Hello, a week ago, the check engine light on my car is on, so I use the OBD to test it, and then I erase the code to see if it come back again.

After a week, the check engine light come back again, and here's the code that I have after using the OBD II to scan it.

P0421
Warm Up Catalyst Efficiency Below Threshold (Bank 1)

What does this mean, and how do I fix this problem?

 

probably the worst code mate the catalyst is on its way out

 

cat going bad is a possibility but that would be worst case scenario.

could be something simple like 02 sensor or MAF

if you have a Bentley and know someone with a VAG COM you could narrow the problem down

 

That's what I thought too.

It's either the cat converter or the o2 senor, which is not that bad, because they're pretty cheap to replace.

Where do you find o2 sensor for a 02 audi, a4, quarttro 3.0, v6?

 

P0421
16805
Primary catalytic converter, bank 1,

Not effective enough 1)
- Generate readiness code Page 01-82 . If the same malfunction is indicated again, replace primary catalytic converter, bank 1.
Repair Manual, Engine Mechanical, Repair Group 26; Exhaust system components, removing and installing

 

yep that's what I would do the o2 sensors have their own codes and there are 4 o2 sensors and 2 catalyists, the primary one is to your left if standing looking at the car from the front ie: number 1 cylinder side