I went the same route, but luckily I had it done in small town muffle shop so they only charged me $100 for labor to remove and install the Y-Pipe. The tech said "it wasn't fun." I had it priced for replacement in the city at a mechanic shop, and they quoted $1400 for new y-pipe and labor ($95/hr).

The muffle shop charged me $450 to get the aftermarket Y-pipe replacement out of Houston. Total it ran me $590 including $40 for diagnostic. The diagnostic said it was bank 2 that was bad, which was the driver's side. Had it been the passenger side bank, the muffle shop said they could have easily cut out the bad cat and welded in a universal cat. The code is clear, and did not have to replace any O2 sensors either so based on my experience, if you get P0431, it is a cat problem and not an O2 sensor that the auto parts will try to sell you.

 

Raf6095, how many miles since your aftermarket cat replacement? Any issues? I'm curious since I'm going to be heading in the replacement direction - my code is back

 

If you don't want to pay for a new catalytic converter and just want the check engine light (CEL) to stay off I wonder whether you could fool the computer by replacing the oxygen sensor after the catalytic converter with some simple electronic circuit. My oxygen sensors put out a voltage of between 0.1 and 0.85 volts. What if you connected a battery and resistor circuit that produces say 0.5 volts to the oxygen sensor wires. It would be worth a try! My OBD2 iPhone app tells me the O2 sensor voltages. See my separate post.

 

HunterD, so far so good, I've driven about 350 miles with no issues. I'll update if something happens.

 

No need for any electric work. The cheap way to bypass this code is to space out both of the post cat oxygen sensors. The codes are due to the rear sensors indicating to the ECU that the readings are too dirty. By spacing them out of the exhaust stream a bit, the signal is cleaner, code is gone. Total cost: $8-$20.

 

The O2 sensors detect amount of oxygen left in the exhaust stream after catalytic converter. If all works well, all oxygen should be used up by the cat in converting pollutants to harmless gases. The sensors are very sensitive and update PCM many times per second (that is how the computer knows how much fuel to add to the engine for required load). I can't imagine that spacing them out would do much - it does not change amount of oxygen in the stream, therefore will not change the readings or behavior of the sensor.

As far as electronic "fooling" device - it has to be pretty complicated. There is a PCM check to see if O2 is present and working. When you idle the engine - a certain reading form rear O2 sensors is expected. Additionally when you rev the engine some oxygen does get past the cat converter since you are running lots of air through the system. All these fluctuations are expected by PCM at different running parameters. Just a simple resistor keeping 0.2 volt will not work.

There is a third option for keeping the Check Engine Light off - black tape.
I'm personally not a fan of that option, but i hear it works...

 

I know you put great thought into the last post but the anti-foulers work. It's been used for years by tuners and guys running aftermarket, free flow cats. It takes the rear sensors out of the direct exhaust flow, not just spaced back a bit.
I did this rather than dropping $1K or more on two Monteros now and it works great. But if you don't believe me, that's fine but for less than $20 I think you might want to give it a shot.

 

Perhaps you are right on the spacers. I can't really say since i have no experience with them. I'll do some researching and check it out. The reason I'm interested in all this is I got a cat converter that is going bad (old age). I live in the area where I'm not required do do emission tests, but I don't want to drive around with the CEL on all the time. If i can get away with some way to make the CEL stay off - it is a good deal. I'll be much happier this way than dumping $900 on the Y-pipe. I appreciate your feedback. That's what I love about this forum - lots of knowledge to go around.

 

Hunter D, Sorry for the delay in replying to your inquiry regarding where I purchased my OEM Y-Cat. I purchased it online at www.discountmitsubishi parts.com . They seem to be affiliated with Courtesy Mitsubishi in Attleboro, Massachusetts. Good Luck with your repair.

 

VKR, thanks for the info.