P0430 Code: Catalyst Efficiency Below Threshold (Bank 2), and How It Differs From P0420
Reviewed 2026-10-03. Checked against the sources listed below. This is general information, not a substitute for a mechanic's inspection.
Quick answer
P0430 is the same test as P0420, done on the other side of the engine. It only appears on engines with two cylinder banks, such as a V6 or V8. It means the catalytic converter on bank 2 (the side without cylinder number 1) is not storing oxygen well enough, according to its oxygen sensors.
P0420 vs P0430 at a glance
| P0420 | P0430 | |
|---|---|---|
| Which converter | Bank 1 (side with cylinder 1) | Bank 2 (opposite side) |
| Engines | Any engine | V6, V8 and other two-bank engines |
| Sensors compared | Bank 1 upstream and downstream | Bank 2 upstream and downstream |
| Common causes | Worn converter, leak, sensor, misfire | The same, on the other side |
Why only one side can fail
Each bank has its own exhaust path, converter and sensors on a two-bank engine. If one side has a misfiring cylinder, a leaking manifold gasket or a lazy sensor, only that side's converter test fails. So P0430 alone suggests a problem on bank 2 specifically, while P0420 and P0430 together suggest something affecting the whole engine, such as oil burning, a fuel trim problem or simply high mileage on both converters.
What to check before buying a converter
- Misfire codes on bank 2 cylinders. Fix misfires first. Unburned fuel overheats converters.
- Exhaust leaks on the bank 2 side, especially at the manifold, the converter flanges and in front of the downstream sensor.
- The bank 2 downstream sensor and wiring. Heat and road debris damage connectors.
- Both codes present? Then look for whole-engine causes before replacing parts on one side.
- Which side is bank 2 on your vehicle. It depends on the engine design, so confirm it in a service manual or with a parts store before ordering. Our guide on bank 1 vs bank 2 explains how to tell.
Replacing converters on a two-bank engine
Many trucks and SUVs, including the Toyota Tundra 5.7L V8 and the 4.0L V6 in the 4Runner, Tacoma and FJ Cruiser, use a converter on each side. Some shops replace both at once when both codes are present or mileage is high, so the two sides age evenly. If only P0430 is set and bank 1 tests fine, replacing just the bank 2 converter can be enough. Your shop can confirm with live sensor data.
Related AFECO parts
These converter sets are listed for the exact vehicles shown on each page. Confirm year, model and engine before ordering.
