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CEL Code P0172: Help Needed

Old 10-08-2008, 08:51 PM
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Default 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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Old 10-08-2008, 08:59 PM
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maybe the MAF sensor may need to be replaced
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Old 10-08-2008, 09:00 PM
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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.
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Old 10-08-2008, 09:42 PM
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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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Old 10-09-2008, 01:36 AM
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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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Old 10-09-2008, 01:39 AM
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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.
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Old 10-09-2008, 02:00 AM
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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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Old 10-09-2008, 02:01 AM
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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.
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Old 10-09-2008, 02:06 AM
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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.
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Old 10-09-2008, 04:35 AM
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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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Old 10-09-2008, 02:59 PM
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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.
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Old 10-09-2008, 06:19 PM
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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.
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Old 10-09-2008, 06:49 PM
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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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Old 10-09-2008, 08:48 PM
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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
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Old 10-09-2008, 08:51 PM
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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?
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Old 10-10-2008, 12:34 AM
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Originally Posted by sc_irony
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 02 sensor too and see if that helps. So I pulled the intake off and put it back on making sure there were no vaccum 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
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.
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Old 10-10-2008, 01:07 AM
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Originally Posted by drjohnson36
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.
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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Old 10-10-2008, 01:24 AM
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Originally Posted by toyoguy27
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 rest 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
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.
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Old 10-10-2008, 04:13 AM
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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...
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Old 10-10-2008, 06:28 AM
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Originally Posted by SCIONOSIS
Originally Posted by drjohnson36
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.
So it probably is or isn't the CTS, but the CTS signal does have alot 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 dtc P0171 (fuel system too lean). Ofcoarse, intake vacuum leaks introduces more air into the mixture creating a lean condition.
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.
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