Car: 2009 Volvo XC70 T6 (3.0L)

I have been plagued with the dreaded check engine light. Recently I had a mechanic advise the DTC was P0171 (lean) and I needed to have my bank 1 O2 sensor replaced to fix. So I had the work done but it did not solve the problem. The light came back on the next day. I should have taken it back but did not trust the advice.

I decided to look around the engine and found a short hose off the air intake, just past the MAF sensor, disconnected; I was exciting thinking this was the smoking gun, so I secured it, cleared the code, but the code (P0171) came back the next day. Not sure if reconnecting the hose made a difference. The engine appears to idle and run well, no hesitation or rough idling,

The other item I noticed today, just under the air intake, but above the belts, was an oil residue. Not sure what the part is above the belt, but It has a connection at the end closest to the firewall with a hose that comes off and insulated with foam. This part, or sensor, that is connected to this part can be rotated and has some play and appears be where the oil is weeping from. Anyone know what this part may be? And, think it is related to the P0171 DTC?

 

You have a leaking brake vacuum pump. Not related to the code, which is likely a bad PCV breather box.

 

I've had the very same issue recently on an 06 S60 2.5T that we prepared for sale. We, too, changed the upstream oxygen sensor since it had high mileage anyway and appeared to be slow to respond to changes.

It turns out that yup, the brake vacuum pump is leaking. They are not that expensive and can be bought for around $125.