Exhaust and catalyst
P0430Catalytic converter efficiency below threshold, bank 2
Catalyst System Efficiency Below Threshold Bank 2
Get it diagnosed soon
Generic OBD-II code
Catalytic Converter
What this part does
Uses a catalyst bed to convert exhaust pollutants (CO, HC, NOx) into less harmful gases; efficiency is monitored by comparing upstream/downstream oxygen sensor activity.
What the computer is measuring
P0430 is the same test as P0420, run on the other cylinder bank. The computer compares the oxygen sensor ahead of the bank 2 converter with the one behind it, and decides the converter has stopped storing and releasing oxygen the way a healthy one does.
Bank 2 only exists on an engine with two cylinder heads: a V6, a V8, or a flat engine. Bank 1 is always the side containing cylinder number one, and which physical side that is depends entirely on the make. On many transverse V6 engines bank 1 is the rear bank against the firewall and bank 2 is the one you can see. On plenty of others it is the reverse. Look it up for your specific engine before you buy a part or condemn a sensor.
The useful thing about a bank 2 code is that the vehicle carries its own control group. If bank 1 passes and bank 2 fails, you have two nominally identical systems on the same engine, the same fuel and the same drive cycles, with one difference between them. Comparing the two rear sensor traces directly is faster and more conclusive than any single reading.
What you will notice
- Steady check engine light, no change in how the car drives.
- Often found only at an emissions test.
- Sometimes stored alongside P0420 when both converters are worn.
Likely causes, most common first
Ordered by how often each one actually turns out to be the problem, not alphabetically and not by part price.
A worn out catalytic converter on bank 2
Common on high mileage V6 and V8 engines. As with bank 1, the converter is usually the victim rather than the culprit.
A lazy downstream oxygen sensor on bank 2
The rear sensor is the only witness. Compare its behaviour against the bank 1 rear sensor, which gives you a free known good reference on the same vehicle.
An exhaust leak on the bank 2 pipe
Rear banks are often the harder side to reach and the side that gets a rusted flange or a cracked flex pipe first.
A misfire confined to bank 2
A single dead cylinder on that bank dumps unburnt fuel into that converter only, which is exactly why one side fails and the other does not.
What to check, in order
Confirm which bank is which before you touch anything.
Bank 1 contains cylinder number one. Bank 2 is the other side. Getting this backwards is the most expensive mistake on this code, because the two converters are often different parts.
Compare the bank 1 and bank 2 rear oxygen sensor traces side by side at a steady 2000 rpm.
If bank 1 is flat and bank 2 mirrors its front sensor, the difference is real and it is on bank 2. If both banks look the same, suspect the sensor or a shared cause rather than one converter.
Check for cylinder specific misfire counts on the bank 2 cylinders.
A misfire on that bank explains the code and must be repaired first. No misfire, and the converter or its sensor is back in the frame.
Inspect the bank 2 exhaust from the manifold to the rear sensor for leaks.
A leak found here explains the code without any converter fault at all.
Where this one turns up most
- V6 and V8 engines where one bank runs hotter or is harder to service than the other.
Codes that often show up alongside it
What a DriveDecode adapter can read
A DriveDecode adapter reads engine and emissions systems: the powertrain and emissions codes the OBD-II standard requires on every US vehicle it covers. It does not read ABS, airbag (SRS), TPMS or transmission-specific manufacturer codes. Those need make-specific decoding that generic OBD-II hardware cannot do.
Reading P0430 on your own car
DriveDecode pulls P0430 straight off the vehicle along with the freeze frame the computer stored when it set: the coolant temperature, engine load and speed at that exact moment. That context is what separates a fault that happens on a cold start from one that happens under load, and it is the first thing the list above asks you to narrow down.
Last reviewed 2026-09-05. Definition sourced from the published standard.