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 Post subject: P0172 System Too Rich (Bank 1) - Need help!
PostPosted: Mon Jul 02, 2018 7:48 pm 
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Vehicle: MY13 2.5iS

Posts: 6
Location: Melbourne
Hi guys,

My first post here, unfortunately not the way i wanted to introduce myself but I already have a problem with my foz after only a week of ownership :cry:

We purchased our Foz 2013 2.5iS in great condition with 90,000km on the clock. Full service history with no prior issues. All was running well for about a week or so until the CEL came on with all the 'check hill descent control... etc' warning up on center console, cruise, eyesight disable and stuck in S mode. A visit later to Subaru and they pulled the P0172 OBDII code which implies that the system is running too rich.

They did an upper engine clean and cleared the code - it came back on a few hours after i picked it up.

I had the code cleared again and shortly thereafter cleaned the MAF with MAF cleaner. Again, later that day the CEL returned. From my understanding, the rich condition could be due to a number of things:

1. Faulty MAF
2. Faulty O2 sensor
3. Vacuum leak
4. Leaking injector
5. Worn spark plugs

I've ruled out 1 for now (unless the clean was in vein due to an actual faulty sensor), but not keen on replacing too many bits without good reason to. I've read of guys replacing many expensive bits and then ultimately it was a vacuum leak that was causing the condition. I'd also rather not provide a subaru dealer an opportunity to take me to the cleaners considering they couldn't pinpoint the fault after two visits.

Probably worth mentioning fuel economy to me seems pretty average. City and local driving is return around 12.5l/100km which seems quite high.

I just purchased a good quality OBDII bluetooth reader so will be plugging it in to have a look at some of the engine parameters to see if i can pinpoint something out of the ordinary.

Hoping some of you guys may have come across this issue before, or have some good info you can share to assist with my troubleshooting. Anywhere or anything i should be looking at/for?

Appreciate any help!

Thanks in advance.
Adam :thumbs:


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 Post subject: Re: P0172 System Too Rich (Bank 1) - Need help!
PostPosted: Mon Jul 02, 2018 8:10 pm 
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Vehicle: MY08 XT (SH)

Posts: 1277
Location: Brisbane
Just throwing ideas around here:-

Faulty O2 sensor seems likely to me.

If you can get your hands on another one (not nec. purchasing it - eg the shop might have a spare or "acquire" one from another customer's car for a bit) you could run that for a few hours to see if the problem comes back.

With the fast repeat-ability of the fault that has demonstrated itself so far you should know pretty soon if the replacement sensor has fixed it or not.

If there are two sensors (like the SH) start with the one closest to the engine because that gets beaten up the most. If there are more than 2, go about things logically I suppose (start with the named problem bank).

[If you don't mind some DIY, a 22mm ring spanner, the loaner 02 sensor and some work in your own time might save paying for shop hours.]

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 Post subject: Re: P0172 System Too Rich (Bank 1) - Need help!
PostPosted: Wed Jul 04, 2018 10:22 am 
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Vehicle: MY13 2.5iS

Posts: 6
Location: Melbourne
Thanks Yowie.

I might have a chat to my dealer to see if this is possible. Otherwise there are a couple of wreckers nearby, might be able to source a low km O2 sensor from there.

I am getting my OBD2 reader today - any readings from that which might indicate the source?


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 Post subject: Re: P0172 System Too Rich (Bank 1) - Need help!
PostPosted: Wed Jul 04, 2018 10:38 am 
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Vehicle: MY08 XT (SH)

Posts: 1277
Location: Brisbane
Depends on the OBD2 reader, but chances are the fault code info spat up will be less specific than the info from the expensive Subaru-specific reader the dealer used.

If you're getting an OBD2/bluetooth/Android (or whatever) perimeters display setup rather than just a "fault code reader" you might be able to set up one of the virtual gauges to show AFR (or lambda voltage or whatever the app calls it) to see how it behaves during normal driving.

14.7:1 AFR (approx - hovering around it) is normal behaviour in idle, cruise and light load conditions (once the engine is up to operating temperature). Richer than 14.7:1 in those conditions would be more evidence pointing to a faulty O2 sensor, but not guaranteeing that is the problem.

Also, under vacuum conditions (i.e no boost) if it's running rich you can probably rule out a vacuum leak. Presumably it would run lean under vaccuum if there were a leak because extra unmetered air is being sucked in somewhere.

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 Post subject: Re: P0172 System Too Rich (Bank 1) - Need help!
PostPosted: Thu Jul 05, 2018 7:28 am 
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Vehicle: MY13 2.5iS

Posts: 6
Location: Melbourne
Thanks for the reply mate.

Do you think its worth taking to an auto elec? Can they determine if an O2 sensor is on its way out?


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 Post subject: Re: P0172 System Too Rich (Bank 1) - Need help!
PostPosted: Thu Jul 05, 2018 10:13 am 
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Vehicle: MY08 XT (SH)

Posts: 1277
Location: Brisbane
Probably not.

If your car is anything like an SH, changing the O2 sensors is a 10 minute job. The only embuggerance is the cost of a replacement 02 sensor (of it turns out not to be that) or the scrounging required to convince someone to let you borrow theirs for a bit.

Auto-sparky call-out fees would need to be weighed up against 02-swap cost/inconvenience and the likelihood of success (estimated to be high). Perhaps chat to one for his/her thoughts though. Bram (on Ozfoz here) is an auto-sparky and might chip in on this thread if we're lucky.

Obviously, if you spend x amount of money/effort swapping sensors and it's not solved the problem that can be frustrating and you'll need to weigh up the options again from there.

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 Post subject: Re: P0172 System Too Rich (Bank 1) - Need help!
PostPosted: Sun Jul 08, 2018 12:23 pm 
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Vehicle: MY13 2.5iS

Posts: 6
Location: Melbourne
Think i may just have to bite the bullet and have subaru diagnose then i can source and replace the parts myself.

Hooked up the obd reader and noticed my short term fuel trim at idle was maxed at -29.7%. This doesn't sound right. Also noticed that the CEL always returns at low rpm or idle.


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 Post subject: Re: P0172 System Too Rich (Bank 1) - Need help!
PostPosted: Sat Jul 21, 2018 10:30 am 
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Vehicle: MY13 2.5iS

Posts: 6
Location: Melbourne
***Update***

Car back today. All spark plugs were found fouled, which they assume is due to incorrect af sensor readings. So have also ordered a new af sensor from bursons at half the price subaru were going to charge. Fuel trims back to normal. Happy days :thumbs:


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 Post subject: Re: P0172 System Too Rich (Bank 1) - Need help!
PostPosted: Mon Jul 30, 2018 2:12 pm 
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I Say: Beer, its so much more than a breakfast drink
Vehicle: MY10 XTP & MY00 GT

Posts: 482
Location: Central Coast - NSW
Interesting. I had my money on a vacuum leak.
I had this error when a BOV return hose was not connected back after an upper engine clean.

but alls well that ends well.

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 Post subject: Re: P0172 System Too Rich (Bank 1) - Need help!
PostPosted: Mon Jul 30, 2018 2:21 pm 
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Vehicle: MY08 XT (SH)

Posts: 1277
Location: Brisbane
JazzyJ wrote:
Interesting. I had my money on a vacuum leak.
I had this error when a BOV return hose was not connected back after an upper engine clean.
...


When that happened to mine i found it idled lean (producing lean idle error code) AND wouldn't hold full boost (presumably too rich under boost).

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