Error code P0421?

[The Glademister]

I'm getting check engine light and my Durametric shows - P0421 Bank one catalyst warm-up efficiency below threshold. I'll clear it but it will come back after 20-30 miles. What's the prognosis doctor? Oh, this is on my '07 Cayman S with 58,000 miles.

[paulv]

Here's some info to start with:

Possible fault causes
1) Oxygen sensors in front of and behind catalytic converter swapped (position in exhaust assembly)
2) Valve lift error
3) Aged oxygen sensor behind catalytic converter
4) Catalytic converter faulty (pre-catalytic conversion rate too low)

Doubt that item #1 is the cause unless someone was doing work on the car.

For item #3, try moving the Bank 1 sensor to Bank 2 and see if the fault also moves -- if it does, then the aft bank 1 sensor is defective. Also check wiring as these sensors are low to the ground.

Regards,
paul...

[The Glademister]

Originally Posted by paulv

Here's some info to start with:

Possible fault causes
1) Oxygen sensors in front of and behind catalytic converter swapped (position in exhaust assembly)
2) Valve lift error
3) Aged oxygen sensor behind catalytic converter
4) Catalytic converter faulty (pre-catalytic conversion rate too low)

Doubt that item #1 is the cause unless someone was doing work on the car.

For item #3, try moving the Bank 1 sensor to Bank 2 and see if the fault also moves -- if it does, then the aft bank 1 sensor is defective. Also check wiring as these sensors are low to the ground.

Regards,
paul...

Thanks Paul. The whole "catalytic" term had me a little confused. I heard on another forum the cats and maybe the O2 sensors are covered under 8 year emission warranty. Going to give the dealer a call...

[The Glademister]

Originally Posted by The Glademister

Thanks Paul. The whole "catalytic" term had me a little confused. I heard on another forum the cats and maybe the O2 sensors are covered under 8 year emission warranty. Going to give the dealer a call...

That's what I figured. Cats only covered. I'll be swopping the bank 1 and bank 2 O2 sensors.

[paulv]

Typically, it's the cats, the DME (PCM) and the PCM connector under the dash. The catch with the cats is that (as the old saying goes) cats don't commit suicide, they're murdered!! Which means they fail due to owner's foul ups!

Regards,
paul...

[The Glademister]

Update - I swopped the two post-cat O2 sensors and it hasn't thrown a code yet.

[Muzzy]

I have exactly the same problem and had all 4 sensors replaced. Everything was fine until about a month went past and the error code came back. It now comes back on every day or so. Also, I can sometimes hear a metal shaking sound when I rev the car slightly harder.

I'm starting to think I have a cat that is going bad...??

[Wayne 962]

Yup, the two oxygen sensors measure the efficiency and proper operation of the catalytic converters. Many times when they throw a code, it's the sensors themselves that have a problem. But in this case, if you hear rattling, I would suspect that the problem lies with the converter and the 02 sensors are giving you an accurate warning.

-Wayne