Having problems with your 2003 Audi A6 ?

2003 A6 Runs very rough have a hand held obd II diagnostic reader with a code po 431 warm up catalyst below threshold bank 2 is it just plugs ?

Posted / edited by AnonymousUser on : 01-06-2020

Answers :

No, it's either a clogged catalytic converter or, more likely, a bad secondary O2 sensor on the driver's side. The secondary sensor is the one after the catalytic converter, which is used to measure its efficiency. When that sensor fails, the computer can't judge how well the cat is working and often throws a code such as this. However, it should also throw a failed O2 sensor, sensor 2 bank 2, at the same time. You may have a bad cat, but if it comes down to replacing parts, I'd do the sensor first - it's about 15% of the price of a cat.

You could take the two secondary sensors and swap them - move the left side one to the right side and vice versa, clear the code, then scan the car again after running and see if the code comes back the same. If it does, your cat is bad. If it comes back reading a problem on bank 1, it's the sensor.
Repair Help & Product Troubleshooting for 2003 Audi A6

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