Catalytic Converter Problem? Please Help.

[j30]

Hi all, I have a problem and could use some help. My 2007 CX9 107K Touring was driving fine until one morning going to work it started losing power, rough sounding and died. After a few minutes of trying to get it going again it started and I was able to drive it a few miles to mechanic. Check engine light was flashing while driving to mechanic.

I was told that it was throwing 3 misfire codes, one badly cracked coil. They replaced sparkplugs again (done before at 77K) and the bad coil. Still not working good and throwing same codes. It fried the PCM (a TSB for this model that I didn't know about). They then replaced all the coils and PCM was repaired at an online place called circuitboardmedics.com at my request and was sent back to us. The car was running fine after this. I drove it 36 miles and next morning the check engine light came on. I went to Autozone and they read two codes P0420 and P0430 faulty cat converter/ exhaust leak. My mechanic came up with faulty cat converter, below normal flow through cat I was told. He cleared the codes and check engine light. The check engine light came on 17 miles later and is still on.

I have a problem believing this. I have never heard of any CX9 owner having problems with cat converter and wouldn't these codes have come up before or even during the coil/PCM breakdown?
Someone suggested that maybe the O2 sensors might have been messed up by the coil/PCM breakdown? Does this sound possible? Are there specific codes that would come up for faulty O2 sensors or would they throw up the faulty cat converter code? It is driving just fine. I would appreciate any help you could give. Thanks.

 

[BRIAN_MP5T]

NEVER DRIVE THE CAR WITH A FLASHING CHECK ENGINE LIGHT

Probably did some major damage to the engine.

 

[just_phil]

When a coil is not working properly, a misfire occurs. This causes un-burnt fuel to be dumped into the exhaust. Catalytic converter will overheat and get damaged over the time. Perhaps that's what you are seeing.

 

[J&J's Dad]

Yep, the coil failure probably sent unburnt fuel through a cylinder or two. There is an element in the factory 3 way catalytic convertor that can't handle much unburnt fuel. It would take a bit longer for the cat problem to manifest after the coil failure. That would be why the code didn't appear right away. Yes, there are seperate OBD2 codes for O2 sensor failures. The P0420 code could still be an O2 sensor instead of the cat itself, but that's less likely with the P0430 code also. Check for a significant exhaust leak before replacing the O2 sensors or cat though.