lzvzlm

I began receiving trouble code P0139 Monday after driving around in the heat for awhile running errands on my day off. From what I can tell this points to an issue with either the 02 sensor or the catalytic converter. I should have a day off sunday/monday and be able to lift the car and pull the catalytic converter down and shake it and look for the mesh to see if the cat is toast. I have noticed higher temps than usual with my OBD2 software, sometimes as high as 215 if I push it pretty hard and stay in a high gear but it doesn't appear to have any issues cooling to 180-190. I haven't driven it hard yet to look for a glowing cat at night. I dont have any symptoms really, maybe poor gas mileage. Seems like I am getting on average 12-13 MPG.

A couple questions before I begin this work.

1. How long of a drive, and how hard should I drive it to sufficiently be able to heat up the cat enough to visually spot a failure?
2. I was planning on eventually switching over to a BHR midpipe. When you switch to a BHR midpipe, are you required to have a functioning 02 sensor? It might be more cost effective and better for my car to just go ahead and get the BHR midpipe as opposed to possibly wasting my money on an 02 sensor that may not fix my issue. But if Ill need an 02 sensor with the BHR midpipe, might as well just order one and have it in transit and try that first.
3. Im not the most mechanically inclined. I can do a lot of work myself it just takes me longer than others. Im good at following directions. Something I am slightly concerned with when ive looked at the process of removing the catalytic converter is it seems theres a seal either on the front or rear that can go bad just from removing and checking the cat. Is there any real precautions I should take when beginning this work?
4. Seems like cobbport tune is needed to remove decat CEL codes unless I am looking at old threads, is an OBD2 device enough to just at least ignore the codes? They aren't actually throwing a check engine light or any warning on my dash, im only seeing these warnings in ultragauge.
5. I work 12 hour shifts, i realistically cannot work on it until saturday or sunday as I am working many extra hours. My plan is to monitor engine temps until then, any hidden dangers to waiting?

Thank you,
Michael

TeamRX8

iTrader: (25)

that code is most often the sensor, but never the cat converter

not to say whether your cat is good or bad, the code is not relative to it


Possible causes:
• Purge solenoid valve malfunction
• Looseness of rear HO2S
• Leakage exhaust gas
• Rear HO2S malfunction
• Fuel line pressure malfunction
• Leakage fuel
• Fuel pump unit malfunction
• AIR system malfunction
• Leakage engine coolant
• PCM malfunction

.

lzvzlm

So a bad catalytic converter wouldn't throw this code? When i used the site search feature it seemed like that was suggested by many users.

Thats a lot of potential issues, where would I start on this list? A few weeks ago I recieved p0661 but it dissapeared and hasn't come back. Any connection?

TeamRX8

iTrader: (25)

1 + 1 = 3 is pretty much par for the course around here.

Loki

iTrader: (1)

What that code is telling you is that the O2 sensor is not responding properly to changes in mixture. There aren't too many ways that can happen, the sensor is probably kaput. This is how O2 sensors die, if the heater doesn't burn out first.

That said, exactly as Team pointed out, that doesn't mean it's only the sensor. Checking the cat when it gets to 80-100k is never a bad idea. If would do that as a next step. If it's only the sensor, you can drive without trouble. If the cat is bad you want to know that sooner than later. The poor gas mileage is a warning sign, it should not be that low on a good car with good ignition and a good cat, driven appropriately.

Most midpipes will still have a bung for your O2 sensor, but if the pipe is catless, it will throw a code for the missing cat.

You can clear the code and see if it comes back.
I would not recommend testing your cat by getting it to glow. Not glowing doesn't mean it's fine, and glowing means it's definitely not fine and you are damaging your engine. Do it properly, inspect it.

The front midpipe seal can be damaged by undoing the joint but it's not expensive at Mazda if you do need to replace it. Don't use substitutes like foil paper, they will burn out in short order.