P0420 (Bank 1) vs. P0430 (Bank 2)
These codes are nearly identical, but point to different sides of your engine.
What is an Engine "Bank"?
An engine bank is a row of cylinders. Inline engines (I4, I6) have only one bank. V-type engines (V6, V8, V10) have two banks.
- Bank 1 is ALWAYS the side of the engine that contains Cylinder #1.
- Bank 2 is the opposite bank.
Finding Bank 1 can sometimes be tricky. A general rule for US-market cars is that it's the bank closer to the firewall, but always check your vehicle's service manual for confirmation.
Code Comparison
| Feature | P0420 | P0430 |
|---|---|---|
| Full Name | Catalyst System Efficiency Below Threshold (Bank 1) | Catalyst System Efficiency Below Threshold (Bank 2) |
| Affected Area | The catalytic converter on Bank 1 | The catalytic converter on Bank 2 |
| Common Engines | All engine types (I4, V6, V8) | Only V-type engines (V6, V8, etc.) |
| Diagnosis | Identical diagnostic process, just focused on Bank 1 components (O2 sensors, exhaust manifold). | Identical diagnostic process, just focused on Bank 2 components. |