Hi, I have a 2005 XC70 with a check engine light that goes on and off. I had the codes read and had aP0101 MAF code so replaced the MAF. The light went off for a short time (maybe 50 miles?) then back on.

Months before all of this the car didn't start and the mechanic had to replace the fuel pump (new) and fuel filter (new) and a fuel pump module (used). After I picked the car up the fuel was leaking so the mechanic tighten something (I guess) and it no longer leaked so I figured that was all set. I mention this because now I think the check engine light may be connected to something with the fuel system because when I fill up the tank the light goes on for about 50 miles then goes off. The gas cap looks OK - no cracks, etc.

The codes still read P0101. The last time I had them read they had to plug it in 3 times to get a reading. A side note, the gas gauge no longer works so I just fill up the tank every 200 miles. ANd for awhile the radio went on the fritz not allowing a station change until by chance we washed the car and really sprayed out the wheel wells on the driver's side and a ton of mud came out. Suddenly the radio worked fine. I mention this because I wonder if it's an electrical problem in general

Also, about 4 years ago I had to replace the ABS module(used) and the ECM (new).


Any thoughts on this problem would be appreciated. I love this car and want to keep it if I can. Thanks

 

the P0101 is telling you the MAF is "out of range" meaning it can't compensate ehough for the fuel trim. Usual suspects here are vacuum leaks and a dirty or faulty MAF sensor. As you noted you replaced the MAF, the caution there is whether an OEM sensor was used or aftermarket. If you went aftermarket you may want to try and get an OEM MAF (say a used one out of a yard car) swap out, clear codes and hope. Since this is a fuel trim code, you may also want to see if you can reset the fuel trim stored in the ECU by clearing the codes and disconnecting the battery for about an hour or two as not all code readers also reset the fuel trim baseline. If those tricks dont work, I'd ask the shop for a smoke test to look for a more obscure vacuum/intake leak.

 

Sounds to me like you have a vacuum leak.

Since this is a turbo engine, you will have to check all of the turbo lines since any air that escapes from the boost side will also confuse the computer.

The most likely culprit is the soft hose at the top of the turbo output connection and the associated soft hose at the other end of that pipe entering the intercooler.