mmarton Posted October 27, 2014 Share Posted October 27, 2014 I had a check engine light come on and the codes showed, among other things that I needed a new catalytic converter and MAF sensor. Got that done by a shop but the CEL came back. I brought it back and the technician guessed that it was probably the air-fuel ratio sensor. Not being a mechanic, I never heard of it before. But why didn't the code reader isolate the air-fuel ratio sensor in the first place? The only other indicator was a code saying that the I was running "rich." Anyway, no more CELs. Link to comment Share on other sites More sharing options...
scontivt Posted October 27, 2014 Share Posted October 27, 2014 Take your car to someone who will actually diagnose the issue. Anyone can read a code, say it's a bad Cat and MAF, replace it and send you on your way. There are indicators within OBD-II, like A/F ratios and O2 sensor voltages, that tell someone whether or not the Cats were in fact bad, or if the Maf was bad, or etc... To quote quite a few members on this forum, cats don't fail that often on Subarus (unless you have a PZEV Legacy), and when they do, it is caused by an underlying issue (i.e. - Are you burning oil, are you running rich, are you misfiring, or do you have some other air/fuel issue). Good luck, I know chasing emission related codes suck. Steve Link to comment Share on other sites More sharing options...
mmarton Posted October 28, 2014 Author Share Posted October 28, 2014 Actually, I took the car to two shops, a Japanese car specialist and a local Subaru dealer. Both of them got the same codes, including the one for the MAF. Neither of them got any indication of the issue with the air-fuel ratio sensor. It was only after the MAF switch out didn't solve the problem that the AFR was guessed as the issue. No indicators. By the way, the dealer gave me a fully loaded 2015 Outback loaner. Very, very nice. Link to comment Share on other sites More sharing options...
Max Capacity Posted October 28, 2014 Share Posted October 28, 2014 Sometimes, when you get a fault, that item being bad will cause another fault. Say the MAF was bad, that could cause the car to think it wants more fuel. More fuel after a while can cause the front O2 sensor to read rich, that will cause it to throw a code. When you fix the first issue the second one should go away. It may take a few miles for the front O2 to clean up. 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
mmarton Posted October 28, 2014 Author Share Posted October 28, 2014 Thanks. The shop that diagnosed the AFR removed the new MAF, put the old one back in, and changed out the AFR. No more problems. Link to comment Share on other sites More sharing options...
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