P0430 on a Buick is "Catalyst System Low Efficiency, Bank 2." The engine computer has tested the catalytic converter on the second cylinder bank and found that it no longer stores enough oxygen. Only a Buick with two monitored exhaust banks can set it — the 3.6L V6 in the Enclave, LaCrosse and Regal GS, and the Northstar V8 in the Lucerne. GM's own 2008 OBD documentation shows the familiar 3800 V6 does not have a P0430, and four-cylinder Buicks never set it. Before anyone sells you a converter, GM's advice for older Buicks is to check something that costs nothing: the ignition coil ground on that bank.
Jump to a section: What P0430 means · Which Buicks can set it · Where bank 2 is · P0430 alone vs with P0420 · What GM has documented · Warranty · Symptoms · Causes and how to confirm each · How it's diagnosed · Parts and cost · GM documents · What other pages get wrong · FAQ
What Does P0430 Mean on a Buick?
Each bank of a Buick V6 has its own catalytic converter, an oxygen sensor ahead of it and one behind it. The engine control module (ECM) judges each converter by how much oxygen it can store — a worn converter lets the downstream sensor mirror the upstream one far too quickly.
GM's 2008 OBD documentation for the Enclave's 3.6L V6 (LY7) lists separate catalyst tests for bank 1 (P0420) and bank 2 (P0430). The test runs during a warm idle with the vehicle stopped and throttle closed. The ECM measures the response-time difference between the pre- and post-catalyst sensors, scales it between a "best failing" and "worst passing" converter from calibration tables, and produces a normalised ratio where 1 is a good converter and 0 a very bad one. The code sets when the filtered ratio falls below 0.35. It is a Type A code on that engine, so one failed test can light the check engine lamp.
GM blocks the test while misfire, fuel trim, oxygen sensor, MAF and many other codes are set. If P0430 shares the scan with any of those, they come first.
For the general GM picture, see our P0430 GM diagnosis guide.
Which Buicks Can Set P0430
We checked GM's OBD documentation and bulletins engine by engine:
- 3.6L V6 — GM's 2008 OBD documentation lists P0430 for the LY7 in both the Enclave group and the LaCrosse/Lucerne group. Later 3.6L engines (LLT, LFY, LGX) also have two monitored banks, as GM's bank 2 fuel trim documents for the Enclave and 2017 LaCrosse show.
- 4.6L Northstar V8 (Lucerne) — GM's 2008 OBD group covering this engine lists P0430.
- 3800 V6 (LaCrosse, Allure, Lucerne 3.8L) — GM's 2008 OBD documentation for the 3.8L (L26) lists P0420 only. On these Buicks a converter code is P0420.
- Four- and three-cylinder Buicks — Encore, Encore GX, Envista, Verano, Regal and Envision four-cylinders, LaCrosse 2.4L, Cascada: one bank, so P0420 only.
An older reference: GM bulletin 3679, which NHTSA indexes to the 2004–2006 Rendezvous and 2005–2006 LaCrosse, concerns DTC P0420 or P0430 — consistent with the 3.6L V6 those models offered. We have seen only the index entry, not the document.
Tools for checking the converter
FOXWELL NT614 Elite Scanner
$233.69Compare upstream and downstream O2 activity on bank 2.
FOXWELL NT726 Bidirectional Scanner
$368.99Bidirectional scanner for misfire counts and fuel trim history.
Compression Tester with Fuel/Vacuum Gauge
$25.65Vacuum gauge for spotting a restricted exhaust.
Where Bank 2 Is
GM numbers the 3.6L V6 so bank 1 contains cylinder 1 — the right bank viewed from the flywheel end. Bank 2 has cylinders 2, 4 and 6.
- Enclave, LaCrosse V6, Regal GS V6 (transverse): bank 1 is the rear bank, nearest the firewall. Bank 2 is the front bank, nearest the radiator, so the P0430 converter and its sensors are on the front side of the engine.
- Lucerne Northstar V8: confirm bank location in the service information for your VIN; we have not verified it from a GM document for this article.
Mixing up the banks is the most expensive mistake on this code. Confirm which sensors are bank 2 sensor 1 and bank 2 sensor 2 on your scan tool before you touch anything.
P0430 Alone vs With P0420
| What's stored | What it suggests | Where to look first |
|---|---|---|
| P0430 only | Something specific to the front bank | Bank 2 misfire history, bank 2 coil ground (PIP5232C), bank 2 injectors, exhaust leak on that side |
| P0420 and P0430 together | A cause both converters share, or simple age | Oil or coolant consumption, a long-running rich condition, high mileage, software level |
| P0430 with P0175 or P0174 in history | Bank 2 ran rich or lean for a long time | Fix the fuel trim cause before any converter |
What GM Has Documented
Check the coil ground for that bank
GM preliminary information PIP5232C (March 2016) covers 2016 and prior GM cars and gasoline trucks where the catalytic converter has come apart or set P0420 and/or P0430 with no apparent reason. NHTSA indexes it to a long list of Buicks, including the Enclave, LaCrosse, Lucerne, Rendezvous and Rainier. GM's recommendation is specific to the bank: inspect the ignition coil ground terminal on the engine block for the bank with the concern for a poor crimp, and check for corrosion or damage at the ring terminal, fasteners and grounding surface. If nothing is wrong, tighten the ground bolt to specification.
The reasoning: a weak ground gives weak or intermittent spark on that bank, unburned fuel ends up in that bank's converter, and the converter overheats. Fit a new converter without fixing the ground and the replacement is at risk too.
After an engine failure
GM bulletin 06-06-01-010D covers vehicles with close-coupled converters. If an engine fails — a broken valve or piston, or a severe overheat — converter debris or melted ceramic can be drawn into a replacement engine. GM tells technicians to inspect each converter during an engine replacement and replace any that are damaged. If your Buick's P0430 appeared after major engine work, that converter deserves a close look.
Software
The two GM software bulletins for P0420 on Buicks (19-NA-057 for the 2013–2015 Encore and 25-NA-005 for the 2024 Envision) apply to single-bank engines. We found no Buick software bulletin for P0430. A dealer can still confirm your ECM is at the latest calibration.
Warranty
Under the EPA's federal emissions warranty, catalytic converters are "specified major emission control components" covered for 8 years or 80,000 miles on 1995 and newer vehicles, for defects in materials or workmanship. Damage caused by misfire, oil burning or impact is treated differently, and some states set longer terms. On a newer Enclave, check the warranty booklet and ask the dealer before paying for a bank 2 converter.
Symptoms of P0430
- Check engine light, usually without a driveability change
- Failed emissions or inspection test
- Sulfur smell from the exhaust
- Rattle from the front-bank converter if the substrate has broken
- Power loss if the converter is restricted or melted
- Misfire codes on cylinders 2, 4 or 6, or bank 2 fuel trim codes, in history
Causes and How to Confirm Each
| Cause | How to confirm it | Notes |
|---|---|---|
| Bank 2 misfire damage | Misfire history and counters for cylinders 2, 4, 6 | The most common converter killer |
| Poor coil ground on bank 2 | Inspect crimp, corrosion and torque at the bank 2 coil ground (PIP5232C) | Free to check; fix before replacing the converter |
| Exhaust leak ahead of the bank 2 rear sensor | Inspect manifold, flange gaskets and joints; smoke test | Outside air skews the sensors |
| Long-running rich or lean bank 2 | P0175/P0174 history; current fuel trims | Fix trims first |
| Oil or coolant contamination | Oil consumption, coolant loss, plug fouling on bank 2 | Contaminants coat the catalyst |
| Bank 2 downstream O2 sensor fault | Sensor codes, slow or stuck signal | Less common than a real efficiency loss |
| Worn or debris-damaged converter | Rattle, restriction, history of engine failure (06-06-01-010D) | Replace only after the root cause is fixed |
O2 sensors and leak parts
Delphi ES20008 O2 Sensor (2006–2017)
$115.99Delphi O2 sensor for 2006–2017 Chevy, GMC and Cadillac. Confirm fitment by VIN before ordering.
GM Genuine 12657188 Heated O2 Sensor
$46.47GM Genuine heated O2 sensor 12657188. Confirm fitment by VIN before ordering.
MAHLE F32274 Exhaust Flange Gasket
$13.00MAHLE exhaust flange gasket — exhaust leaks can set P0430 on a good converter. Confirm fitment by VIN before ordering.
How Is P0430 Diagnosed?
- Confirm the engine has a bank 2. A four-cylinder or 3800 Buick should not set P0430.
- Read all codes and freeze frame, and fix misfire, fuel trim, O2 and MAF codes first.
- Identify bank 2 — the front bank on the transverse 3.6L — and its sensors on the scan tool.
- Review misfire history for cylinders 2, 4 and 6.
- Inspect the bank 2 coil ground per PIP5232C.
- Check for exhaust leaks on the front bank, up to the rear sensor.
- Compare both banks' sensors at warm idle. A good converter keeps its downstream signal much steadier than the upstream one; the bank 1 side gives you a built-in comparison.
- Check oil and coolant consumption if both converters look tired.
- Ask a dealer to check the VIN for bulletins, calibration level and emissions warranty.
- Clear codes and drive with some warm idle stops so GM's catalyst monitor can run.
Parts and Cost
| Repair | What it involves | Cost picture |
|---|---|---|
| Coil ground repair | Clean, re-crimp or torque the bank 2 ground | Minor |
| Ignition coil or spark plugs | Where bank 2 misfire is confirmed | Modest |
| Exhaust gasket or leak repair | Front bank flanges and joints | Minor to modest |
| Bank 2 downstream O2 sensor | Only if the sensor tests bad | Modest |
| Bank 2 catalytic converter | After the root cause is fixed; must meet the vehicle's emission certification | Large — check the 8-year/80,000-mile emissions warranty first |
Fix the cause first
Exhaust Manifold Gasket Set, 2010–2017 3.0L/3.6L
$10.99Exhaust manifold gasket set for 2010–2017 3.0L/3.6L V6s. Confirm fitment by VIN before ordering.
ACDelco 41-162 Iridium Spark Plugs (2)
$14.99ACDelco 41-162 iridium plugs — misfires kill converters. Confirm fitment by VIN before ordering.
95-Piece Mechanics Tool Set (Metric & SAE)
$99.99Mechanic tool set.
GM Documents Relevant to P0430 on Buick Models
We found no current GM bulletin that names P0430 for a specific Buick model with a model-specific repair. These are the most relevant GM documents we read or found.
| Document | Subject | Status |
|---|---|---|
| PIP5232C (Mar 2016) | Premature converter failure or P0420/P0430; inspect the coil ground for the bank with the concern | 2016 and prior GM cars and gas trucks, indexed to many Buicks — verified |
| 06-06-01-010D (Feb 2018) | Close-coupled converter inspection when replacing an engine | 2019 and prior GM vehicles — verified (does not name a DTC) |
| GM 2008 OBD documentation, groups 3, 10, 12a and 13 | P0430 catalyst test (OSC ratio below 0.35, Type A) for the 3.6L LY7 and 4.6L Northstar; 3.8L L26 lists P0420 only | 2008 Enclave, LaCrosse, Lucerne, Allure — verified |
| Bulletin 3679 (older GM service document) | Service information on DTC P0420 or P0430 | 2004–2006 Rendezvous, 2005–2006 LaCrosse — corroborated (NHTSA index entry only) |
Have a dealer check your VIN against current bulletins and emissions coverage rather than relying on any article, including this one. The check is free.
What Other P0430 Pages Get Wrong
- Listing P0430 for the 3800 V6 or four-cylinder Buicks. GM's documentation shows only P0420 on those engines.
- Putting bank 2 at the firewall on an Enclave. On the transverse 3.6L, bank 2 is the front bank.
- Replacing the converter first. GM's PIP5232C says to check the coil ground for that bank; misfire and fuel trim faults come first.
- Swapping the rear O2 sensor as a fix. A sensor reporting a weak converter is usually right.
- Replacing both converters for a single-bank code. P0430 alone points at bank 2.
- Forgetting the emissions warranty. Catalytic converters are covered for 8 years or 80,000 miles against defects under federal rules.
Frequently Asked Questions
Which catalytic converter is bank 2 on a Buick Enclave?
The one on the front bank, nearest the radiator — the side with cylinders 2, 4 and 6.
Can my 3.8L Buick LaCrosse set P0430?
According to GM's 2008 OBD documentation for the 3800 V6, no. That engine reports converter efficiency through P0420 only.
Do I need to replace both converters for P0430?
Not normally. P0430 is about bank 2. If P0420 is also set, look for a shared cause such as oil consumption before replacing anything.
Is P0430 covered under warranty?
Catalytic converters fall under the federal 8-year/80,000-mile emissions warranty for defects in materials or workmanship. A dealer can confirm coverage for your VIN.
Can I drive with P0430?
Usually yes in the short term if the engine runs normally, but it will fail an emissions test. A flashing check engine light means misfire — stop driving, because that can destroy the converter.
Why did P0430 come back after a new converter?
The root cause was probably still there — a bank 2 misfire, a rich condition, oil burning, or the coil ground issue GM describes in PIP5232C.
Shop Related Parts & Tools
Confirm the code is bank 2, fix any misfire or fuel trim faults, and check the bank 2 coil ground and emissions warranty before buying exhaust parts; order parts by VIN.
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FOXWELL NT301 OBD2 Scanner — shows bank 1 and bank 2 oxygen sensor data side by side, a built-in comparison for judging the bank 2 converter.
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MAHLE Catalytic Converter Gasket F32898 (Buick, Chevy, GMC) — for sealing an exhaust leak at a converter flange on the front bank; confirm fitment against your VIN.
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ACDelco Oxygen Sensor 12701634 (Buick, Chevrolet, GMC) — a GM oxygen sensor for when the bank 2 rear sensor itself tests bad; confirm fitment and sensor position against your VIN.
Related Guides
- P0430 GM Diagnosis Guide — general GM background
- P0420 on a Buick — the bank 1 converter
- P0175 on a Buick — a rich bank 2 can kill its converter
- P0300 on a Buick — misfire diagnosis
- GM Exhaust Manifold Cracking and Ticking