P0172 Code on a GMC: Fuel Trim System Rich, Bank 1 (GMC Guide)

P0172 on a GMC is "Fuel Trim System Rich, Bank 1." The engine computer has been pulling fuel out of bank 1 for so long that it has hit its limit, and the mixture is still rich. Most pages tell you to replace injectors or the oxygen sensor. GM's GMC documents say something else. On the 2018–2021 Terrain 2.0T, GM blames gasoline collecting in the engine oil from short trips and says a new high-pressure pump or injectors won't fix it. On the 2018–2022 Terrain 1.5T, the cause can be a charge air cooler tube that has popped off the throttle body. And on a 2.7L turbo Sierra or Canyon that has had engine work, GM has found the cam actuators fitted to the wrong camshafts.

What Does P0172 Mean on a GMC?

Your GMC's engine control module (ECM) trims fuel continuously from the upstream oxygen sensor. Short-term fuel trim is the instant correction; long-term fuel trim is the learned one. Negative numbers mean the ECM is taking fuel away because it sees rich exhaust. P0172 sets when bank 1's correction sits at its rich limit in closed loop and the mixture still reads rich.

Rich has fewer causes than lean, and they split into two groups: extra fuel the ECM didn't command (a leaking injector, a high-pressure pump pushing fuel into the oil, fuel vapor from the crankcase or the EVAP canister) and air the ECM thinks it has but doesn't (a MAF reading high, or boost air escaping after the MAF on a turbo engine). GM's GMC documents land in both groups.

For background across all GM brands, see our guide to MAF, MAP and O2 sensors. This page focuses on GMC.

Which GMCs Set P0172 — and Where Bank 1 Is

• V8 Sierra, Yukon, Yukon XL and Savana and the 4.3L V6: bank 1 is the driver's side. The bank 2 rich code is P0175.
• Acadia and Terrain 3.6L V6 (transverse): bank 1 is the rear bank, by the firewall.
• Four-, five- and six-cylinder inline engines — Terrain 1.5T, 2.0T and 2.4L, Acadia 2.5L, 2.0T and 2.5T, Canyon 2.5L and 2.7T, 2004–2012 Canyon, Envoy 4.2L and the 2.7L Sierra: bank 1 is the whole engine, and there is no P0175.
• 3.0L Duramax diesel (Sierra 1500, Yukon): GM has a bulletin that names P0172 on this diesel, covered below. Don't apply gas-engine advice to it.

Terrain: Fuel in the Oil and the Loose CAC Tube

2018–2021 Terrain 2.0T: short trips, not a bad part

GM bulletin 18-NA-246 covers the 2018–2019 Terrain with the 2.0L turbo (LTG), and 22-NA-056 covers the 2020–2021 Terrain 2.0T. The complaint is a check engine light with P0172, sometimes with P06DE and/or P0521. GM's cause: driving in short intervals lets excessive fuel collect in the crankcase. The crankcase vapors carry that fuel back into the intake, and the ECM sees rich exhaust it didn't create.

GM's wording is blunt: replacing the high-pressure fuel pump or injectors will not correct P0172 under these conditions unless those parts are verified as causing a rich condition. GM's confirmation in 22-NA-056:

• Long-term fuel trim should be a large negative number, −18% to −30%.
• If unplugging the MAF sensor does not bring long-term trim into the normal −10% to +10% range, check the crankcase for an overfilled oil level with a strong fuel smell.
• The repair is an oil and filter change, then clear the code and test drive. 18-NA-246 adds software and a revised PCV valve depending on model year; GM notes 2019 vehicles built after May 7, 2019 may already have the updated PCV (check the engine unit number).

GM also says owners who keep driving this way must change oil more often than the oil life monitor indicates.

2018–2022 Terrain 1.5T: the charge air cooler tube

On the 1.5L turbo (LYX), boost air goes from the turbo through the charge air cooler to the throttle body. If that tube comes off, the MAF has already counted air that never reaches the cylinders — so the ECM fuels for air that isn't there. GM's 22-NA-224 covers the 2018–2022 Terrain 1.5L with reduced engine power and any of P0101, P0172, P0299, P0506 or P1101, caused by the charge air cooler outlet tube separating at the throttle body. GM says to confirm the connection, inspect the tube, retainer clip and throttle body for damage, and replace the throttle body or MAF only if damaged or proven faulty. PIP5710 covers the same thing on the 2020 Terrain: push the tube down until the retainer snaps.

For 2019 Terrains still in dealer stock, GM issued service update N192266090 to fit a charge air cooler retainer kit, listing the same codes plus rough running and possible stalling at low speed or idle.

2010–2017 Terrain 2.4L: the high-pressure pump

GM's PIP6113 (May 2026) covers the 2010–2017 Terrain 2.4L (LAF, LEA) that stalls at a stop with P0191 and occasionally P0172. GM's cause is an aftermarket high-pressure fuel pump. A genuine pump carries a QR code and a GM part number; if yours doesn't, GM says to fit an original pump. Separately, GM emission recall 43180 replaced the high-pressure pump on certain 2010–2011 Terrain 2.4L models because a worn plunger seal could leak fuel into the crankcase — the recall doesn't name a DTC, but fuel in the oil is exactly what pushes trims rich. A dealer VIN check will show whether it was done.

Sierra, Yukon and Canyon

2014–2018 Sierra 1500 and 2015–2018 Yukon: casting flash at the MAF

PIP5446A covers the 4.3L LV3, 5.3L L83 and 6.2L L86 with harsh 1–2/2–3 shifts, a sputter at light throttle, rough idle and P0101, P0171, P0172, P0174 or P0175. Excess casting flash in the air filter housing near the MAF disturbs the reading. The fix is a new lid, checked for flash.

2014–2020 V6 and V8 trucks: the wrong injector

GM's 20-NA-098 applies to V6 and V8 gas engines including the 4.3L LV3, 5.3L L83/L84/L82, 6.2L L86/L87/L8B and 6.6L L8T. GM has seen the incorrect fuel injector installed during service, skewing fuel trims and setting codes including P0172 and P0175. If P0172 appeared right after an injector repair, check the part and flow class against the VIN before anything else.

2019–2026 Sierra 1500 and 2023–2026 Canyon 2.7T: actuators on the wrong cams

PIP6115 covers the 2.7L L3B in the 2019–2026 Sierra 1500 and 2023–2026 Canyon. After any repair that removed the camshaft actuators — a cam carrier reseal, for example — the truck may set P1101 and P0172, crank and not start, stall when taken off idle, refuse to go over 2,500 rpm, or have no power. GM's cause: the intake and exhaust actuators were installed on the wrong camshafts. Each is marked with a part number and an I or E on its front face.

2022–2025 Sierra 1500 and Yukon 3.0L Duramax

Bulletin 22-NA-128 covers the 3.0L diesel (LM2, LZ0) in the Sierra 1500 and Yukon with P0172, P026D, P2459 and/or P2A00, and gives a procedure to test the intake manifold for leaks. This is a diesel-specific fault — it doesn't apply to gas engines.

Older GMCs

NHTSA indexes several older GM documents naming P0172 on GMCs: P0172 on the 2003–2004 Envoy 4.2L LL8 (01181C), a 2004 document on a possible false P0172 on the I6 Envoy, P0133 with P0172 on the 2003–2004 Envoy, an engineering investigation (EI07239) on the 2007–2008 Sierra and Yukon 5.3L LMG/LC9 listing P0172 among injector-related codes, and PI-0145 for the 2010 Terrain (P0172 and P0175, rough running, high-pressure pump after diagnosis). We could read only NHTSA's summaries, so treat these as leads for a dealer to look up.

Symptoms of P0172

• Check engine light, sometimes with nothing else
• Fuel smell from the exhaust or the oil dipstick
• Oil level rising on the dipstick (fuel dilution on the Terrain 2.0T)
• Reduced engine power message (Terrain 1.5T CAC tube)
• Rough idle, stalling at a stop (Terrain 2.4L with an aftermarket pump)
• No start or no power above 2,500 rpm after engine work (2.7L L3B)
• Poor fuel economy

Causes and How to Confirm Each

How Is P0172 Diagnosed?

1. Record codes and freeze frame. Fix misfire, MAF, injector and boost codes first.
2. Check for P0175 on a V6 or V8 — both banks rich points at a shared cause like the MAF, oil dilution or purge.
3. Pull the dipstick. An overfull level that smells of fuel on a Terrain 2.0T points straight at GM's short-trip bulletins.
4. Look at the charge air cooler tube on a Terrain 1.5T before anything else.
5. Read live trims hot at idle and at 2,500 rpm, then do GM's MAF unplug test if fuel dilution is suspected.
6. Command purge off and watch whether trims recover.
7. Ask about recent work. New injectors (20-NA-098), cam actuator removal on a 2.7L (PIP6115) or a non-GM high-pressure pump (PIP6113) are documented causes.
8. Test fuel pressure and injectors only after the free checks.
9. Clear codes and drive long enough for the fuel trim monitor to run again.

Parts and Cost

GM Documents That Name P0172 on GMC Models

Have a dealer check your VIN for current bulletins, recalls and special coverages rather than relying on any article, including this one.

What Other P0172 Pages Get Wrong

• "Replace the injectors." On the Terrain 2.0T, GM says new injectors or a pump won't fix fuel-diluted oil.
• "Replace the O2 sensor." None of the GMC documents above fixes P0172 with an oxygen sensor.
• Treating it as a fuel problem on a turbo. On the Terrain 1.5T, the cause can be a boost tube off the throttle body.
• Forgetting recent repairs. GM documents wrong injectors after service and swapped cam actuators on the 2.7L.
• Assuming two banks. On a Terrain, Canyon four-cylinder, Envoy I6 or 2.7L Sierra, there is only bank 1.
• Not checking the dipstick. Fuel in the oil is free to spot and GM's top cause on the 2.0T.

Frequently Asked Questions

Is P0172 serious on a GMC?

It can be. A rich engine wastes fuel and can overheat the converter, and fuel-diluted oil protects the engine less well. Diagnose it promptly.

Why does my Terrain 2.0T keep setting P0172 in winter?

Short, cold trips are when fuel collects in the oil. GM's 18-NA-246 and 22-NA-056 describe exactly this; the repair is an oil change, and GM says owners who keep driving that way need more frequent oil changes.

My Terrain 1.5T lost power and set P0172. What should I check?

The charge air cooler tube at the throttle body. GM's 22-NA-224 and PIP5710 show it can separate; it should snap back on with the retainer engaged.

Can a bad MAF sensor cause P0172 on my Sierra?

Yes, if it over-reports airflow. On 2014–2018 Sierra 1500s GM's PIP5446A found casting flash in the air box disturbing the MAF — check the lid before replacing the sensor.

P0172 appeared after my 2.7L Sierra had engine work. Coincidence?

Possibly not. GM's PIP6115 says swapped intake and exhaust cam actuators can set P1101 and P0172 or cause a no-start.

Will GM pay for a P0172 repair?

Only if your vehicle is under warranty or a recall or coverage applies. A dealer VIN check is free; we can't promise coverage.