P0205 on 2009-2014 GMC Acadia: Cylinder 5 Injector Circuit Fault Causes and Fixes

What's Unique About the 2009-2014 Gmc ACADIA

The 2009-2014 GMC Acadia, equipped with the 3.6L V6 engine, is part of the GM Lambda platform. A Technical Service Bulletin (TSB #PIP4924D) was issued for these vehicles, which includes the P0205 code among a long list of other injector circuit faults. This TSB specifically advises technicians to carefully inspect the fuel injector wiring harness for chafing or internal breaks at several common points: against the intake plenum, at valve cover bolts, against the fuel line, and on the side of the cylinder head. This suggests a higher-than-average likelihood of wiring harness problems being the root cause, rather than just an isolated injector failure.

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 misfire, which may be felt as a shudder or stumble
• Reduced engine power and poor acceleration
• Decreased fuel economy
• Engine may stall
• Hard starting condition
• Vehicle may enter 'limp mode'

Most Likely Causes

1. Faulty Cylinder 5 Fuel Injector 🔴 High Probability → Shop Fuel Injector Injectors can fail electrically over time due to internal coil windings breaking down. This is a common failure item on many vehicles, especially those with over 80,000 miles. The heat and vibration of the engine contribute to this wear.
   How to confirm: Measure the resistance across the injector's two terminals using a multimeter. Compare the reading to the manufacturer's specification (typically 11-14 Ohms for 2009-2011 LLT engines, 1.5-2.5 Ohms for 2012-2014 LFX engines). An open circuit (infinite resistance) or a reading far out of spec indicates a bad injector. Another method is to swap the cylinder 5 injector with an adjacent one (e.g., cylinder 3). If the code changes to P0203, the injector is confirmed faulty.
   Typical fix: Replace the cylinder 5 fuel injector. It is often recommended to replace all injectors on the same bank or the entire set if they are high mileage to ensure balanced performance.
   Est. part cost: $50-$155
2. Wiring Harness or Connector Issue 🔴 High Probability As highlighted by TSB #PIP4924D, these vehicles have known chafe points for the injector harness. Engine vibration and heat can cause wires to rub against the intake plenum, valve cover bolts, or fuel lines, eventually causing a short or open circuit. The connector itself can also suffer from corrosion or loose pin tension.
   How to confirm: Visually inspect the wiring harness leading to the cylinder 5 injector for any signs of damage, chafing, or melting, paying close attention to the areas mentioned in TSB #PIP4924D. Check the connector for corrosion or loose pins. Perform a 'wiggle test' by gently moving the harness while the engine is idling to see if it affects the misfire. Use a multimeter to check for continuity on the control and power wires between the ECM and the injector connector.
   Typical fix: Repair the damaged section of the wiring harness or clean/replace the electrical connector. In some cases, replacing the entire injector harness pigtail is necessary.
   Est. part cost: $10-$50
3. Faulty Engine Control Module (ECM) ⚪ Low Probability → Shop Engine Control Module (ECM)
   How to confirm: This should be the last step after confirming the injector and wiring are both in good condition. A specialized scan tool may be needed to test the injector driver circuit within the ECM. This is a rare failure and should be confirmed by a professional.
   Typical fix: Replace and reprogram the Engine Control Module.
   Est. part cost: $600-$900

Diagnosis Steps

1. Verify the code with an OBD-II scanner and check for any other codes, particularly P0305.
2. Locate cylinder #5 on the 3.6L V6 engine. On the transversely mounted engine in the Acadia, the rear bank (closer to the firewall) contains cylinders 1, 3, and 5, from the passenger side to the driver's side. Cylinder 5 is closest to the driver's side against the firewall.
3. Visually inspect the wiring harness and connector for the cylinder 5 fuel injector. Look for obvious signs of damage, corrosion, or loose connections. Pay special attention to known chafe points mentioned in TSB #PIP4924D.
4. Disconnect the injector and use a multimeter to measure its internal resistance. A typical reading for a 2009-2011 LLT engine is 11-14 Ohms; for a 2012-2014 LFX engine, it is 1.5-2.5 Ohms. An open or shorted reading confirms a bad injector.
5. Use a 'noid light' plugged into the injector's electrical connector. Crank the engine and observe the light. A steady, flashing light indicates the ECM and wiring are sending the pulse signal correctly, pointing to a bad injector.
6. If the noid light does not flash, check for battery voltage at one of the pins on the connector with the key in the 'ON' position.
7. If power is present but the noid light doesn't flash, check the control wire for continuity between the injector connector and the ECM. Repair any open or shorted wires.
8. As a definitive test, consider swapping the cylinder 5 injector with another cylinder's injector (e.g., cylinder 3). Clear the codes and run the engine. If the code changes to P0203, the injector is faulty. If the P0205 code returns, the problem is in the wiring or ECM.
9. If the injector and wiring have been confirmed to be good, the issue may lie with the ECM's injector driver, which is the least likely cause and should be diagnosed by a professional.

Parts You'll Likely Need

• Fuel Injector (OEM #12638530) — This is the most common part to fail internally, causing an electrical fault in the circuit. The original part number 12638530 has been superseded by GM part number 12669384.
  Trusted brands: ACDelco (OEM), Bosch, Standard Motor Products
  OEM price range: $85-$155
  Aftermarket price range: $50-$120
• Upper Intake Manifold Gaskets — The upper intake manifold must be removed to access the fuel injectors on the 3.6L V6. The gaskets are single-use and must be replaced to prevent vacuum leaks.
  Trusted brands: Fel-Pro, ACDelco, Mahle
  OEM price range: $25-$40
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• P0305 — This code means 'Cylinder 5 Misfire Detected.' It is almost always present with P0205 because the injector circuit fault prevents proper fueling, directly causing the cylinder to misfire.
• P0201, P0202, P0203, P0204, P0206 — The presence of multiple injector circuit codes alongside P0205 strongly suggests a wiring harness issue, a shared power supply problem, or a ground fault, as mentioned in TSB #PIP4924D.

Technical Service Bulletins (TSBs) & Recalls

• PIP4924D: Addresses a Service Engine Soon lamp with misfires and various injector DTCs (P0201-P0206, etc.). Recommends inspecting the fuel injector wiring harness for rubbing or open wires against the intake, valve covers, and fuel lines.

Platform-Specific Known Issues

• A known issue documented in Technical Service Bulletin #PIP4924D involves misfires and various injector circuit DTCs (including P0205) on 2009-2014 Acadias. This TSB specifically points to the injector wiring harness chafing against engine components like the intake plenum or valve cover bolts.
• Accessing the rear bank of injectors (including cylinder 5) requires the removal of the upper intake manifold, which adds significant labor time and cost to the repair compared to injectors on the front bank.

Mechanic-Grade Diagnostic Values

• Fuel Injector Coil Resistance (2009-2011 3.6L LLT Engine) — expected: 11 - 14 Ohms. Failure: A reading of 'OL' (open), near zero (short), or significantly outside this range.
• Fuel Injector Coil Resistance (2012-2014 3.6L LFX Engine) — expected: 1.5 - 2.5 Ohms. Failure: A reading of 'OL' (open), near zero (short), or significantly outside this range.
• Injector Connector Voltage (Key On, Engine Off) — expected: ~12 Volts (Battery Voltage). Failure: Low or no voltage on the power supply pin indicates a fault in the power feed circuit, not the injector or control wire.
• Injector Control Voltage (Boost Phase) — expected: ~65 Volts (briefly, requires oscilloscope). Failure: Absence of this initial high-voltage kick can indicate an ECM driver issue.

Hidden / Shadow Codes Worth Checking

• Injector Circuit Test Status: This is not a DTC, but a live data parameter on professional scan tools. It displays 'OK', 'Not Run', or 'Fault' for each injector circuit. It is invaluable for diagnosing intermittent issues by wiggling the harness and watching for the status to change to 'Fault'. (see via GM GDS2/Tech2 or equivalent high-end aftermarket scan tool.)

Scan Tool Commands That Help

• GDS2 / High-End Aftermarket: Fuel Injector Balance Test (AFIT) — Use this after confirming wiring integrity. The tool commands each injector to fire individually and measures the drop in fuel rail pressure. An injector with a pressure drop significantly different from the others is likely faulty or clogged, confirming a component failure without swapping parts.
• GDS2 / Bidirectional Scanner: Cylinder Power Balance / Injector Kill — While the engine is running, this command deactivates one injector at a time. If disabling cylinder 5 causes no change in how the engine runs, it confirms that cylinder was not contributing in the first place, pointing to a problem in that circuit.

Wiring & Ground Locations

• ECM Connector J2, Pin 49 — The ECM is located in the engine compartment, at the front of the engine. The cylinder 5 injector control wire is found on the J2 connector at pin 49.. This is the specific control wire (Light Green/White) for the cylinder 5 injector. Testing for a pulse signal or continuity at this pin can definitively isolate a wiring fault from an ECM fault.
• Ground G113 — Located on the left side of the engine (rear, firewall side) at an engine-to-transmission stud.. This is a primary ground point for Bank 1 (cylinders 1, 3, 5) ignition and fuel components. A loose or corroded connection here can cause intermittent and difficult-to-diagnose electrical faults for the entire bank, including the P0205 code.

Real Owner Repair Stories

• YouTube channel 'P0205 - VZ Commodore 3.6L Injector Control Circuit Malfunction' (Holden Commodore with a 3.6L V6 (similar engine family)) — Dead misfire with DTC P0205 that returned instantly after clearing.
  ❌ Tried (didn't work) The technician skipped a physical resistance test on the injector because it required plenum removal.
  ✅ What actually fixed it The technician used an oscilloscope at the PCM connector and found no command signal being sent on the cylinder 5 injector control wire. The wiring from the PCM to the injector was confirmed good. The final diagnosis was a failed injector driver inside the PCM. Replacing and reprogramming the PCM, along with a new set of injectors as a precaution, resolved the issue.

When the Usual Fixes Don't Work

• While a faulty injector is a high-probability cause, the TSB regarding wiring harness chafe means the harness should always be inspected first on this platform. Furthermore, in cases where both the injector and wiring test good, a failed injector driver within the ECM is a known, albeit rare, cause. A video of a similar 3.6L engine with P0205 documented this exact scenario, where the final fix was a new ECM after confirming no pulse was being sent from the module.

OEM Part Supersession History

• 12638530 (for LLT engine) → 12669384 — Likely for design improvements, reliability updates, or manufacturing changes.
  Heads up: The full supersession chain is 12611545 -> 12632255 -> 12638530 -> 12669384. These parts are for the LLT engine (approx. 2009-2011). They are NOT compatible with the LFX engine (approx. 2012-2014), which uses a different injector with a much lower electrical resistance.

Model Year Variations Within This Range

• 2009-2011 (LLT Engine): These models use fuel injector part number 12638530 (or its supersessions) which has an expected resistance of 11-14 Ohms. They are typically equipped with a Bosch ECM.
• 2012-2014 (LFX Engine): These models may use the updated LFX engine, which features different fuel injectors with a much lower resistance of 1.5-2.5 Ohms. Using the resistance specification from an LLT engine to test an LFX injector would lead to an incorrect diagnosis. These engines often use a Delphi ECM.