P0274 on 2009-2014 Buick Enclave: Cylinder 5 Injector Circuit High Causes & Fixes

What's Unique About the 2009-2014 Buick ENCLAVE

On the Buick Enclave's 3.6L V6 engine (part of the GM Lambda platform), the fuel injector wiring harness is known to be susceptible to damage. A General Motors Technical Service Bulletin (TSB #PIP4924D) specifically advises technicians to inspect the harness for rubbing or chafing against the intake plenum, valve cover bolts, fuel lines, and the side of the cylinder head when encountering this and other related injector codes. Furthermore, cylinder 5 is located on the rear bank of the engine against the firewall, making access for diagnosis and repair significantly more difficult and labor-intensive than for the front cylinders.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light is on
• Rough or shaking idle
• Engine stumbling or hesitation during acceleration
• Noticeable loss of power
• Reduced fuel economy
• Engine vibration
• Strong fuel smell from the exhaust
• Black smoke from the exhaust

Most Likely Causes

1. Damaged Fuel Injector Wiring Harness 🔴 High Probability → Shop Engine Wiring Harness As documented in GM TSB #PIP4924D, the injector wiring harness on this platform can rub through its insulation. Specific chafe points include contact with the intake plenum, valve cover bolts, fuel lines, and the side of the cylinder head under the plenum.
   How to confirm: Visually inspect the entire length of the wiring harness leading to the cylinder 5 fuel injector. Pay close attention to the common chafe points mentioned in the TSB. Wiggle the harness with the engine running to see if it induces a change in idle quality.
   Typical fix: Repair the damaged section of the wire using solder and heat-shrink tubing. Protect the harness from future chafing using a protective wire loom, anti-abrasion tape, or by re-routing it away from sharp edges. If the connector is damaged, replace the pigtail.
   Est. part cost: $10-$30
2. Failed Cylinder 5 Fuel Injector 🟡 Medium Probability → Shop Fuel Injector The 3.6L V6 uses direct injection (GDI), and these injectors operate under high pressure and can fail electrically. Internal coil windings can short or open, leading to a circuit fault. Use of fuel with high ethanol content (like E10) can also contribute to premature wear by attracting moisture.
   How to confirm: With the engine off, disconnect the injector and measure its resistance with a multimeter. A healthy GM 3.6L direct injector should read between 1.2 and 1.8 ohms. A reading outside this range, or an infinite (OL) reading, indicates failure. You can also swap the injector with one from another cylinder (e.g., cylinder 3) and see if the trouble code follows to the new cylinder (P0268).
   Typical fix: Replace the faulty fuel injector. Since accessing the rear bank requires removing the intake manifold, it is highly recommended to replace all three rear injectors (1, 3, 5), their Teflon seals, and the intake gaskets at the same time.
   Est. part cost: $40-$150 per injector
3. Poor Connection at Injector or PCM ⚪ Low Probability
   How to confirm: Inspect the electrical connector at the fuel injector and the PCM for corrosion, bent/broken pins, or loose connections. Ensure the connector is fully seated and the locking tab is secure. Apply dielectric grease to the connection to prevent future moisture intrusion.
   Typical fix: Clean the connector terminals with electrical contact cleaner or repair the bent pins. Replace the connector pigtail if it is damaged.
   Est. part cost: $10-$30

Rare But Worth Checking

• Failed Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is the least likely cause. The internal driver circuit for the cylinder 5 injector can fail, but all other possibilities, especially wiring and the injector itself, must be exhaustively ruled out before condemning the PCM.

Diagnosis Steps

1. Scan the PCM for any other stored trouble codes to get a full picture of the issue.
2. Identify cylinder 5. On the 3.6L V6, it is on the rear bank (closest to the firewall), the rightmost cylinder when viewed from the front of the vehicle.
3. Detailed Wiring Inspection: Carefully inspect the fuel injector wiring harness, focusing on the specific chafe points identified in TSB #PIP4924D: against the intake plenum, at valve cover bolts, against fuel lines, and on the side of the head under the plenum.
4. Check for Signal: Disconnect the injector and use a 'noid light' to verify that the PCM is sending a pulse signal to the connector. No pulse points to a wiring or PCM issue.
5. Measure Injector Resistance: Use a multimeter set to Ohms to check the resistance of the fuel injector itself. A good injector for this engine should measure between 1.2 and 1.8 ohms. A reading of infinite ohms (OL) means the injector's internal coil is open, while a reading near zero means it is shorted.
6. Swap Injectors (Confirmation): If the wiring and signal are good, but the injector resistance is suspect, swap the cylinder 5 injector with another cylinder on the same bank (e.g., cylinder 3). Clear the codes and run the engine. If the code changes to P0268 (Cylinder 3 Injector Circuit High), the injector is confirmed to be faulty.
7. Check for Shorts to Voltage: If the code P0274 returns after the swap, the problem lies in the wiring or the PCM. Use a multimeter to check the signal wire at the injector connector for voltage with the key on; there should not be constant voltage present.
8. Final Check: If all wiring and the injector prove to be good, the final step is to suspect a faulty injector driver in the PCM.

Parts You'll Likely Need

• Fuel Injector (OEM #12638530 (superseded by 12669384)) — This is the most commonly replaced component to fix a P0274 code when wiring is not the issue. The original part number 12638530 is often superseded.
  Trusted brands: ACDelco (GM Genuine), Delphi, Bosch
  OEM price range: $80-$150
  Aftermarket price range: $40-$90
• Upper Intake Manifold Gasket Set (OEM #12673300 (ACDelco MS96994)) — Required for replacing the cylinder 5 fuel injector, as the intake manifold must be removed 🎬 See this walkthrough for replacing injectors on the 3.6L engine. for access. These are single-use gaskets and must be replaced to prevent vacuum leaks.
  Trusted brands: ACDelco, Fel-Pro, Mahle
  OEM price range: $40-$70
  Aftermarket price range: $20-$40
• Fuel Injector Connector Pigtail (OEM #13585316 (ACDelco PT2782)) — Needed if the electrical connector itself is damaged, corroded, or broken during diagnosis. This is a common repair when the harness is found to be intact but the connector end is faulty.
  Trusted brands: ACDelco, Dorman
  OEM price range: $20-$40
  Aftermarket price range: $10-$25

Related Codes That Often Appear With This One

• P0305 — This code means 'Cylinder 5 Misfire Detected.' It is a direct result of the P0274 fault, as the injector circuit problem prevents proper fueling of the cylinder, causing a misfire.
• P0273, P0275 — These are circuit low and circuit range/performance codes for the same injector. They can appear if the electrical fault is intermittent or changes characteristics.
• P0087, P0089 — These codes indicate low fuel rail pressure or a regulator performance issue. A stuck-open or leaking injector from an electrical fault can sometimes contribute to these codes appearing simultaneously.

Technical Service Bulletins (TSBs) & Recalls

• PIP4924D: Advises technicians to inspect the fuel injector wiring harness for rub-through or damage when encountering a range of injector circuit codes, including P0274. Specific inspection points are against the intake plenum, valve cover bolts, fuel lines, and the side of the head.

Platform-Specific Known Issues

• A known issue documented in TSB #PIP4924D involves the fuel injector wiring harness rubbing through against engine components, causing shorts or open circuits that trigger various injector codes, including P0274.
• Accessing the rear bank of cylinders (1, 3, 5) is labor-intensive due to the need to remove the upper intake manifold. This adds significant time and cost to the repair if the injector itself needs replacement.

Mechanic-Grade Diagnostic Values

• Fuel Injector Coil Resistance — expected: 1.2 - 1.8 Ohms. Failure: A reading of infinity (OL) for an open circuit, near zero for a shorted circuit, or any value significantly outside the expected range.
• High-Pressure Fuel System (at idle) — expected: Approx. 290 - 798 PSI (2,000 - 5,500 kPa). Failure: Pressure that is significantly low or does not increase with engine load can indicate a failing high-pressure fuel pump (HPFP).
• Low-Pressure Fuel System (engine off, pump commanded on) — expected: 50 - 60 PSI (345 - 414 kPa). Failure: Pressure below 50 PSI suggests a weak in-tank fuel pump or clogged filter.
• Injector Pulse Width (at idle, via scan tool) — expected: 2 - 4 milliseconds (ms). Failure: A value of 0 ms for cylinder 5 while other cylinders show normal values indicates the PCM is not commanding the injector to fire.

Scan Tool Commands That Help

• GDS2 (GM Dealer Software) or equivalent high-end bidirectional scanner: Fuel Injector Balance Test / Active Fuel Injector Tester (AFIT) — This function commands each injector to fire for a set period while monitoring the fuel rail pressure drop. It can identify a mechanically sticking or partially clogged injector that may not have an electrical fault but is still causing a performance issue. GM specifies a variance of no more than 20% between injectors.

Wiring & Ground Locations

• G112 — Rear of the engine, mounted to the rear of the cylinder head (Bank 1).. This is a primary ground point for components on the rear cylinder bank, which includes cylinder 5. A poor or corroded connection at G112 could potentially cause erratic voltage readings and contribute to circuit high codes for injectors on this bank.
• Injector Connector Pin 1 (Control) — At the fuel injector connector for cylinder 5.. This is the control wire from the PCM. A short-to-voltage on this wire will cause a P0274. It should be tested for any voltage with the key on, engine off (it should have none) and for continuity back to the PCM.
• Injector Connector Pin 2 (Power) — At the fuel injector connector for cylinder 5.. This wire supplies power to the injector. It should have battery voltage with the key on. A lack of voltage points to an issue upstream from the injector.

OEM Part Supersession History

• 12638530 → 12669384 — Standard part update and revision by the manufacturer.
  Heads up: While a direct replacement, it is strongly recommended to replace all injectors on the same bank (or all six) at the same time. Mixing original and superseded parts, or OEM and aftermarket parts, can lead to slight differences in fuel flow and atomization, potentially causing subtle performance imbalances.

Model Year Variations Within This Range

• 2009-2011: These model years are typically equipped with the 3.6L LLT V6 engine. This earlier direct-injection engine was known for having issues with timing chain stretch, which is unrelated to P0274 but a significant reliability concern for the engine as a whole.
• 2012-2014: These model years are typically equipped with the updated 3.6L LFX V6 engine. The LFX featured design improvements that resolved the timing chain issues of the LLT and is generally considered a more reliable engine. While the P0274 fault causes and diagnostics remain the same (especially the TSB regarding the wiring harness), the overall engine is a superior design.