P0175 on 2014-2018 GMC Yukon Denali: System Too Rich Bank 2 Causes and Fixes

What's Unique About the 2014-2018 Gmc YUKON DENALI

On these specific GM trucks with the 6.2L L86 direct-injection engine, a rich condition (P0175 and often P0172) is frequently caused by issues beyond typical fuel system faults. A primary, well-documented problem is the internal failure of the camshaft-driven high-pressure fuel pump (HPFP). When it fails, it leaks raw fuel directly into the crankcase, which then gets pulled into the intake via the PCV system, creating a rich condition that the PCM cannot correct. Another documented issue is an incorrect fuel alcohol percentage reading from the flex-fuel sensor, causing the PCM to inject too much fuel (Bulletin #PIP4792D). Finally, manufacturing defects like casting flash near the MAF sensor have also been identified by GM as a cause of turbulent airflow and rich codes (Bulletin #PIP5446A).

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: The 2014-2018 range covers two generations: the end of the 3rd gen (GMT900, 2014 model year) and the start of the 4th gen (K2XX, 2015-2018 model years). Both primarily use a 6.2L V8, but the K2XX platform introduced the L86 EcoTec3 engine with direct injection. Issues like the high-pressure fuel pump failure are specific to the 2015-2018 models with direct injection. The MAF casting flash issue (TSB PIP5446A) applies to 2014-2017 models.

Symptoms You May Notice

• Check Engine Light is on
• Rough idle, especially after sitting for a while
• Strong smell of gasoline or rich exhaust fumes
• Black smoke from the exhaust pipe
• Decreased fuel economy
• Hesitation or lack of power during acceleration
• Hard shifting or surging transmission feel
• Engine continues to run for a few seconds after shutoff (dieseling)
• Strong smell of gasoline from the engine oil dipstick
• Rising oil level on the dipstick

Most Likely Causes

1. Leaking or Faulty High-Pressure Fuel Pump (HPFP) 🔴 High Probability The direct-injection 6.2L L86 engine (2015-2018) has a high-pressure fuel pump that is a well-documented, common failure point. The internal seals fail, allowing fuel to leak directly into the crankcase. This is a known issue on this platform, often triggering P0172 and P0175 codes, especially after extended idling.
   How to confirm: This is the most definitive cause if you find fuel in the engine oil. Check the dipstick for a rising oil level and a strong gasoline smell. A technician can also isolate the PCV system; if fuel trims return to normal after disconnecting the dirty air side of the PCV and plugging the vacuum source, it's a strong indicator the HPFP is leaking fuel vapor into the intake.
   Typical fix: Replacement of the high-pressure fuel pump, the fuel feed line, and intake manifold gaskets. An oil change is mandatory to remove contaminated oil.
   Est. part cost: $300-$600 for the pump, plus gaskets and fuel line.
2. Dirty or Faulty Mass Airflow (MAF) Sensor 🟡 Medium Probability The MAF sensor can become contaminated with dirt and oil, causing it to send inaccurate (high) airflow readings to the computer. GM also issued a TSB (#PIP5446A) regarding casting flash (excess plastic) in the air filter housing near the sensor that can disrupt airflow and trigger this code.
   How to confirm: Inspect the MAF sensor wires for contamination. With a scan tool, monitor MAF readings. At idle, the g/s reading should be close to the engine's displacement in liters (e.g., ~6.2 g/s). Also, inspect the inside of the air filter housing for plastic flashing near the MAF sensor mounting point.
   Typical fix: Clean the sensor with a dedicated MAF sensor cleaner spray. If cleaning doesn't resolve the issue, or if casting flash is found, the sensor or air filter housing lid may need to be replaced.
   Est. part cost: $10-$20 for cleaner, $80-$150 for a new sensor.
3. Incorrect Fuel Alcohol Content Reading 🟡 Medium Probability For flex-fuel enabled Yukons, the PCM learns the fuel's ethanol content without a dedicated sensor. Short trips or refueling with small amounts can corrupt this learned value. If the PCM thinks the tank has E85 but it's filled with regular gasoline, it will command a much richer mixture, causing P0175. TSB #PIP4792D specifically addresses this.
   How to confirm: Use a scan tool to view the "Fuel Alcohol Content" parameter. If the reading is high (e.g., over 15-20%) but the tank is filled with regular gasoline, the reading is skewed.
   Typical fix: Resetting the fuel alcohol content value using a capable scan tool. After the reset, the fuel trims should also be reset.
   Est. part cost: $0 for a reset if you have the tool, or a shop diagnostic fee.
4. Leaking Fuel Injector(s) ⚪ Low Probability
   How to confirm: Perform a fuel pressure leak-down test. After shutting the engine off, the fuel rail pressure should hold steady. If it drops quickly, it may indicate a leaking injector. You can also pull the spark plugs on Bank 2 and check for one that is black, sooty, and wet with fuel.
   Typical fix: Replace the faulty fuel injector(s) on Bank 2.
   Est. part cost: $50-$150 per injector.
5. Faulty Upstream Oxygen (O2) Sensor ⚪ Low Probability
   How to confirm: While an O2 sensor can fail, it's more often correctly reporting a problem caused by something else. A scan tool can be used to graph the O2 sensor voltage. A sensor that is stuck reading high (e.g., >0.8V) and is not responsive could be faulty, but this should only be considered after ruling out all other causes of a true rich condition.
   Typical fix: Replace the Bank 2, Sensor 1 (upstream) oxygen sensor.
   Est. part cost: $50-$120

Rare But Worth Checking

• EVAP Purge Valve Stuck Open: If the EVAP purge valve sticks open, it can allow un-commanded fuel vapors from the gas tank to enter the intake manifold, creating a rich condition. This can be diagnosed by commanding the valve closed with a scan tool and checking if fuel trims normalize, or by using a smoke machine.
• High Fuel Pressure (Non-HPFP): A failing fuel pressure regulator or a restriction in the fuel return line (on non-DI models) can cause system-wide high fuel pressure, leading to rich codes on both banks (P0172 and P0175).

Diagnosis Steps

1. Use an OBD-II scanner to confirm P0175 and check for any other codes, like P0172 or P0101. Note the long-term fuel trim values for both banks.
2. Perform a sensory check. Smell the engine oil on the dipstick for a strong gasoline odor. A rising oil level is a definitive sign of HPFP failure.
3. If no fuel is in the oil, check the 'Fuel Alcohol Content' percentage with a scan tool (if flex-fuel capable). If it's incorrectly high (e.g., >20% with pump gas), perform a fuel composition reset.
4. Inspect the air intake system. Check for a dirty air filter. Locate and inspect the Mass Airflow (MAF) sensor for contamination. Also inspect the air filter housing for plastic 'casting flash' per TSB #PIP5446A.
5. Clean the MAF sensor using a dedicated MAF sensor cleaner. Allow it to dry completely, reinstall, clear codes, and test drive.
6. If codes return, perform a diagnostic test for the HPFP. Disconnect the 'dirty side' PCV hose from the intake and plug the intake port. Start the engine and monitor fuel trims. If they quickly return to normal (near 0%), the HPFP is leaking fuel into the crankcase.
7. If the HPFP test is negative, investigate other causes like a stuck-open EVAP purge valve or leaking fuel injectors via a fuel pressure leak-down test.
8. As a last resort, consider a faulty Bank 2 upstream O2 sensor, but only after all other fuel and air metering causes have been exhaustively ruled out.

Parts You'll Likely Need

• High-Pressure Fuel Pump (OEM #12641847)

Related Codes That Often Appear With This One

• P0172 — This is the identical 'System Too Rich' code but for Bank 1. When both appear together, it points to a problem affecting the entire engine, such as the MAF sensor, fuel pressure, EVAP system, or most commonly on this platform, a failing high-pressure fuel pump.
• P0101 — This code relates to a MAF sensor performance issue. Its presence alongside P0175 strongly suggests the MAF sensor is the root cause, as mentioned in TSB #PIP5446A.

Technical Service Bulletins (TSBs) & Recalls

• PIP5446A: Addresses rough idle and rich/lean codes (P0171/P0172/P0174/P0175) caused by excessive casting flash in the air filter housing near the MAF sensor.
• PIP4792D: Addresses rich codes (P0172/P0175) and rough running due to the ECM incorrectly learning a high fuel alcohol content.
• 20-NA-200: Provides diagnostic tips for P0172/P0175 when SI does not isolate the cause, pointing towards a leaking high-pressure fuel pump as the likely culprit.

Platform-Specific Known Issues

• TSB #PIP5446A: Notes that casting flash (excess material from manufacturing) near the MAF sensor can disrupt airflow, causing codes P0172 and P0175. The fix is to inspect and remove the flashing.
• TSB #PIP4792D: Points to incorrect fuel alcohol content readings causing rich conditions. This requires checking the parameter with a scan tool and potentially performing a reset.
• High-Pressure Fuel Pump Failure: On 2015+ models with direct injection, the high-pressure fuel pump is a known failure point that can cause rich codes, often triggered by extended idling.

Mechanic-Grade Diagnostic Values

• Long-Term Fuel Trim (LTFT) — expected: Within +/- 10% at idle.. Failure: Consistently negative values, often -20% to -35%, show the ECM is compensating for a severe rich condition.
• High-Pressure Fuel System (HPFP) Pressure — expected: ~300-500 PSI at idle, rising to over 2,000 PSI under load.. Failure: While low pressure indicates a weak pump, for a rich code the pressure may be normal while the pump leaks internally into the crankcase.
• Low-Pressure Fuel System Pressure — expected: 50-60 PSI at idle on 2015+ L86 models.. Failure: Pressure below this range indicates a problem with the in-tank pump, not the HPFP.
• Mass Air Flow (MAF) Sensor Reading (Warm Idle) — expected: Approximately equal to the engine displacement in liters, so ~6.2 grams/second (g/s) for the 6.2L engine.. Failure: A reading significantly higher than expected can cause a rich condition. A reading significantly lower suggests an unmetered air leak.
• Upstream Oxygen Sensor (Bank 2, Sensor 1) Voltage — expected: Rapidly fluctuating between ~0.1V and 0.9V in closed loop.. Failure: Voltage is stuck high (e.g., >0.8V), indicating the sensor is correctly seeing a persistent rich mixture or the sensor itself has failed.

Scan Tool Commands That Help

• GDS2 or capable aftermarket scanner: Fuel Composition Reset — This is a critical first step for Flex Fuel vehicles when P0172/P0175 are present. If the learned alcohol content is incorrectly high, the ECM will command too much fuel. A reset forces the system to relearn the actual content from the fuel in the tank.
• GDS2 or capable aftermarket scanner: Fuel Trim Reset — After performing any repair for a fuel system code (like replacing a pump or sensor, or performing a fuel composition reset), the long-term fuel trim values should be reset. This clears the old learned adjustments and allows the ECM to build a new fuel map based on the fix immediately.

Wiring & Ground Locations

• G103 / G108 — Located on the back side of the cylinder heads.. These are major engine grounds. While not directly tied to P0175 in documentation, a poor ground connection here can cause erratic behavior from various engine sensors, leading to incorrect fuel calculations. Cleaning these grounds is a good practice when diagnosing elusive electronic issues.
• G102 — On the left side of the engine block, near the #3 cylinder, below the exhaust manifold.. This ground is for the ignition coils. While less likely to cause a rich code, a poor ground could theoretically affect spark quality and combustion efficiency, which is monitored by the O2 sensors.

Real Owner Repair Stories

• YouTube video by 'Pro Auto Diagnostics & Repair' (2014 Chevrolet Silverado 5.3L (similar DI system)) — Check Engine Light with codes P0172 and P0175 (rich on both banks).
  ❌ Tried (didn't work) Initial diagnosis pointed towards common issues.
  ✅ What actually fixed it The high-pressure fuel pump was leaking internally into the crankcase. The diagnostic involved disconnecting the PCV hose from the intake, plugging the intake port, and observing the fuel trims return to normal on the scan tool. The final repair was replacing the HPFP.
• Reddit user cited in Go-Parts.com article (2018 GMC Sierra 1500 5.3L V8 (similar DI system)) — Rough idle, weak acceleration, poor fuel mileage, codes P0172 & P0175.
  ❌ Tried (didn't work) Replaced MAF sensor, Replaced PCV valve, Replaced spark plugs, Replaced high-pressure fuel pump, Cleaned throttle body
  ✅ What actually fixed it After replacing numerous expensive parts with no success, the actual fix was a 'Fuel Alcohol Content Reset' performed with a scan tool. The vehicle's virtual sensor had incorrectly learned a high ethanol percentage, causing the computer to command a rich mixture.
• Chevrolet Forum user (2015 Silverado 72k miles) — P0172 and P0175 codes, especially after extended idling. Hard shifting and engine 'dieseling' (running on for a few seconds after shutoff).
  ❌ Tried (didn't work) The user was in the diagnostic phase.
  ✅ What actually fixed it The thread resolution pointed to checking the fuel alcohol content reading via a scan tool. A moderator noted that if the reading is skewed high (e.g., over 10% on regular gas), it will cause a rich condition and must be reset.

"I Checked Everything" — The Actual Cause

• In many cases on this platform, a smoke test for vacuum leaks will come back negative. The root cause is often not unmetered air (a vacuum leak) but rather unmetered fuel being introduced into the system. This typically happens via two main pathways: 1) The high-pressure fuel pump (HPFP) leaks fuel into the crankcase, which is then drawn into the intake manifold by the PCV system. 2) The Engine Control Module (ECM) incorrectly commands an overly rich mixture because its 'virtual' fuel alcohol sensor has learned an erroneously high ethanol content value.

When the Usual Fixes Don't Work

• A significant piece of counter-evidence to immediately suspecting and replacing the high-pressure fuel pump (HPFP) comes from a documented case where an owner replaced the HPFP, MAF sensor, PCV valve, and spark plugs without resolving the P0172/P0175 codes. The actual solution was a no-cost 'Fuel Alcohol Content Reset' performed with a scan tool. This proves that even with classic symptoms of HPFP failure (rich codes on both banks), the root cause can be a simple software/sensor calibration issue. This strongly suggests that performing the Fuel Composition Reset should be a mandatory diagnostic step before undertaking the expensive and labor-intensive HPFP replacement.

OEM Part Supersession History

• 12679090 → 12711668 — Part has been updated by GM, likely for improved reliability and to address the internal leaking issue.
  Heads up: This part number is for the 6.2L L86 V8. The part number 12641847, sometimes associated with rich codes, is for smaller 2.4L DI engines and is not compatible.
• 12625817 → Unknown — This is another widely cited OEM part number for the L83/L86 high-pressure fuel pump.
  Heads up: Ensure the part number matches the specific engine (L86 6.2L), as pumps for other GM DI engines (V6, 4-cyl) are physically different.

Model Year Variations Within This Range

• 2014 only: The 2014 model year is the last of the GMT900 generation and typically used the 6.2L L94 V8 with port fuel injection. It does not have the direct-injection system or the high-pressure fuel pump (HPFP) that is a primary cause of P0175 on later models. Causes on a 2014 are more likely related to traditional issues like leaking port injectors, a faulty fuel pressure regulator, or a bad MAF sensor.
• 2015-2018: These K2XX generation models use the 6.2L L86 V8 with direct injection. This introduces the high-pressure fuel pump (HPFP) as a very common failure point leading to P0175. They also use a 'virtual' flex-fuel sensor that can drift and require a scan tool reset, a cause not present on the older system.