P0430 Code: Catalyst Efficiency Below Threshold (Bank 2)

What does P0430 mean?

P0430 stands for "Catalyst System Efficiency Below Threshold (Bank 2)" ^[1]. It is the same test as P0420, run on the other side of the engine. Your powertrain control module (PCM) compares the oxygen sensor in front of the converter with the sensor behind it. When the rear signal starts to look too much like the front one, the PCM decides the converter has lost efficiency and turns on the check engine light ^[2].

A V6 or V8 has two rows of cylinders. Bank 1 is the side with cylinder 1. Bank 2 is the other side. Each bank usually has its own converter and its own pair of oxygen sensors, which is why a V engine can set one code without the other.

Which side is Bank 2 depends on the engine, so never assume. Honda, for example, labels P0430 as the "front bank" on some V6 models in a 2021 warranty notice ^[3]. Check the service information for your engine before you buy a sensor or a converter.

Is it safe to drive with P0430?

Yes, P0430 is usually safe to drive in the short term. Most drivers notice nothing but the light, because the converter test does not change how the engine runs. Some code libraries list a slight loss of power, a sulfur smell or lower fuel economy as possible signs ^[1]. Those point to a converter that is further gone, so do not put the visit off.

The exception is a misfire. If the check engine light starts flashing, or the engine shakes badly, pull over and stop driving. A flashing light means unburned fuel is reaching the converter, where it can overheat and destroy it. Our guide to a flashing check engine light explains what to do next, and P0300 covers misfire codes.

The light also matters for registration. California's Bureau of Automotive Repair says a vehicle will not pass a Smog Check with the check engine light on ^[4].

What causes P0430?

The usual causes, most common first:

1. Worn or damaged Bank 2 catalytic converter.
2. Faulty Bank 2 downstream oxygen sensor. A slow rear sensor can make a good converter fail the test.
3. Exhaust leak before or between the Bank 2 sensors. A cracked manifold or a leaking gasket lets air in and confuses the readings.
4. Long-term rich or lean running, or misfires, which overheat or coat the converter.
5. An engine burning oil or coolant.

Carista lists the same group of causes for P0430 ^[1]. Identifix adds leaking injectors, high fuel pressure, wrong fuel, a bad coolant temperature sensor or thermostat, and outdated PCM software to the list for catalyst efficiency codes ^[2]. A lean code on the same side, P0174, is a strong hint that a vacuum or fuel problem is involved.

What does it mean when P0420 and P0430 appear together?

This is the most useful clue a V engine gives you. When both banks fail the converter test at once, look for a cause the two sides share before blaming two converters. Something that affects only one side, like a leaking gasket or a bad sensor, rarely sets both codes.

Software is a real possibility. Ford has issued bulletins for P0420 and P0430 set by PCM calibration on certain trucks, including 2022 to 2023 F-150 trucks with the 3.5L PowerBoost hybrid engine ^[5]. Honda extended warranty coverage on some 2016 to 2018 V6 models for the same pair of codes ^[3]. See P0430 on Ford and P0420 on Honda.

How do you diagnose P0430?

Work from the cheapest checks up. A scanner that shows live data and freeze frame is enough for the first steps; see how to use an OBD2 scanner, and use our code lookup for any other codes.

1. Read every code and save the freeze frame. Misfire and fuel trim codes come first.
2. Compare the banks in live data. Look at short and long term fuel trims for each bank, and watch both rear oxygen sensors on a warm engine. A Bank 2 rear sensor that switches like its front sensor, while Bank 1 stays steady, points to the Bank 2 converter ^[2].
3. Inspect the Bank 2 exhaust for leaks with the engine cold: soot marks, broken studs and ticking at startup.
4. Have the rear sensor tested. A technician confirms it responds to forced rich and lean conditions.
5. Ask a dealer to check your VIN for software updates, bulletins and open recalls.
6. Confirm the converter with temperature and back pressure checks before replacing it.

The big advantage of a V engine is that you have a built-in comparison. Bank 1 and Bank 2 see the same fuel, the same driving and the same software. If Bank 1's rear sensor stays calm and Bank 2's rear sensor busily switches, the difference is on the Bank 2 side. If both rear sensors look busy, the cause is more likely something the whole engine shares. Write down the freeze frame values before anyone clears the code, because they show the engine speed, load, temperature and fuel trims at the moment P0430 set.

Steps 1 to 3 are fair driveway checks with a basic scanner and a flashlight. Leave work under a hot or running vehicle, and anything on a lift, to a qualified technician. Exhaust parts stay hot long after the engine is shut off.

How do you fix P0430, and what does it cost?

The repair matches the finding: a gasket, a sensor, a misfire fix, a software update or a converter. Replacing the Bank 2 converter without fixing what damaged it often brings P0430 back. If a misfire or an oil burning problem ruined the old converter, the new one faces the same conditions. As of November 2026, Identifix cites RepairPal averages of $454 to $550 for an oxygen sensor replacement and $2,301 to $2,473 for a catalytic converter replacement ^[2]. What moves your bill: whether the converter is a separate pipe section or built into the exhaust manifold, how much has to come apart to reach the Bank 2 side, labor rates in your area, and whether your state requires a specific type of replacement converter. Ask the shop to show you the test results that justify a converter before you approve one.

Before paying, check coverage. Federal rules set an 8-year or 80,000-mile warranty period for catalytic converters on light-duty vehicles and trucks ^[6].

After the repair, clearing the code only turns the light off. It does not fix anything, and inspection stations check that the readiness monitors have finished their self tests. California's BAR suggests driving a week or two after repairs so the monitors can reset ^[4]. Removing or disabling emissions equipment is never an option: tampering with a vehicle's emissions controls is illegal under the Clean Air Act ^[7].