Hi Everyone,
I'm new here and am in need of help for a P0171 lean code on a 2001 Volvo S40 1.9T with 158k. The car came to me with this issue, and the previous owner said that the CEL has been on for 2 years now for that code. I replaced the breather box (it was clogged pretty bad at the drain), and I cleaned and inspected the breather hoses. I thought that would've fixed it however, no. The timing belt, and VVT gear were pretty bad and dumping oil everywhere, I replaced all that just out of the fact it needed to be done after 158k (I know, right?), along with all the seals. I did an oil change, OEM spark plugs, coils, wires, pre-cat O2 sensor (hasn't ever been done before) as well as the OE fuel filter which was pretty dirty. I reset the codes as well as disconnected the battery and put the leads together. I've smoke checked it many times for any and all vacuum leaks, did a compression check and cylinder leak down check, and no issues that I could see. I think the MAF is ok because when I disconnect it while running, the idle surges. I also vacuum checked the fuel pressure regulator with a mightyvac and it held pressure. It also does not give off a smell of fuel, so I think that it is alright. Last time I checked fuel pressure it was somewhere around 40psi, but that was before I did the fuel filter. The car runs awesome and idles very smooth, just eats gas because the ECU is trying to compensate for a lean condition. Any help is greatly appreciated. I don't think it's ever been to the dealer, I read somewhere that there was a fix for this lean condition by putting "extenders" in between the firewall connectors and O2 sensor connectors, as well as a firmware update.

 

Is the engine coming up to full normal operating temperature? A bad (open) thermostat could keep the ECU in the over-rich "warm up mode".

Normally a new pre-cat O2 (aka "air/fuel") sensor will clear up a host of issues if the old one was suspect (which isn't unusual over 100,000 miles). I suppose it's always possible that your new sensor isn't working correctly.

I would clean the MAF sensor thoroughly (no easier thing to try!).

I don't remember what my 2005 V50's fuel pressure was, but 40psi doesn't sound like it could be too far off (not familiar with your particular engine, of course).

 

Hi habbyguy, thanks for the input. I did clean the MAF sensor before, but it didn't change anything. I used a Bosch oxygen sensor (never had an issue with one of them). The outside air temp reading on the dash is --- (dashed out). Would you think the ECU looks at ambient air temp and changes engine parameters based on it?

 

There is 2 MAP sensor on that car.One on the intake manifold the other is on the top of the inter cooler.Check those out seeing how you checked/replaced the rest.