P0175 Code on a Buick: Fuel Trim System Rich, Bank 2 (Buick Guide)

P0175 on a Buick is "Fuel Trim System Rich, Bank 2." The engine computer has been removing fuel from bank 2 for so long that it has hit its correction limit, and that side is still running rich. It can only appear on a Buick with two separately monitored cylinder banks — in practice the 3.6L V6 in the Enclave, LaCrosse and Regal GS, and the Northstar V8 in the Lucerne. The surprise for many owners: the classic 3800 V6 in the LaCrosse, Allure and Lucerne does not set P0175 at all, according to GM's own OBD documentation, and the injector bulletin most often quoted for P0175 does not list Buick.

What Does P0175 Mean on a Buick?

Your Buick's engine control module (ECM) trims fuel separately for each bank of a V6 or V8, using the upstream oxygen sensor on each side. Short-term trim is the instant correction; long-term trim is the learned one. Negative trim means fuel is being removed.

P0175 sets when bank 2's long-term trim stays at its rich limit. GM's OBD documentation for the 2008 Enclave's 3.6L V6 (RPO LY7) is a good illustration of how carefully GM tests before it blames the engine:

• The passive test fails when the weighted average of long-term trim with purge off falls below a factor of 0.755 — roughly 24% less fuel than base.
• If a passive decision can't be made, an intrusive test ramps EVAP purge off and requires the trims to stay rich across three test segments before the code fails.
• The test won't run with misfire, upstream O2 sensor, EVAP, injector, ethanol-composition, MAF, MAP, throttle or EGR codes present. It is a Type B code — usually two failing trips before the light comes on.

So a P0175 that survives GM's own purge-off test points at the engine itself rather than canister vapor. Thresholds differ between engines and years; the 2008 LY7 figures are an example, not a universal spec.

For the general GM picture and late-model Chevrolet bulletins, see our P0175 guide for Chevrolet.

Which Buicks Can Set P0175

We checked GM's documents engine by engine:

• 3.6L V6 (LY7, LLT, LFY, LGX) — GM's 2008 OBD documentation for the Enclave's LY7 lists P0174 and P0175 as separate bank tests. GM's PIP5549A names bank 2 lean codes on the 2012–2019 Enclave with the LLT and LFY, and GM engineering information names them on the 2017 LaCrosse with the LGX. These Buicks have two monitored banks.
• 4.6L Northstar V8 (Lucerne) — GM's 2008 OBD group covering the Lucerne's 4.6L lists P0174 and P0175.
• 3800 V6 (L26) — LaCrosse, Allure, Lucerne 3.8L: GM's 2008 OBD documentation for this engine lists P0171 and P0172 but no P0174 or P0175. On a 3800 Buick the rich code is P0172, covering the whole engine.
• Four-cylinder and three-cylinder Buicks — Encore, Encore GX, Envista, Verano, Regal and Envision four-cylinders, LaCrosse 2.4L: one bank only. They set P0172, never P0175.

If a scan tool shows P0175 on a four-cylinder Buick, check that the tool has the right vehicle selected before you diagnose anything.

Where Bank 2 Is

GM numbers the 3.6L V6 so that the bank with cylinder 1 is bank 1 — the right bank viewed from the flywheel end. Bank 2 holds 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 — and much easier to reach.
• 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.

P0175 Alone vs With P0172

Both banks breathe through the same MAF and share the same fuel supply and PCV system. A one-bank rich condition is hard to create with any of those, so P0175 by itself usually narrows the search to that bank's injectors.

What GM Has Documented

GM has published far fewer Buick-specific documents on P0175 than on its lean cousins. Here is what we found, and what we didn't.

2010 LaCrosse: high-pressure fuel pump

GM preliminary information PI-0145, indexed by NHTSA for the 2010 LaCrosse along with related Cadillac, Chevrolet and GMC models, describes a check engine light with P0172 and P0175 and an engine that runs rough, with the instruction to follow diagnosis and replace the high-pressure fuel pump. We have read only NHTSA's summary, not the document itself, so treat it as a pointer rather than a procedure. Note it lists both rich codes — a shared-cause pattern.

Fuel in the crankcase

On late-model GM V8 trucks GM has documented raw fuel in the oil as a cause of P0172 and P0175, and on the Buick Regal and Envision 2.0L turbo GM's bulletins 18-NA-246 and 22-NA-056 document the same mechanism for P0172. We found no GM document applying this to a Buick V6, but the physics is the same: if the oil is overfull and smells of gasoline, the PCV system is feeding fuel to both banks. Check the dipstick before buying parts.

The injector bulletin that doesn't apply

GM bulletin 20-NA-098 warns that installing the wrong flow-class injector skews fuel trims and lists P0175. It is widely quoted — but its brand list is Cadillac, Chevrolet and GMC, and its engine list is the 4.3L V6 and GM V8s such as the 5.3L and 6.2L — no Buick 3.6L. It does not name Buick. The lesson still holds for any direct-injected engine: if P0175 appeared after injector work on your 3.6L, have the parts checked against the GM catalog by VIN.

What GM's service information says about O2 sensors

GM's service information for its V6 fuel trim codes states that an oxygen sensor will not cause this code without also setting its own sensor codes, and tells technicians not to replace one to address it. If P0175 is the only code, the sensor is probably telling the truth.

Symptoms of P0175

• Check engine light on
• Fuel smell from the exhaust
• Oil above full and smelling of gasoline (shared PCV cause)
• Poorer fuel economy
• Rough idle or misfire codes on cylinders 2, 4 or 6 if the bank is very rich
• P0172 alongside when the cause is shared
• Later, P0430 if a rich bank 2 overheats its catalytic converter

Causes and How to Confirm Each

How Is P0175 Diagnosed?

1. Confirm the engine. A four-cylinder or 3800 V6 Buick should not set P0175.
2. Record all codes and freeze frame. Fix misfire, injector, MAF, MAP and EVAP codes first — they block the test.
3. Note whether P0172 is also stored. One bank or both is the main fork.
4. Check the oil for overfill and fuel smell.
5. Watch live trims for both banks hot at idle and at a steady cruise.
6. Command purge off and see whether the trims recover.
7. Check fuel pressure desired vs actual.
8. Run an injector balance test on bank 2, and verify any replaced injectors against the GM catalog by VIN.
9. Unplug the MAF and see whether both banks shift.
10. Clear codes and drive long enough in closed loop for the fuel trim monitor to complete.

Parts and Cost

GM Documents Relevant to P0175 on Buick Models

We found no current GM service bulletin that names P0175 specifically for a Buick and provides a repair procedure. These are the most relevant GM documents we read or found.

Have a dealer check your VIN against current bulletins rather than relying on any article, including this one. The check is free.

What Other P0175 Pages Get Wrong

• Listing P0175 for the 3800 V6. GM's documentation for the 3.8L lists only bank 1 fuel trim codes.
• Listing P0175 for four-cylinder Buicks. An Encore, Verano or four-cylinder Regal sets P0172.
• Putting bank 2 at the firewall on an Enclave. On the transverse 3.6L, bank 2 is the front bank.
• "P0175 means a bad O2 sensor." GM's service information says not to replace one for this code without sensor codes.
• Quoting 20-NA-098 for a Buick. Its brand list does not include Buick.
• Blaming the purge valve coverage. GM's Buick purge valve coverages list lean codes and EVAP codes, not P0175.

Frequently Asked Questions

Which side is bank 2 on a Buick Enclave?

The front bank, nearest the radiator. Bank 1, with cylinder 1, is the rear bank by the firewall.

Can a 3.8L Buick LaCrosse set P0175?

According to GM's 2008 OBD documentation for the 3800 V6, no — that engine has bank 1 fuel trim codes only. A rich 3800 sets P0172.

Is P0175 serious?

Not usually immediate, but a rich bank washes oil off cylinder walls, dilutes the oil and can overheat that bank's catalytic converter. Fix it before it becomes a P0430.

Can a bad O2 sensor cause P0175?

GM's service information says not without also setting oxygen sensor codes. If P0175 is the only code, look for a real rich condition.

What does P0172 plus P0175 mean on my Buick?

Both banks are rich, so look at what they share: fuel pressure, the high-pressure pump, fuel in the oil, purge flow, the MAF and the air intake.

Is there a Buick recall or special coverage for P0175?

We found none. A dealer can check your VIN for open campaigns and bulletins for free.