CEL Code P0172: Help Needed
 

Alright so I posted in the other thread but I could use some help so I don't buy the wrong part from the dealer today. Here's what has been going on:

I just put my Injen CAI on last Wednesday. Yesterday morning I go to start my car, it starts to fire up but then bogs down and dies. I crank it over again and it starts up, but a beautiful CEL light is glowing at me. Car seems to run pretty much like normal, but once this afternoon at a stoplight it was holding at 750rpm and then started bogging and tried to die. I came home disconnected the battery let it sit for awhile and then went out and reconnected everything. I started it up and the CEL went away and it seemed to be idling fine. I let it idle for around 6 minutes and then the fan kicked in but when the fan kicked off the motor shut off with it and the CEL came back on?
Sorry for the long read, thanks again.

So last night I changed the plugs and cleaned the MAF sensor and that didn't fix it. I pulled the code today and it was a P0172 (System too rich, Bank 1) I'm wondering is it the air/fuel sensor on the exhaust manifold I need to replace, or is it the O2 sensor on it I need to replace?

Any help would be appreciated because I don't wanna blow the money on the wrong part.

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maybe the MAF sensor may need to be replaced

i retract my last statement cause the MAF sensor can't tell whether you are lean or rich.. that can only be measured after the block.

Yea it says its running rich, and it's Bank 1 so its in the exhaust manifold. I just called the dealer and he wanted to know if I needed the O2 sensor in the manifold or the air/fuel sensor in it that looks a lot like an O2 sensor.
Does anyone know which one would be doing this? The O2 is 126 bucks and the air/fuel is 200 so I don't wanna get it wrong... :(

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Honestly it could be either one. My guess would be that the MAF is reading incorrectly. After that the O2 sensor determines that the engine is running too rich and tries to correct it which causes it to run really lean and stall.

What you could do is find a friend with a tC and swap the MAF over from his/her car. Let it run and test it, etc. If it works then you know your problem. If it doesn't then try the O2 sensor. If that doesn't work then you're SOL and have a bigger problem.

Just make sure that you test the MAF first. You don't want to foul out your buddy's O2 sensor and have to buy 2 of them.

Also as a side note the 05-06 MAF is different from the 07-09. I do believe the O2 sensors are the same though.

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also it says "BANK 1" not "bung 1" There is no bank 2 on an inline motor.

It goes bank 1, sensor 1. Bank 1 sensor 2. and on a V motor bank 2 sensor 1, and bank 2 sensor 2.

Sensor 1 is on the exhaust manifold. Snesor 2 is after the cat.

P0172 is MAF problem. And yes there is a Bank 1 sensor and there is a Bank 1 Sensor2. B1S1 is the a/f B1S2 is the O2. If the A/F was shot a P1125 would be there.
I would swap MAF and reset ECU memory. Do this by disconnection the POS and NEG of the battery and touch then together about 30 sec and then reconnect.
If you just swap the MAF and not clear memory it will take a while you relearn and you won't know if the problem is gone.

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when you installed your CAI you may have created vaccuum leaks in the induction system that the MAF sensor is not reading. Vacuum leaks will throw off the air/fuel ratio and confuse the ECM. The leak may be coming in flow right after the MAF sensor. I'd double check your install at that point first.

Also, look into the MAF sensor and check the resistor elements inside the chamber. If you see fuzz stuck around the element, it's dirty. You can take a chance and spray brake cleaner carefully into the chamber.

Alright thanks for all the suggestions guys. I'm gonna try to swap the MAF sensor from my buddies car and see if that helps. I'll swap the O2 sensor too and see if that helps. So I pulled the Intake off and put it back on making sure there were no vacuum leaks.
The car didn't have the problem of trying to die at idle anymore really and seemed to be running better when moving...however after test running I let it idle and was listening to the motor when the fan kicked on, when the fan kicked off the motor bogged down and died with it.

Also I have a K&N filter on it, would buying a dry flow filter be any more beneficial?

Thanks for the help guys this is a bummer :(

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^^^Fuel richness and cooling fans operation?

Sounds like a defective CTS (coolant temp sensor). The sensor is probably out of range and giving the ECM cold condition values when it not actually cold. Usually, the fuel trim runs rich when it recieves cold startup values from the CTS. The ECU also compares MAF sensor readings to CTS along with O2 sensor readings to trigger the DTC. Plus, CTS also has something to do with cooling fan control. Just putting my input out in the air and is all just speculation. So, you'll need a certified technician to verify this.

If the water temp sensor was fried, the temp gauge on the dash would stay at the bottom. I'm sure he would've noticed that if it was the problem.

Also... the A/F ratio runs rich at startup because the O2 sensors are too cold to operate, so the engine runs on an open loop (rich). Once they heat up, the sensors are able to function, and the engine starts closed loop operation (relies on sensor readings to adjust A/F ratio). As far as I'm aware, water temperature should have almost nothing to do with A/F ratio.

As for the OP's problem... definitely check for leaks around your intake. Either listen for a hissing, or spray soapy water and look for bubbles. If there are no leaks, check the MAF first, then check the O2. A funky A/F ratio could be caused by either, and either one will throw the same code you've described. BUT, if the sensors were defective, you'd also see other codes. I'm convinced it's a leak somewhere.

For some reason the MAF sensor is bad, I'll buy your bad MAF sensor.. lol I need a bad one.. but how many miles on the car? Try cleaning the MAF if that helps.

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Thanks for the responses guys. Yea it runs at normal operating temp. It also runs normal after like 3000 rpms it just hesitates up until that point almost as if it having a hard time getting a reading? I cleaned the MAF sensor and reset the ecu by disconnecting the battery..but I didn't clear the code. Would it have began running normal again or would I have had to clear the code to see if it worked? Also I've heard the little bulb is suppose to be amber. Mine was amber at parts but pretty black...would that make it bad? Ill check for vac leaks again today but I've found none on the intake so far

you disconnected the battery but it didnt clear the code? maybe you didnt disconnect it long enough? or the code just went back? which bulb are you talking about? in the maf?

I completely missed this part of your quote earlier, but this K&N filter might be part of the problem. I heard these filters have some kind of treatment that you use every time you clean & rinse the filter. Im not sure if it is oil based but that stuff can get sucked into the MAF sensor, rendering its signal values. Change it out for something other than K&N, clean the MAF again, clear the code, and test it out.

So it probably is or isn't the CTS, but the CTS signal does have a lot to do with the A/F ratio when you do cold startups. That and other signals that the ECU uses is used to calculate the amount of fuel delivery to a cold or even warm engine.
A rich running cold engine is not solely for the operating temps of the O2 sensor also. It can help warm up the O2 sensor faster, but the O2 sensor has its own heating element to do that.

I doubt it would be a vacuum leak cuz if it were, he'd have Code P0171 (fuel system too lean). Of coarse, Intake vacuum leaks introduces more air into the mixture creating a lean condition.

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Sensor 1 is an O2 sensor. Sensor 2 is an O2 sensor. Sensor 1 is used to determine the AFR. Sensor 2 is used to determine if the cat is working.

Do not touch the terminals together. Just take the negative terminal off, and try to start the car.

Also, a tip: If you have an alarm that works through the factory horn, pull the horn fuse before reconnecting the terminal. I can't tell you how many times i almost crapped myself because i forgot to pull it.

Thanks again for the replies guys. Im gonna go buy a dry flow air filter that doesn't require oil like the K&N, swap out the MAF with one from a buddies, clear the code and reset the ecu and see what that does for me...

I didn't say vacuum leak. I said a leak at the intake, after the MAF. If this were the case, the MAF would be telling the ECM that a greater amount of air is reaching the engine than there really is (due to the leak). Therefore, the ECM injects more fuel, running rich.

I've not seen a single car on any kind of fuel injection that relies on the water temp sensor to determine closed/open loop. The reason your exhaust smells like fuel when you start your car up early in the morning is cuz the O2 sensor is cold, and won't work until it hits at least 400 degrees. The water temp sensor shouldn't have a thing to do with the system. Old carbureted engines used a choke to cause the engine to run rich because cold fuel doesn't vaporize as easily as warm fuel (for inherently obvious reasons). The rich mixture allowed the engine to burn until it heated up, after which a thermostat would release the choke, causing a more lean A/F ratio. Fuel injected engines don't have this problem with vaporization because the fuel is atomized by the injector nozzle.

Also someone said something about the K&N. I had a buddy who fried his MAF cuz a little oil got on the sensor. Definitely check that.

About the first part of your quote... the conditions in the intake flow is either at atmospheric pressure or it is at negative pressure (vacuum) caused by the engine breathing. For it to leak from inside the intake to the outside to atmospheric pressure is very very rare unless it's boosted. So, I'm not quite sure what you are saying with that. If you say more air is coming in after the MAF sensor, how is that sensor picking that up when the leak does not pass thru that sensor. If that were to occur, a P0171 would trip instead.

As for the second part, I do agree that fuel vaporizes at the injector. But, for the ECU to be able to go into closed loop, it has to know engine temps thru the CTS first. So yeah, CTS signal is vital information for the engine to operate efficiently in its environment.

I forgot to post about this in my last post. DONT do that. Bubbles need pressure to form, not vacuum. So if anything, those bubbles will form inside your intake.

There is a primitive way to check for leaks in your intake. This is to take a propane torch and blow propane (not a flame) around the intake. If the rpm's jump or dip, you found your leak. I don't recommend doing this though.

Alright so I pulled out the MAF and the bulb inside it is partially amber and the rest is black?
Did the oil cake itself onto it, or is the MAF fried? Either would that be the problem?

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^ That bulb color is normal. However, the bulb part of the MAF sensor is not the only thing you would clean. If you look down the hollow chamber next to the bulb with a flashlight, you'll see another element of the sensor. I believe that part of the sensor is what determines air temperature, density, and humidity. Like one other guy said, clean that other element you did not see with sparing amounts of brake cleaner. It's not recommended to do so, but it doesn't hurt to see if it will correct the problem if it's just a dirty MAF sensor. Brake cleaner evaporates quickly, but when you spray inside the chamber with a straw attached to the spray nozzle, be careful that you don't poke the element with the straw. Also, spray inside the chamber with the opening facing the ground. That way the grime washes out the sensor. If this does not correct your problem with a different filter, I recommend you take it to a certified mechanic in your local area. They'll do a complete test and inspection of other components related to that DTC P0172.

Don't forget to follow up here once your problem is fixed.

Ok so I just measured the resistance on my O2 sensor on the exhaust mani and it was only 3.7 ohms....that's probably the problem isn't it?

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light is now off Ill update when the light stays off for awhile

P0172
 

Hey, so what was the actual problem you had, and how did you solve it. I'm having a similar problem with Code P0172, car doesn't die but does seem to hesitate and stutter a bit at around 3000rpm.
Also feels like lost a bit of power. Car was running fine until I took off the intake to clean the throttle, after that it started to act weird and the code came on.

Any help would be greatly appreciated.

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The OP sc irony hasn't been on this Site for 9 years and is unlikely to answer you.

I would read > Page 1, Post 7 by toyoguy27 Dated 10-08-2008, 07:00 PM ▲▲ LOOK UP! ▲▲ to page 1

I am not a Tech, but according to his Profile (Click on his User Name) he says he is a Toyota Master Technician, so I would lend credence to what he said:

He says that "Code P0172 is a MAF problem. And you should Reset your ECU by disconnection the POS and NEG of the battery and touch then together about 30 sec and then reconnect."
It's possible when you took off the Intake, you might have accidentally contaminated the MAF Sensor. Try Cleaning your MAF Sensor and Resetting your ECU to relearn.

How to Detect and Clean a Faulty Mass Airflow Sensor

No Guarantee, but worth a try.

MR LUV
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P0172
 

Thanks for the reply, i actually did take out the MAF sensor and cleaned it with mfa cleaner, put it back on and drove to work the next morning, light still came on. Disconnected the battery during lunch for a minute or two but didn't touch the pos and neg terminals together. Should i try it again and is that safe to do?

toyoguy27 says in Post # 7: "I would swap MAF and reset ECU memory. Do this by disconnection the POS and NEG of the battery and touch then together about 30 sec and then reconnect."

Go4shoped in Post # 18 says "Do not touch the terminals together". "Just take the negative terminal off, and try to start the car."

toyoguy27 in his Profile says he is a Toyota Master Technician. So there is No Consensus on whether that is Safe or Not.

Perhaps, it's Safer to wait until someone else chimes in on the Subject and see if anyone else has experience the same problem?

And use the Infinite Scroll to Review the Related Threads Below. And also try using:

Sticky How To Advanced Search SL (Scion Life)

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P0172
 

Ok will wait and do some more research thanks

https://cimg8.ibsrv.net/gimg/www.sci...c660763aed.jpg

That's all I can find on the Code P0172.

I would Concentrate on the Possible Causes, One by One, as a Process of Elimination.

Hope it Helps,

MR LUV

P0172
 

Thanks, i will look into those causes, hopefully is nothing major

P0172
 

Oh btw what's the best and easy way to check for any leaks around the intake area

See> Post # 12 by drjohnson36 Dated 10-09-2008, 11:19 AM
See> Post # 22 by Go4shoped Dated 10-10-2008, 09:59 AM

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you may have wasted the maf using brake cleaner on it...should have used maf cleaner to begin with...my 2

P0172
 

I didn't use brake cleaner, i specifically stated that i used maf sensor cleaner. Anyways i maneged to fix the problem by just unscrewing the air intake and putting it back to getting making sure everything was tight, also had to cut the end of one of the hoses that leads to the intake from the throttle because it was kind of cracked from one end. The. I disconnected the battery for a couple of hours to reset the ECU and the car is running normal again with no code.

ok, my bad...some one in this post said they did...thought it was you...sorry...glad you worked it out...had the same thing with the cracked, rotted vac hose myself...probably the same one...little short one with a 90 degree bend that is hard to see behind the switch mounted to the intake tube behind the maf sensor??? i fixed it once, then replaced all of them suckas

P0172
 

Lol yup it was that same exact one. Yea im glad i decided to take another look at it myself cause i was just about to have a mechanic look at it.

Took me two gas caps, a cap gasket and a few pulled hairs before I found it...my crack was on the back side where you needed a mirror to see it...I looked at that little biaaatch, and all the other what 2hoses in the entire system, several times before the mirror showed me the defect