Hello

I know this topic has been discussed in depth and there are so many possibilities, but I am looking for help with the little old P0171 code.

I recently purchased a 2015 Xc70 T5 with only 43k miles. It has only been driven like 5k miles in the past 3 years.

When I purchased it it was missing the gas cap. I don't know why. 😕 The check engine light was on. I figured ok the cel light had to be gas cap related as the car checked out great.I purchased an aftermarket gas cap. 3 days later the CEL turned off , awesome.


Yesterday it popped back on, EEEK. Just to cover all bases I should note the day before I did go through a car wash that blasted the underside.
I had the codes read today and they came in this order

1. P0171 "STORED" DTC SEVERERITY 2/3 system too lean
2.P0455 "STORED "evaporative system leak
3. P0171 "Pending" system too lean
4. P0171 "Permanent " system too lean

I'm pretty handy but not a diagnostician. Is that a word?

Everything I have read, it seems like there is no one single answer and it sounds like shops start throwing parts at it until they find the fix.
I can't afford to pay a shop to do that, so thought maybe I'd ask you all fine folks what cheap options I can start with myself.

I do not see nor hear any vacuum leaks. The Air filter is pretty dirty and I'm guessing original as all of the foam has disintegrated off the bottom. I ordered one and will replace this week. I'm having a hard time believing that could be the culprit though.

Only other thing to note,the car does have a burning smell. There are no oil leaks and it doesn't really smell like burning oil or rubber. I can't really describe it. I'm hoping it's just dirt, leaves dust burning from sitting so long.

Thanks for reading and any advice.

No one has chimed in but figured I'll give an update should someone else have the same issue.

I took it to an indie shop. They performed a couple of tests and even smoke tested it. It all came back good. They determined it is most likely a "sleepy" front oxygen sensor. They noticed the fuel trims looked great at idle but at 2000 rpms, they went crazy. Ordered the part, hope that takes care of it.

In regard to the burning smell, they could not find anything that would cause it. I'm wondering if the car running lean would cause the exhaust to get extra hot producing that smell.

Haven't experienced the sleepy O2 sensor symptom but have heard that replacement can clear the problem. Any changes in gas mileage?

When I had CEL, I replaced the gas cap seal with a Viton part and insured the filler neck surface was clean and free of any blemishes. Solved the problem and CEL is off.

Let us know if O2 sensor replacement solves the issue.

Quick update.
Oxygen sensor was replaced. Adaptations reset and couple hundred miles later still no cel and my mpg has gone up dramatically. Yay