop it.

Gannon · Post by **Gannon** » Wed Jan 25, 2012 8:51 pm

RSR 555 wrote: Gannon, if the trouble code comes on when driving then no matter what you do, you'll never stop it.

I didnt explain myself very well, what I meant was that if the code was cleared, and the car was handed straight back to the customer, the code could reappear as they drove off, so the FSM states to drive the car a certain way, that ensures the ECU uses all sensors, as some are ignored until the engine is warm, or under a certain speed.

This is of course a guess

YouTube · Post by **El_Freddo** » Sat Jan 28, 2012 9:14 am

RSR 555 wrote:Ok.. if you did it like this then your codes are still in memory.

You need to connect the black plugs, start the car, drive the car for more than 2 minutes above 15km/h, then once the ECU light starts flashing constantly, you need to stop the car and hold the revs at 2,000rpm for 1 minute, then shutdown and disconnect. Now they are cleared.

You forgot about the part where you get out of the car and do a ritual dance around the subi for the blessing of the subi gods

I wonder who came up with that procedure??

Cheers

Bennie

NachaLuva · Post by **NachaLuva** » Sat Jan 28, 2012 12:30 pm

El_Freddo wrote:You forgot about the part where you get out of the car and do a ritual dance around the subi for the blessing of the subi gods

I wonder who came up with that procedure??

Yep I did the dance, but it was before & was more of a fist-shaking, swearing, muttering kinda dance lol

Some procedures are pretty weird, like this & the one to recode your keyless remote

RSR 555 · Post by **RSR 555** » Tue Jan 31, 2012 12:02 pm

Gannon wrote:I didnt explain myself very well, what I meant was that if the code was cleared, and the car was handed straight back to the customer, the code could reappear as they drove off, so the FSM states to drive the car a certain way, that ensures the ECU uses all sensors, as some are ignored until the engine is warm, or under a certain speed.

This is of course a guess

Yeah. Sorry but that's the idea of clearing them, so you can find out the current ones and fix before handing back the car. I understood what you meant but I too can't explain it well typing it.

El_Freddo wrote:You forgot about the part where you get out of the car and do a ritual dance around the subi for the blessing of the subi gods

I wonder who came up with that procedure??

Cheers

Bennie

Some Japanese g33k