P0273 on 2009-2011 Cadillac STS: Cylinder 5 Injector Circuit Low Causes and Fixes

What's Unique About the 2009-2011 Cadillac STS

For this generation of Cadillac STS and many other contemporary GM vehicles with the 3.6L V6 engine, a key vulnerability is the fuel injector wiring harness. GM issued a Technical Service Bulletin (PIP4924D) specifically mentioning that the harness can rub through against the intake plenum, valve cover bolts, fuel lines, or the side of the cylinder head. This known issue makes a thorough wiring inspection a critical first step, often before suspecting the injector itself.

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 shaky idle
• Engine misfire, which may be felt as a shudder or heard as a popping sound
• Hesitation or loss of power during acceleration
• Reduced fuel economy
• Engine may be hard to start or stall

Most Likely Causes

1. Chafed/Damaged Fuel Injector Wiring Harness 🔴 High Probability → Shop Engine Wiring Harness As documented in GM TSB #PIP4924D, the fuel injector wiring harness is known to rub against engine components, causing wires to short to ground or break. Engine movement during operation contributes to this wear over time. Specific chafe points mentioned are against the intake plenum, at valve cover bolts, against the fuel line, and on the side of the head under the plenum.
   How to confirm: Visually inspect the entire length of the fuel injector harness, especially in the areas noted in the TSB. Look for signs of rubbing, exposed copper wires, or melted insulation. Wiggle the harness with the engine running to see if the misfire changes. A video for a related Cadillac CTS shows how to access and inspect the harness. 🎬 Watch this video to see common harness rub points and access.
   Typical fix: Repair the damaged section of wire using a quality butt connector with heat shrink. If the damage is extensive or near the connector, replace the connector pigtail. Protect the repaired area with anti-abrasion tape or loom to prevent recurrence. 🎬 See how to properly solder and shrink-wrap your harness repair.
   Est. part cost: $15-$50 for a repair pigtail
2. Faulty Cylinder 5 Fuel Injector 🟡 Medium Probability → Shop Fuel Injector Direct injection injectors operate under high pressure and can fail internally over time, leading to electrical faults like a short circuit.
   How to confirm: Listen to the injector with a mechanic's stethoscope; it should have a regular, audible clicking sound. You can also measure the injector's resistance with a multimeter and compare it to the other injectors (high impedance injectors are typically around 12 Ohms). The most definitive test is to swap the cylinder 5 injector with another cylinder (e.g., cylinder 3). Clear the codes and run the engine. If the trouble code follows the injector (e.g., changes to P0267), the injector is faulty.
   Typical fix: Replace the faulty fuel injector. It is often recommended to replace all injectors on that bank, or the entire set, if they are high-mileage.
   Est. part cost: $40-$150 per injector
3. Corroded or Loose Injector Connector ⚪ Low Probability
   How to confirm: Disconnect the electrical connector at the cylinder 5 fuel injector and inspect the pins on both the injector and the connector for corrosion, moisture, or damage. Ensure it clicks securely back into place. A poor connection can cause a low voltage reading.
   Typical fix: Clean the connector pins with electrical contact cleaner and apply dielectric grease to prevent future moisture intrusion. If the connector is damaged or won't stay secure, replace the connector pigtail.
   Est. part cost: $15-$50

Rare But Worth Checking

• Faulty Engine Control Module (ECM): → Shop Engine Control Module (ECM) This is rare. The ECM contains a driver circuit for each injector. While it can fail, all other possibilities (wiring, injector) must be exhaustively ruled out first. A failed ECM is often misdiagnosed.

Diagnosis Steps

1. Verify the code with a reliable OBD-II scanner.
2. Locate cylinder 5. On the 3.6L V6 (longitudinal mounting), the passenger side bank is cylinders 1-3-5 (front to back). The driver's side is 2-4-6. On the 4.6L V8 (longitudinal), the passenger side is 1-3-5-7 (front to back) and the driver's side is 2-4-6-8.
3. Visually inspect the fuel injector wiring harness for any signs of chafing, melting, or damage. Pay close attention to the areas mentioned in TSB #PIP4924D: against the intake plenum, at valve cover bolts, against the fuel line, and on the side of the head under the plenum.
4. Inspect the electrical connector on the cylinder 5 injector for corrosion or loose pins.
5. With the engine running, use a mechanic's stethoscope or a long screwdriver to listen to the cylinder 5 injector. It should make a steady clicking noise. Compare the sound to an adjacent injector.
6. If the injector is silent or sounds different, turn off the engine and disconnect the injector. Measure its resistance with a multimeter. It should be around 12-12.5 Ohms. Compare the reading to the other injectors; they should all be very similar.
7. If the injector and wiring appear good, swap the cylinder 5 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 faulty. If the P0273 code returns, the problem is in the wiring or ECM.
8. If the problem persists and the injector is known to be good, perform a continuity test on the injector control circuit wire from the injector connector back to the ECM connector to check for a short to ground.

Parts You'll Likely Need

• Fuel Injector (3.6L V6 LLT) (OEM #12638530) — If the injector itself has an internal short or open circuit, it will cause this code. This is the second most likely failure after a wiring issue.
  Trusted brands: ACDelco, Bosch
  OEM price range: $80-$150
  Aftermarket price range: $40-$90
• Fuel Injector (4.6L V8 LH2) (OEM #12613412 (also listed as 217-3412)) — If the injector has failed on the Northstar V8 engine, this is the correct replacement part. It is a different part than the V6 injector.
  Trusted brands: ACDelco
  OEM price range: $60-$100
  Aftermarket price range: $35-$70
• Fuel Injector Connector Pigtail (OEM #12102568 (GM Interchange)) — Often the wiring damage occurs right at the connector, or the connector itself becomes brittle and fails. Splicing in a new pigtail is the standard repair.
  Trusted brands: ACDelco (PT285), Dorman (85139)
  OEM price range: $25-$50
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• P0305 — P0305 means 'Cylinder 5 Misfire Detected.' Since P0273 indicates a problem with the fuel injector circuit for cylinder 5, that cylinder is not getting the correct amount of fuel, which directly causes a misfire.
• P0205 — P0205 is a more generic 'Injector Circuit/Open - Cylinder 5' code. It often appears alongside P0273 as they both point to an electrical fault in the same circuit.
• P0201, P0202, P0203, P0204, P0206 — If other injector circuit codes appear simultaneously, it strongly suggests a larger wiring harness issue affecting multiple cylinders, rather than a single faulty injector.

Technical Service Bulletins (TSBs) & Recalls

• PIP4924D: Titled 'SES Light And Misfire With Injector Codes,' this bulletin lists a wide range of GM vehicles, including the 2009-2011 STS with 3.6L V6, that are prone to various injector circuit codes (P0273 included) due to the fuel injector wiring harness rubbing through on the engine. It advises technicians to 'Carefully inspect the fuel injector wiring harness for rub through or internal wire opens.'

Platform-Specific Known Issues

• A known issue documented in GM Technical Service Bulletin #PIP4924D involves the fuel injector wiring harness rubbing through, which can cause P0273 and other related injector codes. The bulletin specifically advises inspecting the harness for chafing against the intake plenum, valve cover bolts, fuel lines, and the side of the cylinder head.

Mechanic-Grade Diagnostic Values

• Fuel Injector Coil Resistance (3.6L LLT Direct Injector) — expected: 1.9-2.3 Ohms at 20°C (68°F). Failure: A reading outside this range indicates a faulty injector coil. Resistance changes with temperature.
• Fuel Injector Coil Resistance (4.6L LH2 Port Injector) — expected: ~12 Ohms. Failure: A significant deviation from ~12 Ohms, or a reading that is very different from the other injectors, points to a bad injector.
• Injector Connector Voltage (Key On, Engine Off) — expected: Battery Voltage (approx. 11.5V - 12.5V) on the power feed wire.. Failure: Voltage below 10V suggests a problem in the power supply circuit, such as a corroded wire or faulty fuse.
• Injector Control Circuit Voltage (Lab Scope) — expected: The ECM uses a 65V boost to open the injector, followed by a 12V hold. A lab scope will show this complex waveform.. Failure: Absence of the 65V peak or the 12V hold pattern indicates a fault in the ECM driver circuit. A standard multimeter cannot accurately test this.

Scan Tool Commands That Help

• GDS2 (GM Dealer Scan Tool): Fuel Injector Balance Test — This automated test commands the ECM to fire each injector individually while monitoring the fuel rail pressure drop. It can identify a weak or clogged injector that may not have a hard electrical fault. The GDS2 test for GDI engines measures the pressure drop after hitting a target of ~2072 PSI.
• Tech 2 / Professional Scan Tools: Injector Balance Test (for Port Injection, e.g. 4.6L V8) — For port-injected engines, this test pulses each injector for a set time and the technician records the pressure drop on a mechanical gauge. All injectors should have a pressure drop within 1.5 PSI of each other.

Wiring & Ground Locations

• ECM Connector X1, Pin 47 — On the Engine Control Module (ECM). For the 3.6L V6, the ECM is on the front of the right (passenger side) valve cover.. This is the specific control circuit pin for the cylinder 5 fuel injector. A continuity test from this pin to the injector connector will verify the integrity of the control wire. A wiring diagram for a similar GM engine shows this as a Tan/White wire.
• G106 / G131 — G106 is on the right rear of the engine. G131 is on the left rear of the engine. These are primary engine block grounds.. While P0273 is a circuit-specific code, a poor engine ground can cause widespread, intermittent electrical issues and incorrect voltage readings across multiple sensors and actuators, including the injector circuits. Ensuring these grounds are clean and tight is a crucial step in diagnosing any electrical fault.
• G200 — Inside the passenger compartment, behind the left kick panel.. This ground point serves the Data Link Connector (DLC) and Body Control Module (BCM). While not directly tied to the injector circuit, a fault here can cause communication issues with scan tools, complicating diagnosis.

OEM Part Supersession History

• 12638530 → 12669384 — Standard part number update/revision by GM.
  Heads up: The new part number 12669384 is the correct service replacement for the original 12638530 and is fully compatible for the 2009-2011 STS with the 3.6L V6 engine.