P0171 Lean on Bank 1 fault

Paulr · Post by **Paulr** » Wed Mar 15, 2017 11:59 pm

After the engine light came on I purchased a cheap OBDII reader and it gave me this code. It comes back again after two engine warm up cycles, which is what it is designed to do if there is a recurring fault.

There is so much info on the net it is overwhelming and confusing, but as far as I can tell bank 1 is the first three cylinders, and I think it could be MAF, a vacuum leak, or an 02 sensor (bank 1 02 sensor is the first sensor on the exhaust and before the cat?). The car runs perfectly so I don't think it is fuel pressure or timing.

Am I right in saying it is best to start with a smoke test by puffing smoke down the brake vacuum pipe & sort out any leaks that may show up, if there are no leaks clean the MAF, & finally then change the 02 sensor if nothing else works? Don't want to change the sensor and spend money unnecessarily, but equally I don't want to spend ages chasing an issue I could have sorted quickly!

Is that about right? Or is it simpler/more complex than that?

Smartbear · Post by **Smartbear** » Thu Mar 16, 2017 12:02 am

Hi, that's quite often caused by a torn elbow on the inlet rubber that connects to the throttle body, it's the small piece that spurs off that splits. It's very diy-able but fiddly due to the positioning of the securing clips

Rob

paddy wright · Post by **paddy wright** » Thu Mar 16, 2017 7:44 am

Smartbear wrote:Hi, that's quite often caused by a torn elbow on the inlet rubber that connects to the throttle body, it's the small piece that spurs off that splits. It's very diy-able but fiddly due to the positioning of the securing clips
Rob

Yep- will most likely be this- search rubber intake boot on here or you tube for how to guide. It is fairly straightforward job.

paddy wright · Post by **paddy wright** » Thu Mar 16, 2017 7:45 am

Smartbear wrote:Hi, that's quite often caused by a torn elbow on the inlet rubber that connects to the throttle body, it's the small piece that spurs off that splits. It's very diy-able but fiddly due to the positioning of the securing clips
Rob

Yep- will most likely be this- search rubber intake boot on here or you tube for how to guide. It is fairly a straightforward job.

Chris_D · Post by **Chris_D** » Thu Mar 16, 2017 7:51 am

+1 intake boot.
Had that code when i first got mine. A holy intake boot one of the issues i found on inspecting the car and formed part of the 500 quid discount i haggled hehe. As per pic below
As rob suggested the boot dries out over time and holes form where it branches off. If theyre big holes u will hear a 'chirruping' sound when engine is under load as the throttlebody opens up and sucks air in.
Part's cheap and very easy to replace and if ur going to DIY why not go the whole hog and inspect the disa condition and clean the tb and icv....
Only clean maf as a very last resort.

: Photo 30-08-2016 14 49 31.jpg (124.93 KiB) Viewed 1233 times

jabber · Post by **jabber** » Thu Mar 16, 2017 8:22 am

[quote="Chris_D"]+1 intake boot.
Had that code when i first got mine. A holy intake boot one of the issues i found on inspecting the car and formed part of the 500 quid discount i haggled hehe. As per pic below
As rob suggested the boot dries out over time and holes form where it branches off. If theyre big holes u will hear a 'chirruping' sound when engine is under load as the throttlebody opens up and sucks air in.
Part's cheap and very easy to replace and if ur going to DIY why not go the whole hog and inspect the disa condition and clean the tb and icv....
Only clean maf as a very last resort.
Photo 30-08-2016 14 49 31.jpg[/quote

This was the problem on mine

Number5 · Post by **Number5** » Thu Mar 16, 2017 9:26 am

This is what you're looking for.
The part is about £30 from a Main Dealer and takes about an hour to fit yourself.

Ducklakeview · Post by **Ducklakeview** » Thu Mar 16, 2017 10:46 am

Number5 wrote:This is what you're looking for.
The part is about £30 from a Main Dealer and takes about an hour to fit yourself.

That's what I call a "tested forum diagnosis"

Have to say also, that I'm surprised that is only £30 odd from BMW.. Was expecting at least £100!

Mike

Fox889 · Post by **Fox889** » Thu Mar 16, 2017 4:01 pm

Mike, I found BMW were cheaper for a jacking pad that had gone awol on mine, looked on eBay & they ranged around the £20 mark, went to my local main dealer, £12'ish, very surprised.
I too had a new elbow for mine & was very surprised by the cheapness, perhaps they're learning?

Paulr · Post by **Paulr** » Thu Mar 16, 2017 5:56 pm

Thanks for that, very useful. One thought though, it is only bank 1 that is affected, would that leak on that pipe not affect both banks so I would have P174 as well, or is that just a feed for bank 1?

Chris_D · Post by **Chris_D** » Thu Mar 16, 2017 11:44 pm

did u inspect intake boot for holes yet?
should be ur first port of call/fix. then see if that addreses the o2 issue....
can't remember if both banks on mine threw up codes.

Paulr · Post by **Paulr** » Thu Mar 16, 2017 11:47 pm

Been at work all evening, so will check the air intake boot tomorrow. Be great if this is the fix!

Thanks for the advice everyone, much appreciated.

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