P0430: Catalyst Efficiency Below Threshold (Bank 2)
P0430 means the engine computer has decided the catalytic converter (the part that cleans exhaust gases) on bank 2 is not cleaning as well as it should. The car usually drives normally, but the check engine light stays on and the car can fail an emissions test.
You can drive, but get it checked soon
The car typically drives as usual and the code does not trigger limp mode. Still, the cause may be a misfire or rich running that can damage the catalyst further, and a broken-up catalyst can cause rattling or loss of power, so get it checked soon.
What it means
Bank 2 is the side of a V or boxer engine that does not hold cylinder 1. This code only applies to engines with a separate catalyst on each bank; engines with a shared catalyst on a Y-pipe report P0420 instead. The computer compares the signals of the oxygen sensors in front of and behind the bank 2 catalyst. A healthy catalyst smooths out the rear signal. If the rear signal moves too much like the front one, the computer sets P0430. The test only runs when the engine is warm, in closed loop (the computer adjusts fuel using sensor feedback) and without misfires, fuel faults or sensor faults. The reference notes that GM can set the code on the first trip when the ratio falls below 0.35, while Ford usually needs several trips.
Likely causes
- Catalyst aged or poisoned (oil consumption, silicone, coolant)Very likely
Wear or contamination from burned oil, silicone or coolant coats the catalyst and reduces its ability to clean exhaust.
- Catalyst overheated by misfire or rich runningPossible
Unburned fuel burning inside the catalyst can overheat and damage it.
- Rear oxygen sensor sluggish, dirty or unsuitablePossible
A slow or wrong sensor gives a signal that looks like a failing catalyst even when the catalyst is fine.
- Exhaust leak ahead of or at the rear sensorPossible
Extra air entering the exhaust distorts the sensor reading and can trigger the code.
What you may notice
- Check engine light on, with often no change in how the car drives
- Failed emissions test (higher HC, CO and NOx, meaning unburned fuel, carbon monoxide and nitrogen oxides)
- Rattling noise or loss of power if the catalyst has broken up
What to check, cheapest first
- 1Read the stored codes and look for misfire, fuel or oxygen sensor codes, including related ones like P0420, P0431, P0432, P0156 or P2272. Fix those first, since the test will not run properly with them present. · you can do it
- 2Listen and look for exhaust leaks near the bank 2 manifold, the pipe before the catalyst and the rear sensor (ticking, soot marks, hissing on cold start). · you can do it
- 3Check for signs of oil or coolant consumption, such as falling fluid levels or blue or white exhaust smoke, since these poison the catalyst. · you can do it
- 4View live data of the bank 2 front and rear oxygen sensors. A rear signal that swings like the front one points to a weak catalyst; a slow or flat rear sensor points to the sensor. · mechanic
- 5Confirm the rear oxygen sensor is the correct type and in good condition before replacing the catalyst. · mechanic
- 6If the catalyst is confirmed faulty, replace it, clear the code and complete a drive cycle (a set pattern of driving that lets the monitor run again) to confirm the fix. · mechanic
Related codes
Frequently asked questions
Can I keep driving with P0430?+
Usually yes for a short time, since the car normally drives as before. Have it checked soon, because misfire or rich running can damage the catalyst, and a broken catalyst can cause power loss.
Can a loose gas cap cause P0430?+
The reference lists no gas cap cause for this code. A loose cap is tied to evaporative system codes, so P0430 more likely points to the catalyst, rear sensor or an exhaust leak.
Will P0430 pass an emissions test?+
Unlikely. The check engine light is on and the code is emissions-relevant, so the car will typically fail until the problem is fixed and the monitor has run again.
What is the difference between P0430 and P0420?+
P0420 refers to bank 1 or to a shared catalyst, while P0430 refers to the separate bank 2 catalyst on V and boxer engines.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10