Hi Guys,

I have a 2017 XC90 T8 with 60k miles and have recently gotten a code p0171 showing 'System Too Lean Bank 1'. I have checked the following:
-air filter housing nice and tight
-no visible issue with intake system or any plumbing
-no 'whistling' or strange rpm behavior (normal idle at 800rpm)
-no issues with oil leaks or oil consumption

OBD2 scanner showing O2 Bank 1 sensor voltages at around 0.95V
-car has half a tank of gas but only range of 80miles (so probably running rich)
-I can smell a strong fuel smell at idle (so again car running rich)

From what I've ready on the forums/internet problem could be related to:
-oil trap clogged or problematic (although i don't hear a whistle or issue with idle)
-vaccum leak (don't hear anything abnormal and fuel trim doesn't dip when idle raised)
-idle issues - rough or variable (no issues here, car idles fine)
-O2 sensor faulty (Not sure how to tell if the O2 sensor is faulty: any suggestions on how to tell?)

Car seems to drive normal in all modes (actually just came back from long trip to Vegas with no issues) CEL turned on a couple days after.
Looking for some feedback on people that came across this and suggestions to try.

Thanks,
Steve

 

code says the o2 sensor is reading too much oxygen ( ie not enough fuel to use up the alotted air). Normally I'd start with testing for an intake air leak (hoses/tubing/pcv/MAF etc) including an inspection and possibly a smoke test but since you noted you smell gas suggests there's something going on with the fuel delivery system that needs to be checked out - ie erratic fuel pressure or possibly a leaky line for a fuel injector issue/injector seal etc. When you say you have an 80 mile range - what was the range before this issue cropped up?

 

-All parts of the intake were checked (hoses/tubing/pcv/MAF)
-PCV is not whistling, and the idle is normal

Yes the engine is running rich (computer is compensating for the lean condition by injecting more fuel)
-The range was normal before the issue cropped up (about 150-200mile on a half tank)
-As I said now it's at 80miles on half a tank so it looks like the computer is calculating that more fuel is needed and gas mileage is impacted

One thing I didn't mention is that I did the following maintenance on Dec 18th (about 2 weeks before the problem happened):
-cabin filter change
-engine air filter change
-spark plug change
-oil change

But the car ran perfectly in those 2 weeks and we did a big trip (1k miles) over the holidays too without issue

Very odd.. hoping it's maybe a bad 02 sensor or something. Have appointment at dealer on tuesday .. I guess we'll see.

 

usually a major fail of the front o2 sensor (aka the lamda sensor) will set off a CEL. Similarly issues with spark plugs/coils - I'd also expect a CEL but its possible for something odd like a plug not being fully tightened (easy enough to check). Still I'd be concerned of the fuel smell - to me that suggests a leak somewhere. Good luck and post up how you make out.

 

yes its very odd, I've done work on european cars for a long time and this situation is very unusual. I don't really see why a plug change could of possibly caused this issue (maybe it's a coincidence).
One thing to note, the plugs were really seized into the engine so I did have to use some special lubricant (similar to WD40) in the chamber around the plug to help loosen them up (there were alot of carbon deposits). So i'm not sure if the lubricant got introduced
into the chamber (cylinder area) and caused an issue (fouled something or a sensor) but usually that stuff burns off quickly.
The use of the lubricant was unavoidable as breaking a plug while trying to untighten it would of been a major issue for me and a very costly repair.

 

I'd probably pull the new plugs out just to have a look to see what the electrodes and gaps look like and whether there's any staining on the outside (metal and porcelin) that would suggest a poor seal into the head.

 

dealer did a smoke test and it looks like its the seals on the supercharger. They will have to replace them and they said they might replace the O2 sensor as well.

will let you know when the final repair is finished

 

Final analysis:
-Front O2 sensor replaced
-Seals on supercharger replaced

Also they did find that one of the engine mounts was bad during the inspection and replaced that.

Looks like the car is fine now.

 

Hi Steve,

I’m currently facing the same problem with my car (same as your car, same year, same miles, etc.)

Following a smoke test at the dealership, they changed the seals as well, and one of the engine mounts!

I did a 1k mile trip afterwards with no problem. Back home, 1 week after the long trip, I have a CEL with the same p0171 code (no impact at all on the driving).

You said that the dealership changed the front o2 sensor as well. Which isn’t my case.

Could you please tell me if your problem was definitely fixed since that date?

Many thanks.
Philippe

 

The repair involved changing:
-the front O2 sensor
-Supercharger seals

Since then no issues

 

Thank you for your reply!

do you know by any chance what made them change the O2 sensor? Did you have weird o2 voltage values or something else?

 

Do you happen to know what supercharger seals were replaced?

 

I’m having similar issues but not the strong fuel smell. My mechanic has done several smoke tests and only revealed a leak in the PSV and replaced it along with the oil trap. Besides the code, I don’t have any other signs of a problem but this code is a mystery. The mechanic is now suggesting it’s maybe an issue with a leak in the supercharger and a repair will be a minimum of $5k. I keep asking them to check the 02 sensor . This code has been going on periodically for 3 years. It’s so frustrating. Can I ask how much it was for you to replace the sensor and supercharger?

 

I've got same code but haven't yet investigated. What was the final cost to repair?