2006 volvo s40 2.4i

So the dreaded p0171 code has come up after my engine replacement (which I did myself). The car is running really great though. No issues at idle, starting, or anything else.

I have tried finding a vacuum leak but haven't been able to find one. Sprayed carb cleaner at all vacuum/intake spots that I know of past the MAF sensor.

I cleaned the MAF sensor also.

I added fuel injector cleaner to gas tank.

I tried to tighten my o2 sensors more on the exhaust manifold, but they were already extra tight.


I was thinking about trying to do a smoke test, but am a little confused on where to blow the smoke into. Any help or suggestions on this? I don't have a smoke machine though so I was planning on doing the poor man's smoke test with a cigar or something.

An alternative I was thinking about was to hook a bicycle air pump to a part of the intake and pressurize the system a little while the car is off, and if it maintains pressure then I know there is no intake leak. However, I'm not sure if this would actually work nor where to hook the bike pump at.


Any suggestions on how to do smoke test, or pressure test?

Or any suggestions on what else to check? Because the car is running great I'm having trouble narrowing it down. I feel like everything should be running fine unless I have a bad 02 sensor or MAF sensor??

Thanks in advance!

 

There is no way cigar smoke would work and the bicycle pump idea won't work either. That code is for lower limit, which would not be a vacuum leak anyway. Make sure the oil is clean and not overfilled. Make sure you don't have high fuel pressure. Leaking injectors can cause it, but I've never seen it. Then take it to the dealer to make sure you don't need the ECM update. There is a bulletin for it for that code .

 

Bad fuel pressure regulator? Congrats on the engine replacement btw!

 

Thanks for the response. I'm not sure why lower limit would rule out intake leak. Can you explain this?

And should my pressure be around 55 give or take 5psi? Haven't tested it yet but looked up specs.

 

The code refers to what the ECM is doing to maintain correct air/fuel ratio. It adjusts by adding or subtracting fuel. Upper limit is set when the ECM has added too much fuel. It does this because there is too much air, like a vacuum leak. If there is too much fuel, like high fuel pressure, it tries to compensate by subtracting fuel. A dirty throttle can also cause this, because less air would be the same as excessive fuel.

I don't have the specs in front of me, but I believe 55 is correct.

 

My fuel pressure is good. Maintains a constant 55psi (~380kpa) at idle and at higher rpms (2,000 and 3,000). Thanks for suggestion.

 

Is that with a gauge or with data from the sensor via a scanner?

 

So I thought I almost had it. I feel like I am getting closer though.

Little history, engine was replaced because it was run with little oil and overheated. Cracked head and burnt coolant for the short amount of time that it was able to run.

I am thinking I may have bad O2 sensor or maybe more than one. Keep reading.

I got a scan tool that can show live data and got some more clues.

Fuel Trims
@ idle 750rpm
short - +25.8
long - +21.9

@2,000 rpm
short - +26.6
long - +.8

@3,000 rpm
short - +26.6
long - 0

Oxygen Sensors
Bank 1 Sensor 2
wave between .25 and .2 volts

Bank 1 Sensor 3
wave between .2 and .15 volts

Both respond quickly and max out around .9xx volts and then return to nearly 0 then back to values stated above.

Scan tool did not show a Bank 1 Sensor 1 (which I think is bad) The one at the top center of exhaust manifold correct?


So any ideas on what it may be or directions to go in?

 

That is with a gauge.

 

Can your scanner read calculated MAF vs. Actual?

 

No, reader just shows MAF reading (just one reading).

I cleaned fuel injectors today and swapped MAP sensor, Throttle body w/ sensor, and upper intake manifold to the ones from old engine just to see if there was a difference and there wasn't.

Also took out spark plugs and they looked to be in good shape.

I also tried to reset trims after clearing code by unplugging battery and then turning the key to try to start it, pushing radio on, windows, lights, blinkers etc.. then waiting 30 minutes, then repeating key, radio etc... then hooking battery back up. But trims were still high. I got excited at first because they were low but realized that the circuit was open and that when it was closed trims were back up high. Sigh.

I'm running out of ideas, which is probably a good thing as it is narrowing down.

Since I swapped out engine I had to take off exhaust manifold and cat, am now thinking what if there is a leak/vacuum pulling in fresh air causing a lean reading on the O2 sensors? But spark plugs didn't seem to indicate a rich condition. Grey with light brown tint on some spots. If there was a leak in exhaust, it would have to be before B1S1 sensor, right? Which would mean the exhaust manifold gasket.

But driving today and watching the fuel trims showed high trims at idle and coasting, but low (normal) trims while accelerating and on hills (higher loads).

Called dealer and was told that there were no recalls for my vehicle and that everything was up to date. How would they know that ecu is up to date? keep track with the VIN? Also was told that it is $138 to diagnose. Yikes.

 

Not sure where you heard about all that radio/window stuff to reset fuel trim, but that does nothing. With VIDA, the trim is reset when the codes are cleared. Apparently not the case with the aftermarket scanner. I'm also curious why B1S1 isn't showing up. Even if you unplug the sensor, it should still show up as a parameter. But again... Aftermarket scanner.

Did you replace the exhaust manifold gasket when you did the engine? If it was leaking, you should be able to see signs of soot coming from it.

The bulletin is not a recall. They would need to plug the car in to check the software.

I would ask the dealer why the diagnosis isn't free as part of the Volvo Service Advantage program

 

I think I read it was possible to reset on a couple posts, but I'm pretty sure it is only for older Volvo's. I just thought I'd try it. Didn't think it would work since no matter what I do, car never forgets radio stations. I'm sure it would keep the important information too.

Sorry I forgot to add this, oxygen sensor (A/F sensor) does show up. It just wasn't grouped with the other two and it was labeled a little differently.I'm not sure how (A/F sensors work or how to test them). I ordered one because I thought it wasn't working, but then I did a propane added to intake test and fuel trims dropped. But then I couldn't get it to happen again. I will try when I get home, maybe with a hose attached so I don't suck in too much air with it.

I didn't replace any exhaust gaskets. The cat gaskets are the easy ones to get too. I'll have to remove heat shield to be able to check for soot. I'll try soapy water test too but that probably won't be until tomorrow or the next day.

I'll call the dealer again. should I mention a bulletin for p0171? I'm sure they would be able to see if there was one or not right?

 

P0171 is a generic code, which we don't use. But it corresponds to ECM-250A. Just because there is a bulletin does not mean anything is free. Volvo advertises free diagnosis for warning lights as part of Volvo Service Advantage. If a software update is part of the repair, you have to pay for the update.

 

They are closed on weekends so I'll have to wait until Monday. I replaced the MAF with one from autozone which seemed to be branded with Toyota on it. The previous one was dirty and after cleaning it was getting MAF codes. Replaced and codes never came back. Do you think a non Volvo MAF can be the cause?

What should my MAF reading be at idle? That seems to be when I'm having the most issue. I can't find any specs specific for my vehicle, just people saying 4 f/s and others saying g/s

 

I don't know the spec off hand but with an aftermarket scanner, who knows if the data will even be what I'm used to. I think it's 4 g/s if I remember correctly. The more accurate way to check the MAF is with the Actual vs. Calculated

 

I fixed it! It was a vacuum leak due to unconnected hose from oil filter housing.

First off, ES6T...Thanks for your help and your time! A big help!

It is the small short elbow piece coming out of the driver side of the oil filter housing.
#10 to be exact from picture.

If anyone else is having same issues:

The big clue was that my fuel trims were high at idle and low/normal with throttle open (letting in more air). Read an article explaining why this is indicative of a vacuum leak. Basically the proportion of air from the leak is greater when at idle than when the throttle is open because the vacuum is sucking in relatively the same amount of air while the the air intake sucks in more air with throttle open. Since the proportion is now less it causes fuel trims to drop.

So check for vacuum leaks!

I did, but this car had one behind the air filter housing going from oil filter housing to lower intake manifold (not the pcv hose that most people refer to, but the short elbow hose) that I missed and continued to miss since it was hard to see (of course it's easy once you know to check it). Mine must have accidentally came off while trying to put lower intake manifold and air filter housing back on.

 

Nice job - finding that will no doubt increase the quality of your sleep by 200%! Thanks for sharing the outcome!