P0430: your bank 2 catalytic converter tested weak

What the computer saw

Engines with two rows of cylinders, such as most V6 and V8 engines, have two banks, and often a catalytic converter for each. Bank 1 is the side with cylinder 1; bank 2 is the other side. The computer compares the oxygen sensor before the bank 2 converter with the one after it. When the rear one starts to look like the front one, the converter is not storing and cleaning the exhaust as it should, and P0430 is set. It means the test failed. It does not prove the converter itself is the broken part.

Likely causes, most common first

1. A worn bank 2 catalytic converter. The most common cause on older, high-mileage cars. Converters lose their ability to store oxygen over time.
2. A faulty bank 2 rear oxygen sensor. The rear sensor is the judge. If it reads wrong, a good converter can fail the test.
3. An exhaust leak before the bank 2 rear sensor. Outside air drawn in through a leak upsets the reading.
4. An engine problem on bank 2 that harmed the converter. Misfires on that side, burning oil or a rich mixture send unburned fuel and oil into the converter and wear it out early. Fix these first, or a new converter can fail the same way.

What you can note yourself

• Read every stored code, not just this one. P0420 with it means both converters tested weak; a misfire code on a bank 2 cylinder changes what P0430 means.
• Note whether the light came on after a recent repair, a long trip or a tank of fuel from a new station.
• Note any rattle from under the car or a smell of rotten eggs, and tell the shop.

What to tell the shop

• All the codes, including any pending ones.
• Ask whether they checked the bank 2 oxygen sensor readings and looked for exhaust leaks before quoting a converter.
• Any recent work on the engine or exhaust.

This page gives no verdict on whether a car is safe to drive; a mechanic can.

Questions people ask next

Is P0430 the same as P0420?

It is the same test on the other side of the engine. P0420 is bank 1, the side with cylinder 1; P0430 is bank 2. An engine with one row of cylinders has no bank 2 and cannot set P0430.

Why would only one converter test weak?

Each converter is judged on its own. One side can wear faster after misfires, an oil leak or a sensor fault on that side, so a single code is common.

Which side of the engine is bank 2?

Bank 2 is the row of cylinders that does not hold cylinder 1. Which side that is depends on the engine; the repair manual or the shop can show it.

Related pages

• P0420: the same test on bank 1
• P0420 and P0430 together: both converters tested weak
• P0420 came back after a new catalytic converter