P0261 on 2009-2014 GMC Acadia: Cylinder 1 Injector Circuit Low Causes and Fixes

What's Unique About the 2009-2014 Gmc ACADIA

The 2009-2014 GMC Acadia and its GM Lambda platform siblings (Buick Enclave, Chevrolet Traverse, Saturn Outlook) use a 3.6L V6 engine with direct injection. While the code itself is generic, these vehicles are known for wiring harness issues where the harness chafes against engine components, leading to shorts. Specific problem areas include the front corner of the left-hand cylinder head and the ECM/TCM bracket. The provided TSB #PIP4924D lists P0261 among a large group of injector codes, suggesting a common electrical failure point that can affect multiple cylinders, often related to wiring or connectors at the rear of the intake manifold.

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 (may be flashing if misfire is severe)
• Rough or shaking idle
• Engine misfire, which may feel like a tapping or stumble
• Hesitation or lack of power during acceleration
• Reduced fuel economy
• Engine may be hard to start

Most Likely Causes

1. Faulty Cylinder 1 Fuel Injector 🔴 High Probability → Shop Fuel Injector Direct injectors operate under high pressure and extreme temperatures. The internal coil windings can fail, causing an electrical short or low resistance that triggers the P0261 code.
   How to confirm: Swap the cylinder 1 fuel injector with another cylinder (e.g., cylinder 3). Clear the codes and run the engine. If the code changes to P0267 (Cylinder 3 Injector Circuit Low), the injector is confirmed faulty.
   Typical fix: Replace the failed fuel injector. It is often recommended to replace all injectors on that bank (Bank 1, the rear bank) or all six at the same time, as they have similar wear. New seals are required.
   Est. part cost: $50-$150 per injector
2. Wiring Harness Damaged or Shorted 🔴 High Probability GM has issued service bulletins for Lambda platform vehicles regarding engine wiring harnesses chafing. Common chafe points are against the corner of the cylinder head, the drive belt idler pulley bracket, and the oil dipstick bracket, causing a short to ground.
   How to confirm: Visually inspect the wiring harness leading to the cylinder 1 injector, especially where it runs near the back of the intake manifold and around brackets. Unplug the harness at the injector and ECM and use a multimeter to check for a short to ground on the control wire.
   Typical fix: Repair the damaged section of the wire using a butt connector with heat shrink. Protect the harness from future chafing using a high-temperature wire loom 🎬 See this guide on how to repair a damaged wiring harness. or by re-routing it away from sharp edges.
   Est. part cost: $10-$50 for repair materials
3. Poor Connection at Injector or ECM 🟡 Medium Probability The connectors, especially the multi-way connectors X160 or X161 at the rear of the intake manifold, are exposed to heat and vibration, which can cause terminals to loosen or corrode.
   How to confirm: Disconnect and inspect the electrical connector at the fuel injector and the corresponding pins at the ECM and the main harness connectors. Look for corrosion (green crust), bent pins, or a loose fit.
   Typical fix: Clean the connector terminals with electrical contact cleaner and apply dielectric grease before reconnecting. If the connector is damaged, replace the pigtail.
   Est. part cost: $15-$40

Rare But Worth Checking

• Faulty Engine Control Module (ECM): → Shop Engine Control Module (ECM) This is rare. The internal driver circuit for the injector can fail, but all other possibilities (injector, wiring, connectors) should be exhaustively tested before condemning the ECM. An ECM failure is more likely if multiple, unrelated codes are present.

Diagnosis Steps

1. Read the codes with an OBD-II scanner to confirm P0261 and note any other codes present, especially P0301 or other injector codes.
2. Inspect the electrical connector on the cylinder 1 fuel injector for damage, corrosion, or a loose fit. Cylinder 1 is on the rear bank (Bank 1), closest to the firewall.
3. Perform a 'screwdriver test': place the tip of a long screwdriver on the body of the injector while the engine is running and listen at the handle. A healthy injector will make a distinct, rhythmic clicking sound. Silence indicates an electrical or mechanical failure.
4. If accessible, swap the cylinder 1 injector with an injector from another cylinder (e.g., cylinder 3, also on the rear bank). Clear the codes and run the engine. If the fault code moves to the new cylinder (e.g., P0267), the injector is bad.
5. If the code remains P0261 after the swap, the issue is in the wiring or ECM. Disconnect the multi-way harness connectors X160 or X161 at the rear of the intake manifold and inspect for damage or corrosion.
6. Inspect the engine wiring harness for any signs of chafing, melting, or breaks. Pay close attention to where the harness may rub against the cylinder head, accessory brackets, or the firewall.
7. Use a multimeter to check the injector circuit. Check for continuity on the wiring between the ECM connector and the injector connector. Then, check for a short to ground on the control wire with the injector and ECM disconnected.
8. If wiring and the injector are confirmed to be good, the final possibility is a fault within the Engine Control Module (ECM), which is rare.

Parts You'll Likely Need

• Fuel Injector (OEM #12638530 (For 2009-2011 LLT Engine, may be superseded by 12669384)) — The internal coil of the direct fuel injector can short out, causing the 'Circuit Low' condition. This is a common failure point. Always verify part number with VIN.
  Trusted brands: ACDelco, Bosch
  OEM price range: $80-$150
  Aftermarket price range: $40-$90
• Fuel Injector Connector Pigtail (OEM #ACDelco PT2183 (verify fitment)) — If the connector itself is corroded or damaged, or if the wires are broken right at the connector, replacing the pigtail is the most effective repair.
  Trusted brands: Dorman, ACDelco
  OEM price range: $25-$40
  Aftermarket price range: $15-$30
• Intake Manifold Gasket Set — Required for injector replacement on the rear bank (Cylinder 1), as the intake manifold must be removed for access. 🎬 Watch: Step-by-step fuel injector and spark plug replacement walkthrough.
  Trusted brands: Fel-Pro, ACDelco
  OEM price range: $40-$70
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• P0301 — P0301 means 'Cylinder 1 Misfire Detected'. This code is a direct and expected result of the P0261 fault, as the injector circuit problem prevents proper fueling, causing the cylinder to misfire.
• P0201, P0264, P0267, etc. — If multiple injector circuit codes are present (e.g., P0261, P0264, P0267 for cylinders 1, 2, 3), it strongly points towards a shared problem like a damaged wiring harness affecting several injector circuits or a failing ECM driver bank, as suggested by TSB PIP4924D.

Technical Service Bulletins (TSBs) & Recalls

• PIP4924D: This bulletin addresses a Service Engine Soon light with a misfire and a wide range of injector circuit DTCs, including P0261. It advises technicians to inspect the fuel injector wiring harness for rubbing through or internal wire opens and to repair or replace the harness as needed.

Platform-Specific Known Issues

• A known issue on GM Lambda platform vehicles is the engine wiring harness rubbing on brackets or the cylinder heads, causing wires to short out. TSB #PIP4924D and others point to this type of failure as a cause for various injector circuit codes. Owners should pay special attention to the harness near the firewall and around the rear of the engine when diagnosing this code.

Mechanic-Grade Diagnostic Values

• Fuel Injector Coil Resistance (2012-2014 LFX Engine) — expected: 1.5 - 2.5 ohms. Failure: A reading near 0 ohms indicates a short; an 'OL' or infinite reading indicates an open circuit.
• Fuel Injector Coil Resistance (2009-2011 LLT Engine) — expected: 11 - 14 ohms. Failure: A reading outside this range indicates a faulty injector coil.
• Injector Connector Voltage (Key On, Engine Off) — expected: ~12 Volts (Battery Voltage). Failure: Voltage significantly below battery voltage points to a wiring issue on the power supply side.
• Injector Control Circuit Ground Resistance — expected: Less than 0.1 Ω. Failure: Values above 0.1 Ω indicate a poor ground connection that needs to be located and cleaned.
• Scan Tool 'Fuel Injector Balance Test' Pressure Drop — expected: The pressure drop for cylinder 1 should be within 1.5 PSI (10 kPa) of the average of all other cylinders.. Failure: A significantly smaller or larger pressure drop for cylinder 1 indicates a flow issue (clogged or leaking).

Scan Tool Commands That Help

• GDS2 (GM Tech 2 successor): Fuel Injector Balance Test — This bidirectional command pulses each injector individually while monitoring fuel rail pressure drop. It is used to confirm if an injector is clogged or flowing less than others, helping to differentiate a flow problem from a purely electrical one after wiring has been checked.
• GDS2 (GM Tech 2 successor): Injector Control Circuit Test Status — While wiggling harnesses and connectors with the engine running, monitoring this parameter can help isolate intermittent faults. The status will change from 'OK' or 'Not Run' to 'Fault' if a connection is momentarily lost or shorted.

Wiring & Ground Locations

• X161 — Multi-way harness connector at the rear of the intake manifold.. This connector contains the wiring for the Bank 1 injectors (including cylinder 1). The Cylinder 1 high voltage supply circuit is on pin 8. It's a common point for corrosion or loose connections affecting the entire bank.
• G110 — Right front of the engine, mounted to the cylinder head.. This is a primary engine ground point. A loose or corroded connection here can cause various electrical issues, including erratic sensor readings and injector circuit problems.
• G113 — Left side of the engine, at an engine-to-transmission stud.. Another critical engine ground. Poor contact at this location can affect the ECM's ground reference, potentially leading to incorrect fault code setting.
• ECM (Engine Control Module) — Located in the left front corner of the engine compartment.. The ECM provides the power and control signal to the fuel injector. All circuit tests ultimately lead back to the ECM connectors to confirm if the fault is in the wiring or the module itself.

Real Owner Repair Stories

• acadiaforum.net user (2008 GMC Acadia) — P0301 (Cylinder 1 Misfire), P0261 (Cylinder 1 Injector Circuit Low), P0300 (Random Misfire)
  ❌ Tried (didn't work) Initial diagnosis pointed towards a bad injector.
  ✅ What actually fixed it The user found a chafed wire in the wiring harness near the firewall. The insulation had worn through, causing the injector control wire to short to ground. Repairing the wire and protecting the harness resolved all codes.

OEM Part Supersession History

• 12638530 → 12669384 — Part was updated by the manufacturer for improved reliability or manufacturing process.
  Heads up: Do not mix original and superseded injectors on the same engine, as flow rates and characteristics may differ slightly. It is recommended to replace them in a full set if upgrading.

Model Year Variations Within This Range

• 2009-2011: These models use the 3.6L LLT V6 engine. This engine has an aluminum intake manifold, a Bosch ECM, and uses fuel injectors with a resistance of 11-14 ohms (PN 12638530 or supersession).
• 2012-2014: These models use the updated 3.6L LFX V6 engine. This engine features a lighter composite intake manifold, integrated exhaust manifolds, a Delphi ECM, and different fuel injectors with a lower resistance of 1.5-2.5 ohms. Parts, especially injectors, are not cross-compatible with the LLT engine.