P0275 on 2017-2018 GMC Sierra 3500: Cylinder 5 Balance Fault Causes and Fixes

What's Unique About the 2017-2018 Gmc SIERRA 3500

The 2017-2018 Sierra 3500 uses the L5P Duramax engine, which features a high-pressure common-rail fuel system with Denso solenoid-style injectors. While generally reliable, these injectors are sensitive to fuel quality and can fail internally or become clogged. A more frequent issue is the injector's electrical connector pigtail developing high resistance or a poor connection, which is a known failure point on L5P engines. Additionally, GM has issued Technical Service Bulletin #17-NA-171, which notes that P0275 can be set due to a software anomaly in the ECM, requiring a reflash to correct various drivability issues. [Bulletin #17-NA-171]

Diagnostic Flowchart

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

Symptoms You May Notice

• Rough or vibrating idle
• Reduced engine power and slower acceleration
• Excessive white or black smoke from the exhaust
• Noticeable smell of raw diesel fuel
• Decreased fuel economy
• Check Engine Light (MIL) is on
• Hesitation or stumble during light acceleration

Most Likely Causes

1. Failed Fuel Injector 🔴 High Probability The high-pressure injectors on the L5P can fail internally due to wear, contamination from poor fuel quality, or simply high mileage (often noted between 50,000-70,000 miles).
   How to confirm: Use a capable scan tool to monitor injector balance rates at idle and operating temperature. Per GM, a value greater than +/- 4.0 mm³ in park indicates a problem. A high positive number for cylinder #5 means the ECM is adding fuel to compensate for a weak contribution. A cylinder cutout test should also show little to no change in engine RPM when cylinder #5 is deactivated.
   Typical fix: Replace the cylinder #5 fuel injector and its associated seals and high-pressure line. The new injector's flow rate code (found on the injector body) must be programmed into the ECM.
   Est. part cost: $280-$400 for an OEM Denso injector.
2. Faulty Injector Wiring or Connector 🟡 Medium Probability The injector connector pigtail is a very common failure point on the L5P Duramax. The connector can develop high resistance from vibration and fretting corrosion over time, especially when exposed to moisture, leading to intermittent signals and codes like P0275 or P0205.
   How to confirm: Visually inspect the wiring harness and connector for cylinder #5 for any signs of damage, corrosion, or loose pins. Wiggle the connector with the engine running to see if it affects the idle. Use a multimeter to check for proper voltage and ground at the connector. Often, the issue is internal to the connector and not visually apparent; look for fine black powder, a sign of fretting. 🎬 Watch: How to ice pick a connector for a better connection.
   Typical fix: Replace the injector connector pigtail. It is highly recommended to use an OEM pigtail (GM Part #19368140) and solder the connections with heat-shrink tubing for a durable, weather-resistant repair.
   Est. part cost: $25-$60 for an OEM pigtail.
3. Clogged or Dirty Fuel Injector 🟡 Medium Probability Poor quality diesel fuel or contaminants can lead to carbon and other deposits forming inside the injector, restricting fuel flow and disrupting the spray pattern.
   How to confirm: This is difficult to confirm without first ruling out electrical and mechanical failure. If balance rates are high but the injector's electrical circuit is good, a clog is likely. This is a diagnosis of exclusion before replacing the injector.
   Typical fix: A professional-grade direct fuel injector cleaning service may restore function. However, for severe clogs, replacement is the only reliable solution. Using a quality diesel fuel additive regularly can help prevent this issue.
   Est. part cost: $100-$200 for cleaning service, or the cost of a new injector if unsuccessful.
4. Engine Control Module (ECM) Anomaly ⚪ Low Probability As noted in TSB #17-NA-171, an anomaly within the ECM software can cause P0275 and a host of other codes to set without a true mechanical fault, often accompanied by various drivability complaints. [Bulletin #17-NA-171]
   How to confirm: This is a diagnosis of exclusion. If the injector, wiring, and fuel system are all confirmed to be good, the ECM becomes the primary suspect. A GM dealer or qualified shop must check for available software updates for both the ECM and TCM.
   Typical fix: Reprogram the ECM and TCM with the latest software calibration from GM. The TSB specifies that both modules must be updated together. [Bulletin #17-NA-171]
   Est. part cost: $100-$250 for dealer reprogramming if not covered by warranty.

Rare But Worth Checking

• Internal Engine Mechanical Failure: While rare, a loss of compression in cylinder #5 due to a piston, ring, or valve train issue (like a broken pushrod as mentioned in bulletin PIP5537) could also cause a contribution fault. This would typically be accompanied by other severe symptoms like a rhythmic ticking noise and is a worst-case scenario requiring a compression test to confirm.

Diagnosis Steps

1. Check for other DTCs to see if P0275 is part of a larger pattern, such as other injector codes or the codes listed in TSB 17-NA-171. [Bulletin #17-NA-171]
2. Connect a professional scan tool and view live data for injector balance rates. With the engine at full operating temperature and in Park or Neutral, check the values. Look for cylinder #5 to be significantly different from the others, ideally outside the +/- 4.0 mm³ range. Some sources suggest a wider tolerance of +/- 6.0 mm³ when in Drive with the service brake applied.
3. Perform a cylinder cutout test (if available on the scan tool). Deactivating cylinder #5 should result in minimal change to the engine's idle if it's already not contributing.
4. Thoroughly inspect the wiring harness and electrical connector for cylinder #5. The cylinder numbering on the L5P is 1, 3, 5, 7 on the passenger side (right bank) and 2, 4, 6, 8 on the driver's side (left bank). Cylinder 5 is the third one back on the passenger side. Check for chafing, breaks, or corrosion. Given the high failure rate, consider replacing the pigtail even if it looks okay.
5. If the wiring is confirmed good, swap the #5 injector with another cylinder on the same bank (e.g., #3 or #7). Clear the codes and run the engine. If the code changes to P0273 (Cylinder 3) or P0277 (Cylinder 7), the injector is faulty.
6. If the code remains P0275 after the swap, the issue is with the wiring to that cylinder or the driver circuit in the ECM.
7. If all else fails and no mechanical or electrical fault is found, consult a GM dealership to check for and apply ECM/TCM software updates as per TSB #17-NA-171. [Bulletin #17-NA-171]

Parts You'll Likely Need

• Fuel Injector (OEM #12698552) — This is the most common cause of a cylinder-specific contribution fault on the L5P Duramax when the connector is not the issue. This part number supersedes 12674615, 12678992, 12686812, and 12696966.
  Trusted brands: Denso (OEM), ACDelco
  OEM price range: $280-$400
  Aftermarket price range: $200-$300 (Remanufactured)
• Fuel Injector Connector Pigtail (OEM #19368140) — The electrical connector is a known weak point and a very common failure, causing an intermittent injector circuit fault that sets contribution codes.
  Trusted brands: ACDelco (OEM), Fleece Performance, Dorman
  OEM price range: $30-$50
  Aftermarket price range: $15-$30
• High-Pressure Fuel Line (Cylinder 5) (OEM #12685923) — GM service procedure mandates replacing the small high-pressure fuel line that connects the fuel rail to the injector any time it is removed to ensure a perfect, leak-free seal under extreme pressure. This line fits cylinders 2, 4, 5, and 7.
  Trusted brands: ACDelco (OEM)
  OEM price range: $40-$60
  Aftermarket price range: $30-$50

Related Codes That Often Appear With This One

• P0305 — If the contribution issue is severe enough, the ECM will also register it as a definitive misfire on cylinder 5.
• P0205 — This code indicates a malfunction in the injector circuit for cylinder 5, pointing more specifically to an electrical problem like a bad connector, wiring, or a failed injector solenoid.

Technical Service Bulletins (TSBs) & Recalls

• 17-NA-171: Mentions P0275 as potentially being caused by an ECM/TCM software anomaly requiring an update.
• PIP5468F: Lists P0275 in a large group of codes related to engine performance issues, directing technicians to follow standard diagnostic procedures.
• PIP5537: Details engine misfire diagnosis related to potential valvetrain issues (like broken pushrods) that could also manifest as a contribution code like P0275.

Platform-Specific Known Issues

• TSB #17-NA-171: Explicitly lists P0275 among a long list of DTCs that can be caused by an ECM software anomaly, requiring reprogramming of both the ECM and TCM. [Bulletin #17-NA-171]
• TSB #23-NA-027: Provides a detailed procedure for diagnosing injector connector fretting corrosion ('black powder') and gives specific labor time allowances for replacing the pigtail for cylinders #1, 5, or 7.
• Injector Connector Fretting: The electrical connector pins for the injectors are prone to fretting corrosion due to engine vibration, leading to high resistance and intermittent open circuits. This is a more common failure point than the injector itself.

Mechanic-Grade Diagnostic Values

• Injector Balance Rate (Hot Idle) — expected: +/- 4.0 mm³ in Park/Neutral. Some technicians use a limit of +/- 6.0 mm³ in Drive with the brake applied.. Failure: A value consistently outside the expected range. High positive values mean the ECM is adding fuel to compensate for a weak cylinder.
• Injector Connector Resistance — expected: A healthy connection should have very low resistance, near 0.8 ohms.. Failure: Resistance climbing to 3.8 ohms or higher indicates a poor connection, often due to fretting corrosion.
• Injector Solenoid Resistance — expected: Generally between 10-18 ohms, but no specific OEM value for the L5P is published. The key is that all injectors should have nearly identical resistance.. Failure: An injector with a resistance value that is significantly different (e.g., more than 1 ohm) from the others, or is open/shorted.
• Injector Connector Voltage (Key On, Engine Off) — expected: One pin should show battery voltage (~12V).. Failure: No voltage or significantly low voltage points to a wiring issue upstream of the connector.
• Injector Voltage Waveform (Engine Running) — expected: Using an oscilloscope, expect to see a square wave pattern showing battery voltage, dropping to near zero when the ECM commands the injector on, followed by a large inductive voltage spike (e.g., 50V+) when the circuit opens.. Failure: A missing or distorted pattern indicates a problem with the ECM driver or wiring. Comparing the waveform from cylinder 5 to a known-good cylinder is the best diagnostic method.

Scan Tool Commands That Help

• GM GDS2: Injector Flow Rate Programming — This is a mandatory step after replacing a fuel injector. The unique Injector Quantity Adjustment (IQA) code from the new injector must be programmed into the ECM. The path is: ECM > Module Diagnostics > Engine Control Module > Control Functions > Configuration Reset > Injector Flow Rate Programming.
• Aftermarket (Snap-on, Autel, etc.): Injector Rate Programming / Injector Quantity Adjustment (IQA) — Used after replacing an injector to program the new IQA code. The menu path is typically under Engine > Functional Tests or Special Functions. Note: Some L5P IQA codes begin with 'F7'; if the scan tool has a separate field for this, do not enter it with the main code.
• GM GDS2 / Professional Scan Tool: Cylinder Power Balance / Cylinder Cutout Test — Used to confirm which cylinder is underperforming. The tool deactivates one injector at a time. If deactivating cylinder 5 causes little or no change in engine RPM, it confirms it was not contributing properly.

Wiring & Ground Locations

• Injector Harness Chafe Point 1 — Where the main engine wiring harness passes the steering shaft.. Constant movement from steering can cause the harness to rub against the shaft, eventually wearing through the insulation and causing a short or open circuit for one of the injector wires.
• Injector Harness Chafe Point 2 — Along the edges of the valve covers, especially where the harness is secured by clips.. Engine vibration can cause the harness to rub against the sharp metal edge of the valve cover, leading to wire damage.
• Cylinder 5 Injector Connector (X135) — Third connector back from the front on the passenger side (right bank) valve cover.. This specific connector is the interface to the injector. It is highly prone to fretting corrosion, which appears as a fine black powder and causes high resistance, triggering P0275 and related circuit codes like P0205.

Real Owner Repair Stories

• YouTube user 'c farmer' (2018 L5P Duramax with over 500,000 miles on the original engine.) — Dead miss, reduced engine power message, service emissions system message, and codes P0205/P0305.
  ❌ Tried (didn't work) The owner did not report trying other fixes first, as he was experienced with the issue.
  ✅ What actually fixed it Replacing the fuel injector connector pigtail for the affected cylinder. The owner states that in over half a million miles of driving, every time he had a misfire code, the cause was a failed pigtail, never the injector itself.

"I Checked Everything" — The Actual Cause

• A common misdiagnosis pattern for P0275 involves assuming a fuel delivery problem that can be found with a pressure test or smoke test. However, the root cause is often electrical fretting inside the injector connector. All fuel pressure tests will pass, and a smoke test will show no leaks, but the high resistance in the connector intermittently prevents the injector from firing correctly. The fix is not fuel-system related, but rather replacing the electrical pigtail.

OEM Part Supersession History

• 12674615, 12678992, 12686812, 12696966 → 12698552 — Standard part evolution for reliability and manufacturing improvements.
  Heads up: The newest part number (12698552) is the correct service replacement for all previous versions on the 2017-2018 L5P engine.

Model Year Variations Within This Range

• 2017-2019: These models were equipped with the Allison 1000 6-speed automatic transmission. While reliable, its behavior and diagnostics differ from the 10-speed Allison introduced in 2020.
• 2017+: The Engine Control Module (ECM) on all L5P engines is encrypted, which initially made aftermarket tuning complex, requiring an ECM swap or a specialized unlock service. This is relevant if considering tuning as part of a repair or upgrade.