P0268 on 2009-2011 Cadillac STS: Cylinder 8 Injector Circuit High Causes and Fixes

What's Unique About the 2009-2011 Cadillac STS

On the 2009-2011 Cadillac STS, this code is exclusive to the 4.6L Northstar V8 engine (RPO code LH2), as it's the only engine with eight cylinders. General Motors has issued technical service bulletins for various models regarding fuel injector wiring issues. For this specific vehicle and its platform mates (like the Cadillac DTS), TSB #PIP4924D points directly towards inspecting the fuel injector wiring harness for damage, making it a primary suspect over the injector itself. The LH2 version of the Northstar is considered the most refined and durable of the family, with many earlier issues resolved.

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 stumble or hesitation during acceleration.
• Noticeable loss of power.
• Potentially increased fuel consumption.
• Strong fuel smell from the exhaust if the injector is stuck open.

Most Likely Causes

1. Fuel Injector Wiring Harness Shorted or Damaged 🔴 High Probability → Shop Engine Wiring Harness As cited in GM Technical Service Bulletin #PIP4924D, the fuel injector wiring harness is a known weak point. The harness can chafe against engine components like brackets or the fuel rail, or the insulation can become brittle from heat cycles, leading to a short circuit to a power source. This is a common failure point on many GM vehicles of this era.
   How to confirm: Visually inspect the wiring harness leading to the cylinder 8 fuel injector. Look for any signs of rubbing, melting, exposed wires, or corrosion at the connector. Pay close attention to points where the harness makes contact with metal brackets or the engine itself. Use a multimeter to check for voltage on the control wire with the injector disconnected and the key in the 'on' position. Presence of voltage indicates a short to power.
   Typical fix: Repair the damaged section of the wire or replace the injector connector pigtail. 🎬 See how to properly repair and solder damaged engine harness wiring. Protect the repaired harness from future damage using a high-quality loom or by re-routing it away from sharp edges.
   Est. part cost: $15-$50
2. Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector Fuel injectors can fail internally over time due to heat and mileage, leading to an electrical short. While not as common as wiring issues on this platform, it is a frequent cause of injector circuit codes in general.
   How to confirm: With the engine off, disconnect the injector and measure its internal resistance with a multimeter. Compare the reading to the manufacturer's specification (typically 11-16 ohms for this type). An open circuit (infinite resistance) or a short (very low resistance) indicates a failed injector. A mechanic's stethoscope can be used to listen for a consistent clicking sound from the injector while the engine is running; silence or an erratic click suggests a problem.
   Typical fix: Replace the cylinder 8 fuel injector. It is often recommended to replace the O-rings for any other injectors that are disturbed when the fuel rail is removed.
   Est. part cost: $70-$150
3. Faulty Powertrain Control Module (PCM) ⚪ Low Probability → Shop Engine Control Module (ECM) PCM failure is rare but possible. An internal short in the injector driver circuit within the PCM can cause a P0268 code. This can sometimes happen if an external wiring short or a failed injector damages the module.
   How to confirm: This is diagnosed by exclusion. If the injector and its wiring have been tested and are confirmed to be good, the injector driver circuit within the PCM is the likely culprit. This requires advanced diagnostic tools, like an oscilloscope, to confirm the driver's signal pattern.
   Typical fix: Replace and reprogram the Powertrain Control Module. This must be done by a dealer or a qualified shop with the correct programming tools.
   Est. part cost: $300-$800

Diagnosis Steps

1. Verify the code's presence using an OBD-II scanner. Note any other codes, especially P0308, and freeze frame data.
2. Identify cylinder #8 on the 4.6L Northstar V8. It is the rearmost cylinder on the driver's side (left bank).
3. Perform a thorough visual inspection of the wiring harness and connector for cylinder 8. Following the advice of TSB #PIP4924D, look for chafing against brackets, the fuel rail, or other components. Also check for melted insulation or corrosion.
4. Disconnect the fuel injector. Use a multimeter to check for voltage on the control wire (the one that is not the shared power wire). With the key on, engine off, there should be no voltage. If voltage is present, there is a short to power in the harness.
5. With the injector still disconnected, measure the resistance across the two pins on the injector itself. A reading outside of the 11-16 ohm range indicates a faulty injector.
6. If a noid light is available, plug it into the injector connector and crank the engine. A flashing light indicates the PCM is trying to fire the injector, suggesting the problem is the injector itself. No light or a steady light points to a wiring or PCM issue.
🎬 Watch: How to test for a circuit high code using a multimeter.
7. If the wiring and injector test good, the fault likely lies within the PCM's injector driver circuit. This requires professional diagnosis, often with an oscilloscope to analyze the driver signal.

Parts You'll Likely Need

• Fuel Injector (OEM #12613412) — An internal short in the injector can cause the 'Circuit High' condition. It is the second most likely failure point after the wiring. This part number is for a common GM Flex Fuel injector used in many applications and may be a compatible replacement.
  Trusted brands: ACDelco, Delphi, Bosch
  OEM price range: $120-$180
  Aftermarket price range: $70-$110
• Fuel Injector Connector Pigtail (OEM #ACDelco PT2183 (GM 88988963)) — If the wiring is damaged at the connector, replacing the pigtail is the standard repair. This is a very common fix given the TSB about wiring issues. This is a multi-purpose connector used across many GM vehicles.
  Trusted brands: ACDelco, Dorman
  OEM price range: $25-$40
  Aftermarket price range: $15-$25

Related Codes That Often Appear With This One

• P0308 — P0308 means 'Cylinder 8 Misfire Detected.' This code is a direct result of the P0268 fault, as the disabled injector prevents proper combustion in that cylinder.
• P0208 — P0208 is a more general 'Injector Circuit/Open - Cylinder 8' code. It can appear alongside P0268 if the nature of the electrical fault fluctuates between an open and a short.

Technical Service Bulletins (TSBs) & Recalls

• PIP4924D: Addresses multiple engine diagnostic trouble codes, including P0268, related to engine misfires, advising technicians to inspect the fuel injector wiring harness for damage.

Platform-Specific Known Issues

• Per TSB #PIP4924D, the fuel injector wiring harness is susceptible to damage, which can cause a variety of injector circuit codes, including P0268. Technicians are advised to inspect the harness for chafing on engine components before replacing parts. [⭐ MANUFACTURER TSB — highest authority]
• Owners on forums have noted that the plastic conduit covering the injector harness can become brittle and break, exposing the wires to direct contact with hot or sharp engine parts. A common chafe point is where the harness routes near metal brackets holding other components.

Mechanic-Grade Diagnostic Values

• Fuel Injector Internal Resistance — expected: 11.0 - 16.0 Ohms (specifically 12 Ohms is a common value for this injector type). Failure: A reading significantly outside this range, especially near zero (short) or infinite (open).
• Fuel Pressure (Key On, Engine Off) — expected: 55-60 psi (380-410 kPa). Failure: Pressure significantly below this range could indicate a fuel delivery issue, though it would not typically cause a 'Circuit High' code.
• Injector Control Wire Voltage (Key On, Engine Off, Injector Disconnected) — expected: 0 Volts. Failure: Any significant voltage, especially battery voltage, indicates a short to power in the wiring harness.
• Injector Power Wire Voltage (Key On, Engine Off) — expected: Battery Voltage (approx. 12V). Failure: No voltage indicates a problem with the power supply circuit to the injector bank.

Scan Tool Commands That Help

• GM Tech 2 / GDS2: Fuel Injector Balance Test — This test can help identify a mechanically faulty injector but is less useful for a purely electrical 'Circuit High' fault where the injector is already disabled. The test commands each injector to fire for a precise duration while monitoring fuel pressure drop. A significant deviation in pressure drop for one cylinder points to a flow issue (clogged or leaking). It can be used after a repair to verify injector function.
• GM Tech 2 / GDS2: Cylinder Power Balance — This test disables one cylinder at a time to measure the RPM drop. For P0268, the ECM is already disabling cylinder 8, so running this test and disabling cylinder 8 should result in no change in engine performance, confirming the misfire. Disabling other cylinders should produce a noticeable RPM drop.

Wiring & Ground Locations

• Cylinder 8 Injector Control Wire — Pin 45 on the C2 (73-way) connector of the Engine Control Module (ECM). The wire color is typically Dark Blue/White.. This is the specific wire the ECM uses to ground-switch the cylinder 8 injector. A short to voltage anywhere along this wire will cause a P0268 code. Testing for continuity and shorts should be done on this wire between the ECM and the injector connector.
• G100 / G106 — On the rear side of the right (passenger side) cylinder head.. These are primary engine grounds. While a poor ground is more likely to cause 'Circuit Low' or 'Open' codes, an intermittent or poor ground connection for the ECM can cause a wide range of unpredictable electrical faults, including incorrect voltage readings. Verifying these grounds are clean and tight is a fundamental step.
• ECM Location — On the 4.6L engine, the ECM is located on the left (driver's side) front frame rail, below the headlamp assembly.. Knowing the physical location is necessary for inspecting the main ECM connectors (X1/X2) for corrosion or damage and for performing pinout testing on the injector control wire.
• Injector Harness Routing — The injector harness for Bank 2 (driver's side, cylinders 2-4-6-8) runs along the fuel rail, under the intake manifold cover.. This area is a prime location for chafing. The harness can rub against the fuel rail, intake manifold bolts, or nearby brackets, especially as the plastic loom becomes brittle with age.

Real Owner Repair Stories

• CorvetteForum Discussion (Corvette with GM LS-series V8 (similar wiring architecture)) — Intermittent misfire and injector codes.
  ❌ Tried (didn't work) Initial diagnosis was inconclusive.
  ✅ What actually fixed it The owner located a spot where the injector wiring harness was chafing near the rear of the driver's side cylinder head. Protecting the chafed area with a wire loom resolved the issue permanently.
• PowerStrokeArmy Forum Discussion (Ford Powerstroke Diesel (different vehicle, but illustrates a common wiring failure pattern)) — Sporadic loss of connection to injectors, causing misfires.
  ❌ Tried (didn't work) Replacing the external harness connector did not fix the problem.
  ✅ What actually fixed it The problem was identified as the wiring harness chafing where it comes over the valve cover near the main 42-pin connector. This is a common wear point that is often overlooked.