P0204 on 2007-2009 Pontiac G6 3.6L: Injector Circuit Malfunction Causes and Fixes

What's Unique About the 2007-2009 Pontiac G6

The key challenge on the Pontiac G6 with the 3.6L V6 engine is the location of cylinder 4. It is the middle cylinder on the rear bank (firewall side), tucked against the firewall. Accessing the injector or its wiring requires the complete removal of the upper intake manifold, which significantly increases the labor time, cost, and DIY difficulty compared to the same repair on the front bank of cylinders (1, 3, 5).

Symptoms You May Notice

• Check Engine Light is on
• Rough or shaking engine idle
• Noticeable loss of power and poor acceleration
• Engine hesitation or stumbling
• Reduced fuel economy
• A smell of raw fuel in some cases

Most Likely Causes

1. Failed Cylinder 4 Fuel Injector 🔴 High Probability The rear bank of cylinders runs hotter, which can contribute to the electrical failure of components over time. The internal solenoid coil winding inside the injector can fail, creating an open or short circuit.
   How to confirm: After accessing the injector, disconnect it and measure its resistance with a multimeter. A healthy LY7 injector should read between 11 and 14 Ohms. A reading of infinity (open) or zero (short) confirms failure. This is the most definitive test. 🎬 Watch: How to diagnose a fuel injector circuit malfunction.
   Typical fix: Replace the fuel injector for cylinder 4. Since the intake manifold must be removed, it is strongly recommended to also replace the intake manifold gaskets. Many technicians also suggest replacing all three rear injectors (2, 4, 6) at the same time to prevent repeat labor.
   Est. part cost: $70-$120 for a single OEM injector.
2. Wiring Harness Damage 🟡 Medium Probability The engine wiring harness can become brittle from heat cycles and rub against other components, leading to chafed or broken wires. This is a known issue on this platform, with GM issuing TSBs for similar issues on other models. Chafe points can occur where the harness is routed against engine brackets or the corners of the cylinder heads.
   How to confirm: Visually inspect the wiring harness leading to the cylinder 4 injector for any signs of melting, chafing, or breaks. This may require removing the protective loom. Perform a continuity test on the power and signal wires from the PCM connector to the injector connector. 🎬 Watch: How to fix injector codes on GM vehicles.
   Typical fix: Repair the specific damaged section of wire and protect it with loom or electrical tape to prevent future damage.
   Est. part cost: $5-$25 for wiring repair supplies.
3. Bad Injector Connector ⚪ Low Probability Engine vibration can cause micro-movements between the connector terminals and the injector pins. This can lead to 'fretting corrosion,' which appears as a black powder and creates high resistance, causing an intermittent open circuit. GM has issued bulletins regarding fretting corrosion on various connectors.
   How to confirm: Visually inspect the inside of the injector connector for corrosion, backed-out pins, or a powdery black residue. With the connector plugged in, wiggle it while the engine is running to see if the misfire changes.
   Typical fix: Replace the injector connector pigtail, which involves cutting the old connector off and splicing the new one in. The ACDelco pigtail is part number PT2160 (GM #88988313).
   Est. part cost: $25-$45 for a new pigtail connector.

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): This is the least likely cause. The internal driver circuit for the cylinder 4 injector can fail. This should only be considered after the injector, wiring, and connector have all been confirmed to be good.

Diagnosis Steps

1. Verify the code P0204 is present using an OBD-II scanner.
2. Gain access to the rear fuel rail and cylinder 4 injector by removing the upper intake manifold. This is a complex step detailed in many online repair forums.
🎬 See this walkthrough for removing the intake and injectors.
3. Visually inspect the wiring harness and connector for cylinder 4. Look for any obvious signs of damage, melting, chafing, or corrosion. Pay close attention to where the harness may rub against brackets or the engine itself.
4. Disconnect the injector connector. Use a 'noid light' to test for a pulse signal from the PCM while cranking the engine. If the light flashes, the PCM and wiring are likely good. If it's off or stays on solid, there is a wiring or PCM issue.
5. If the noid light test passes, test the fuel injector itself. Set a multimeter to Ohms (Ω) and measure the resistance between the two terminals on the injector. A good injector will read between 11-14 Ohms. An out-of-spec reading (infinity or zero) means the injector has failed.
6. If the noid light test fails, check for 12V power on one of the wires in the connector with the key on (typically the Pink/Black wire on this harness). Then, check the continuity of the other wire (the signal/ground wire, typically Light Blue/Black) back to the PCM connector.
7. If wiring and the injector are good, the final possibility is a faulty injector driver in the PCM.

Parts You'll Likely Need

• Fuel Injector (OEM #12638530) — This is the most common component to fail for this code due to internal electrical failure. The original part number was 217-3034 (GM #12592648), which has been superseded multiple times to #12609418 and most recently to #12638530.
  Trusted brands: ACDelco (GM Original Equipment), Bosch, Delphi, Standard Motor Products
  OEM price range: $70-$120
  Aftermarket price range: $30-$80
• Upper and Lower Intake Manifold Gasket Set (OEM #Fel-Pro MS 96976) — These gaskets are single-use and MUST be replaced anytime the intake manifold is removed to access the rear injectors. Reusing them will cause a vacuum leak. Fel-Pro is a highly recommended aftermarket brand for this application.
  Trusted brands: ACDelco, Fel-Pro, Mahle, Victor Reinz
  OEM price range: $40-$70
  Aftermarket price range: $25-$50

Related Codes That Often Appear With This One

• P0304 — P0304 means 'Cylinder 4 Misfire'. Since the P0204 code indicates the cylinder 4 injector isn't firing correctly, the cylinder will misfire as a direct result.
• P0300 — This indicates 'Random/Multiple Cylinder Misfire'. While P0204 is specific to cylinder 4, a severe issue or accompanying vacuum leak from bad intake gaskets could potentially cause instability that the PCM interprets as misfires on other cylinders.
• P0202, P0206 — If codes for other rear-bank injectors appear simultaneously, it strongly suggests a wiring harness issue common to all three, such as a chafe point or a problem with a shared power or ground circuit.

Technical Service Bulletins (TSBs) & Recalls

• While no TSB is specific to P0204 on the G6, related bulletins for other GM vehicles with similar engines (like TSB #PIP4924D and #21-NA-149) point to wiring harness chafing as a common cause for injector circuit codes, reinforcing the need to inspect wiring thoroughly.
• GM TSB #12-06-01-009D addresses the widespread timing chain issues on the LY7 engine, which is a major known issue for this platform, though not a direct cause of P0204.

Platform-Specific Known Issues

• The LY7 V6 engine family is known for stretched timing chains, but this typically triggers codes like P0008, P0017, and P0300, not a specific injector circuit code like P0204.
• GM does not endorse routine fuel injector cleaning as preventative maintenance, but does recommend using Top Tier detergent gasoline and adding GM Fuel System Treatment PLUS at each oil change to prevent deposit buildup.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 11 - 14 Ohms. Failure: A reading of infinity (OL) indicates an open coil; a reading near zero indicates a shorted coil.
• Fuel Pressure (Key On, Engine Off) — expected: 50 - 60 PSI. Failure: Pressure below 50 PSI indicates a fuel delivery issue (pump, filter), though this would typically affect more than one cylinder.
• Injector Connector Power Pin Voltage (Key On, Engine Off) — expected: 12V (Battery Voltage). Failure: Low or no voltage indicates a problem in the power supply wire or the INJ/COIL fuse.
• Injector Pulse Signal (via Noid Light) — expected: A steady, flashing light while cranking the engine.. Failure: No light, or a light that stays on solid, points to a problem with the wiring or the PCM's injector driver.

Scan Tool Commands That Help

• GM Tech 2 / GDS2: Fuel Injector Balance Test — This test individually fires each injector while monitoring fuel pressure drop. If the pressure drop for cylinder 4 is significantly different from the others (spec is within 3 PSI), it can indicate a clogged or partially functioning injector, even if it passes a basic resistance test.
• GM Tech 2 / GDS2: Cylinder Power Balance — This function disables one cylinder at a time. If disabling cylinder 4 results in little or no change to engine RPM or smoothness, it confirms that cylinder was not contributing power, which is the expected result of a P0204 fault.

Wiring & Ground Locations

• G105 — On the left rear side of the engine compartment, located on an engine-to-transmission stud, below the upper coolant hose.. This is a primary ground point for the engine and transmission assembly. A poor, loose, or corroded connection here can cause erratic voltage and unpredictable behavior from the PCM and its sensor readings, potentially leading to false injector circuit codes.
• Injector Harness Connector — Under the upper intake manifold, plugged directly into the fuel injector for cylinder 4 (rear bank, middle cylinder).. This connector is a common failure point. Constant engine vibration can cause fretting corrosion (seen as black dust) on the terminals, creating high resistance and an intermittent open circuit. The locking tab can also become brittle and break.
• INJ/COIL EVEN Fuse 44 — In the underhood fuse block.. This 15A fuse supplies power to the injectors on the even-numbered bank (2, 4, 6). While a blown fuse would cause all three injectors to lose power (triggering P0202, P0204, and P0206), it should be checked as part of the diagnostic process.

Real Owner Repair Stories

• YouTube user report on a 6.7L Powerstroke, demonstrating a common diagnostic trap. (Ford Truck with 6.7L Powerstroke) — Rough idle, engine missing, P0204 and P1554 codes.
  ❌ Tried (didn't work) Replacing the fuel injector for cylinder 4. The symptoms and codes remained after the new injector was installed.
  ✅ What actually fixed it A continuity test from the PCM connector to the injector connector revealed a broken wire inside the main wiring harness. A new wire was run, bypassing the break, which resolved the issue completely.
• Duramaxtuner.com technical blog post on L5P engines. (GM Truck with L5P Duramax Engine) — P0204, P026D, and P0300 codes, intermittent or dead misfire on cylinder 4.
  ❌ Tried (didn't work) Replacing the #4 fuel injector did not fix the problem.
  ✅ What actually fixed it The issue was traced to the injector pigtail connector. The internal pins had lost tension due to vibration, causing high resistance and an intermittent connection. The fix was to either replace the pigtail or carefully re-crimp the pins to restore proper contact.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Premature Timing Chain Stretch 🔴 High — Extremely common, often occurring between 70,000 and 120,000 miles. Caused by a combination of a weak chain design and long oil change intervals. (Ref: TSB #12-06-01-009D; Special Coverage Adjustment #11340C.)
• Electric Power Steering (EPS) Failure 🔴 High — Common failure of the torque sensor or steering motor, leading to a sudden loss of power assist. Typically occurs around 70,000-100,000 miles. (Ref: GM Recalls #14V153, #14772, #N140115.)
• Transmission Shift Cable Failure (4-Speed Auto) 🟠 Medium — The tabs on the shift cable end can fracture, causing a mismatch between the gear selector position and the actual transmission gear. This can lead to a rollaway risk. (Ref: GM Recall #12V452000.)
• BCM Connector Fretting Corrosion 🟡 Low — Poor terminal contact at the Body Control Module (BCM) connectors can cause various strange electrical issues, such as inoperative taillights or dash warnings. (Ref: No specific recall, but a known pattern failure. The fix often involves cleaning the connectors and applying a special low-voltage dielectric grease.)
• Transmission Wave Plate Failure (6-Speed 6T70/6T75 Auto) 🔴 High — While not as common as timing chains, the 6-speed automatic transmission used with the 3.6L V6 is known for an internal wave plate failure that can cause loss of 3rd, 5th, and reverse gears. (Ref: TSB #14-07-30-001 (for other GM models, but same transmission).)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this repair, using a used fuel injector from a junkyard is NOT recommended. The labor to remove the intake manifold is significant, and the risk of installing a used part with a limited or unknown lifespan is too high. The cost savings do not justify the risk of having to repeat the entire job.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• If forced to use a used part, source it from a vehicle with the lowest possible mileage.
• Inspect the electrical connector pins for any signs of corrosion, bending, or black dust (fretting).
• Ensure the plastic body of the injector has no cracks.
• Ask for the injector's resistance to be measured before purchase; it should be within the 11-14 Ohm range.

OEM-only on this vehicle (don't cheap out):

• While not strictly 'OEM-only', using a reputable brand for the fuel injector is critical. Cheap, unbranded injectors have a high failure rate and are a significant gamble given the labor involved.

Aftermarket brands forum-validated for this vehicle:

• ACDelco (Original Equipment)
• Bosch (Often the OEM supplier)
• Delphi
• Fel-Pro (for intake manifold gaskets)

Brands owners have reported issues with on this vehicle:

• Avoid unbranded, no-name injectors from online marketplaces. While the price is tempting, forum discussions are filled with stories of these parts failing quickly, sometimes within weeks of installation.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0300 — Random or multiple cylinder misfire code; often appears alongside P0204 when the injector circuit failure causes the engine to stumble or hesitate.
• P0008 — Engine Position System Performance code related to the LY7's known timing chain stretch issues, which is a common platform-specific failure.
• P0017 — Crankshaft Position - Camshaft Position Correlation code, another common indicator of the timing chain stretch mentioned in TSB #12-06-01-009D.
• P0202 — Injector circuit code for Cylinder 2; often addressed simultaneously with P0204 as technicians recommend replacing all three rear injectors (2, 4, 6) while the intake manifold is removed.
• P0206 — Injector circuit code for Cylinder 6; shares the same rear bank location and heat-related failure risks as the Cylinder 4 injector.

Frequently Asked Questions