2001 Volvo s40 p0101code, mas air flow

[Chickmcgee]

I have a 2001 Volvo s40 which was throwing a whole bunch of different check engine light codes. After finding out the issues and replacing multiple parts I still have one code left, P0101. I have replaced the mass airflow sensor for this code and I have also learned that the upper CO2 sensor will also go bad by this code by replacing these parts the car is running much better but occasionally will die and the car does not seem to have the power that used to. I have also replaced the map sensor which is located on the top of the intercooler. I also heard that there is another map sensor by the fuel rail that I might try swapping that sensor as well to see if that fixes my problem. Any thoughts on why I'm throwing this check engine light code would help greatly thank you!

 

[Chickmcgee]

Another issue that I have learned that could be throwing this code is the fuel pressure regulator but I've replace this part a couple months ago and that is no longer an issue. Check that intake Boots for cracks and vacuum lakes and still nothing. Next I'm also going to look into replacing the idle air control valve or IAC valve, if present on this vehicle.

 

[The_Jeff]

If you have a vacuum leak the MAF won't see an idle's worth of idle air and will throw a code. If yours is like my 940 there are lots of hoses all over. I just went through this with it idling slower and slower until it would just up and die.

I wouldn't throw parts at it yet, the IAC has nothing to do with your idle except for possibly reacting when things get "too low" because fuel is being sparsely metered to go with a very low MAF reading.

Volvo is kind of dumb with their programming; allowing a very low MAF reading to appear legitimate. Does it idle well with the MAF disconnected?

 

[Astro14]

I think the S40 is Drive by wire - no IAC...so, the MAF is likely the cause - disconnect it, put the engine in open loop and see if it's better. If the engine runs better with the MAF disconnected, then it's likely the MAF - you can try cleaning it (MAF cleaner only, no other chemicals), but that often doesn't work. If you get a new MAF, get a Bosch or Volvo part...the aftermarket ones have problems...

 

[Chickmcgee]

The MAF brand new

 

[The_Jeff]

Originally Posted By: Astro14
I think the S40 is Drive by wire - no IAC...so, the MAF is likely the cause - disconnect it, put the engine in open loop and see if it's better. If the engine runs better with the MAF disconnected, then it's likely the MAF - you can try cleaning it (MAF cleaner only, no other chemicals), but that often doesn't work. If you get a new MAF, get a Bosch or Volvo part...the aftermarket ones have problems...


A volvo (at least of my vintage) with an unplugged MAF isn't so much open loop as fail safe, about all it can do is idle! I would not indict the MAF on its unpluggedness alone.

OP would do well to get a better scan tool that shows live data. Also wander around the underhood with an unlit propane torch in case it helps idling through a vacuum leak.

 

[Chickmcgee]

I have checked for a vacuum leak around the intake manifold with brake cleaner and while it is idling, I would spray around my intake hoses and vacuum lines and it does not idle up while spraying the brake cleaner

 

[Vikas]

I had never heard of brake cleaner being used to find vacuum leaks. Does it work? I understand propane is preferred choice but regular carb cleaner also works.

 

[Chickmcgee]

The definitely works I use it all the time mostly in snowmobiles

 

[mechtech2]

Depends on the brake cleaner that is used.
Some don't burn.

 

[Chickmcgee]

I use Auto Zone Brake Cleaner