Check Engine Light (Code P0172) - what could cause it?

[Adnan]

Hi,

 

Driving downhill (Lake Tahoe, around 7000 feet altitude) with my foot off the gas pedal, the CEL suddenly came on. Engine felt fine as I applied gas, idle was normal and power, etc. all felt completely normal. Car is a 2002 Legacy Outback with barely 14,000 miles.

 

I had filled up the tank a few miles prior to that and wondered if this was perhaps related to not tightening the cap well? Anyway, since things seemed fine, I drove on (I know, a gamble) and pulled the code after getting home. P0172 is "Bank 1 too rich". The CEL hasn't come on again.

 

What can cause this to happen? It sounds like a fuel metering issue, caused either by an incorrect measurement in air flow or something related to barometric pressure. Could going downhill result in the engine management computer getting out of sync. with ambient pressure?

 

Any thoughts on this would be most welcome.

 

Thanks,

Adnan

[Legacy777]

Might just have been a hiccup in the fuel injection system. I'd just watch it, and see if it happens again.

[Johngenx]

You'll need to read the adaptation values to see what's going on, but a rich condition is typically a metering problem when it comes to air mass or volume and/or fuel pressure. Normally, the fuel pressure problem results in a lean condition, and an air mass metering problem results in rich running.

 

Don't panic yet. Wait and see if the CEL comes on again. If it comes on again, and stays on, then get serious about finding the problem. A rich or lean condition can ruin your catalytic converter.

[TheCorkans]

You'll need to read the adaptation values to see what's going on, but a rich condition is typically a metering problem when it comes to air mass or volume and/or fuel pressure. Normally, the fuel pressure problem results in a lean condition, and an air mass metering problem results in rich running.

 

Don't panic yet. Wait and see if the CEL comes on again. If it comes on again, and stays on, then get serious about finding the problem. A rich or lean condition can ruin your catalytic converter.

 

Hey! We are having all kinds of rough running problems with out 2001 Outback and it reads P0172 as well. We have a Digimoto OBDII that reads various parameters. Are there any other readings we can look at to diagnoce the problem? Also, what are the "adaptation values"? Any advice greatly appreciated!

 

Cheers!

[DOORSTOP]

Hi,

 

Driving downhill (Lake Tahoe, around 7000 feet altitude) with my foot off the gas pedal, the CEL suddenly came on. Engine felt fine as I applied gas, idle was normal and power, etc. all felt completely normal. Car is a 2002 Legacy Outback with barely 14,000 miles.

 

I had filled up the tank a few miles prior to that and wondered if this was perhaps related to not tightening the cap well? Anyway, since things seemed fine, I drove on (I know, a gamble) and pulled the code after getting home. P0172 is "Bank 1 too rich". The CEL hasn't come on again.

 

What can cause this to happen? It sounds like a fuel metering issue, caused either by an incorrect measurement in air flow or something related to barometric pressure. Could going downhill result in the engine management computer getting out of sync. with ambient pressure?

 

Any thoughts on this would be most welcome.

 

Thanks,

Adnan

 

Change the front O2 sensor,It's under $80.00, called a air fuel ratio sensor, Usually a bad front sensor will cause this code.Also there are updates from Subaru on your computer, I would take the serial number and call your local dealer and see if there are any updates available.It shouldnt be to expensive to update it.

[OB99W]

Hey! We are having all kinds of rough running problems with out 2001 Outback and it reads P0172 as well. We have a Digimoto OBDII that reads various parameters.[...]

If you can, obtain the freeze frame data; the short term fuel trim (STFT) and long term fuel trim (LTFT) can be especially useful.

[unibrook]

I have a 2001 Forester L with 85k miles on it. I have been chasing an intermittent hesitation under load problem for the past year. Only occurred when engine was warm. The front 02 sensor had been replaced once at 40k miles. I suspected it again this time, but since the only codes thrown had been cyl's 2&4 misfire ( p0302 & p0304) I assumed it must be ignition related. So I replaced plugs and wires 8 months ago...no effect. Did the dollar bill test over exhaust pipe, it was fine. Misted the coil, no sparks. I mentally sort of ruled out the fuel filter since it only happened when the engine was warm. Finally, a week ago while cruising on hwy at 65 mph, I felt the hesitation again (I wasn't even accelerating this time) and a new code was thrown....p0172. AutoZone read it for me, I described the symptoms to the guy and asked if he thought it might be the front 02 sensor. He said, "absolutely." So I decided to replace it next. Cost me $100.75 incl tax for the oem part# 22791aa00a from Cityside Subaru. I asked the Parts guy there if his experience was that this model engine needed a new front 02 sensor every 40k miles. He said, "no, these sensors are good for 100k miles." Well, bull************ on that. I replaced the new front 02 sensor in 1 hour reaching from the top over the passenger side of the engine using an adjustable wrench. Be sure to use the thread lube so you can get it out easily next time.....after another 40k miles. I took out the air channel assembly first for better access. That seems to be the fix. No further hesitation since. Car runs like new.