My Max threw a code last night...P1273= "AF sensor lean shift detected". My car is 04 SL 4at, with Fujita CAI, cattmant y-pipe (-cat), and Magna Flow mufflers. The code states 1 of 3 things.. 1)failed AF sensor 2)vacumm leak 3)Fuel injector or pressure regulator fault. I had the y-pipe on for approx. 3 weeks with no codes. The engine seems strong and no bogging or missing. There does seem to be a faint sound from underneith the car when deaccelerating kinda sounds like a flat tire sound. Could there be a leak in the exhaust that would throw the code? Any help would be awesome...Also the car has 50,000 miles and is under the power train warranty not sure if the CAI and exhaust would nulify the warranty or even if the AF sensor is part of the powertrain? Thanks in advance..

 

The hissing sound is most likely from the Cattman y-pipe...when did you purchase the y-pipe? I know that the first batch had different flex-pipes than the ones they are producing now, which caused the hissing sound while the revs were going down around 3,000 RPM.

 

I bought the catmann 4 weeks ago.. post hissing issue.. The noise is not a hiss more of a whop,whop, whop.. sound. I know that is not the best description but I dont know really how to explain it.

 

I would double check the exhaust for leaks, if there is a leak thats the nosie you could be hearing. Also check the intake and make sure it's sealed up tight make sure you are not pulling in air after the MAF.

 

i also hear the hissing sound... i only hav a Fujita CAI installed... i gotta check it out again to see if its loose or not...