P0273 on 2010-2014 Cadillac SRX: Cylinder 5 Injector Circuit Low Causes and Fixes

What's Unique About the 2010-2014 Cadillac SRX

For this generation of Cadillac SRX and other GM vehicles with the 3.0L and 3.6L V6 engines, a key vulnerability is the fuel injector wiring harness. GM issued Technical Service Bulletin #PIP4924D, which specifically calls out that the harness is prone to rubbing through its insulation. Other bulletins like PIT5424 and PI1067 identify additional specific chafe points, such as against the side of the cylinder head under the plenum or on the metal ECM bracket itself. This makes a wiring issue a much higher probability on these vehicles compared to a random failure of 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
• Engine misfire, which may feel like a shake or stumble, especially at idle
• Rough or uneven idle
• Reduced engine power and sluggish acceleration
• Hesitation when pressing the gas pedal
• Decreased fuel economy
• A strong smell of fuel from the exhaust

Most Likely Causes

1. Chafed or Damaged Fuel Injector Wiring Harness 🔴 High Probability → Shop Engine Wiring Harness As documented in GM TSBs #PIP4924D and #PIT5424, the harness routing on these V6 engines makes it susceptible to rubbing against engine components, causing a short to ground.
   How to confirm: Carefully perform a visual and tactile inspection of the entire fuel injector harness. Pay close attention to documented chafe points: where the harness contacts the intake plenum, valve cover bolts, fuel lines, the side of the cylinder head under the plenum, and where the harness passes the metal ECM bracket. Look for worn insulation, exposed copper wires, or pinch points.
   Typical fix: Repair the damaged section of the wire, ensuring it is properly soldered and insulated with heat-shrink tubing. Protect the repaired area with a new wire loom or conduit. Reroute the harness slightly or use zip ties to secure it away from the point of contact to prevent recurrence.
   Est. part cost: $5-$25
2. Faulty Cylinder 5 Fuel Injector 🟡 Medium Probability → Shop Fuel Injector
   How to confirm: After confirming the wiring is intact, test the injector. With a multimeter, check the injector's internal resistance. For the 3.6L LFX engine, it should be between 1.2 and 1.8 ohms; for the 3.0L LF1, it should be around 11-14 ohms. A reading outside this range indicates failure. Alternatively, swap the cylinder 5 injector with an adjacent one (e.g., cylinder 3). Clear the codes and drive. If the code changes to P0267 (Cylinder 3 Injector Circuit Low), the injector is faulty.
   Typical fix: Replace the faulty fuel injector. It is often recommended to replace the O-rings and seals at the same time. Given the labor to access the rear bank, some owners elect to replace all three injectors on that bank simultaneously.
   Est. part cost: $60-$130
3. Dirty or Clogged Fuel Injector ⚪ Low Probability → Shop Fuel Injector
   How to confirm: This is less likely to cause a 'circuit low' code, which is electrical. However, if the injector is not electrically shorted but is performing poorly, a professional fuel injector balance test may identify a flow issue.
   Typical fix: Have the fuel injectors professionally cleaned or replace the single faulty injector.
   Est. part cost: $60-$130

Rare But Worth Checking

• Faulty Engine Control Module (ECM): → Shop Engine Control Module (ECM) This is the least likely cause. The internal driver circuit for cylinder 5 within the ECM can fail. All other possibilities, especially wiring and the injector itself, should be exhaustively ruled out before considering ECM replacement, as it is expensive and requires programming.

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner and note any other codes present, especially P0305.
2. Carefully inspect the fuel injector wiring harness as described in TSBs #PIP4924D and #PIT5424. Look for any signs of rubbing or damage, particularly where the harness runs near the intake manifold, valve covers, the side of the cylinder head, and the ECM bracket.
3. If damage is found, repair the wire, clear the codes, and test drive to see if the code returns.
4. If the wiring appears okay, locate cylinder 5. For the transverse V6 in the SRX, the rear bank (against the firewall) contains cylinders 1-3-5 and the front bank (near the radiator) contains cylinders 2-4-6. Both banks are arranged from the passenger side to the driver side. Cylinder 5 is the rear-most cylinder on the driver's side. Accessing this cylinder requires removing the upper intake manifold.
5. Test the injector's resistance. Disconnect the injector and use a multimeter to measure the resistance across its two pins. Compare your reading to the specification (approx. 1.2-1.8 Ohms for 3.6L, ~11-14 Ohms for 3.0L). If it's out of spec, the injector has failed.
6. As an alternative to resistance testing, swap the cylinder 5 fuel injector with another cylinder's injector (e.g., cylinder 3).
7. Clear the codes and drive the vehicle. If the code returns as P0267 (for cylinder 3), the fuel injector is confirmed to be faulty and must be replaced.
8. If the code P0273 returns after the swap, the problem lies within the wiring or the ECM. Perform a continuity test on the injector's control wire from the injector connector back to the ECM connector to check for opens or shorts to ground.
9. If wiring and the injector are confirmed good, the final possibility is a failed driver circuit in the ECM.

Parts You'll Likely Need

• Fuel Injector (OEM #12629927 (for 3.0L V6), 12634126 (for 3.6L V6)) — This is the part to replace if it fails a resistance or swap test, indicating an internal electrical short.
  Trusted brands: ACDelco, Hitachi, Standard Motor Products
  OEM price range: $100-$130
  Aftermarket price range: $55-$95
• Fuel Injector Wiring Harness Connector (Pigtail) — If the wiring is damaged right at the connector, or the connector itself is corroded or broken, replacing the pigtail is the correct repair.
  Trusted brands: ACDelco, Dorman
  OEM price range: $30-$50
  Aftermarket price range: $15-$30
• Upper Intake Manifold Gasket Set — This is required to be replaced when removing the upper intake manifold to access the rear bank of injectors (including cylinder 5). It is not reusable.
  Trusted brands: ACDelco, Fel-Pro
  OEM price range: $25-$40
  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.
• P0300 — P0300 means 'Random/Multiple Cylinder Misfire Detected'. This can occur if the wiring harness issue is severe enough to intermittently affect other injector circuits in the same bundle.

Technical Service Bulletins (TSBs) & Recalls

• PIP4924D: SES Light And Misfire With Injector Codes - Advises inspection of the fuel injector wiring harness for rub-through or open circuits as a primary diagnostic step for a list of codes including P0273.
• PIT5424: Calls for inspection of the engine harness routing between the ECM and the upper rear of the engine for chafing that can cause various injector circuit codes.
• PI1067: (For 3.6L LFX) Specifically identifies a chafe point where the ECM wiring harness (from connector X1) rubs on the metal ECM bracket, causing wire damage.
• PI0631G: Notes that the engine harness on the 3.6L LFX engine can rub against the transmission case, causing shorts in various circuits.

Platform-Specific Known Issues

• GM Technical Service Bulletin #PIP4924D explicitly warns technicians to inspect the fuel injector wiring harness for rubbing through against engine components before replacing parts.
• Additional bulletins like PIT5424 and PI1067 point to other specific chafe points, including the harness rubbing against the side of the cylinder head or the ECM's own metal mounting bracket, making a thorough harness inspection critical.
• Accessing cylinder 5 (and its injector/wiring) is labor-intensive as it is on the rear bank against the firewall, requiring the removal of the upper intake manifold.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance (3.6L LFX V6) — expected: 1.2 - 1.8 Ohms. Failure: A reading outside this range, OL (open), or near zero Ohms indicates an internal injector fault.
• Fuel Injector Resistance (3.0L LF1 V6) — expected: 11 - 14 Ohms. Failure: A significant deviation from this range, OL (open), or near zero Ohms indicates a fault in the high-impedance injector's coil.
• High-Pressure Fuel Rail (3.6L LFX V6) — expected: 300 - 500 PSI at idle, rising to over 2,000 PSI under load.. Failure: Pressure that is significantly low or does not increase with engine load points to a failing high-pressure fuel pump (HPFP).
• Injector Control Circuit Voltage (Key On, Engine Off) — expected: Battery Voltage (approx. 12.6V) on the power supply wire (Pink wire on many GM models).. Failure: 0V on the power supply wire indicates a blown fuse or power feed issue.

Scan Tool Commands That Help

• GM GDS2 / Tech2: Fuel Injector Balance Test — This bidirectional test functionally checks an injector when electrical tests are inconclusive. The tool commands each injector to fire for a precise duration and measures the corresponding drop in fuel rail pressure. If the pressure drop for cylinder 5 is significantly different from the others, it indicates a malfunctioning (clogged or leaking) injector. This should be performed after verifying wiring integrity.
• GM GDS2 / Tech2: Cylinder Power Balance — This function allows the user to disable one cylinder at a time to see the effect on engine RPM. If disabling cylinder 5 causes little or no change in RPM drop compared to other cylinders, it confirms that cylinder 5 is not contributing power, which supports the P0273 diagnosis.

Wiring & Ground Locations

• Cylinder 5 Injector Control Pin — On the 3.6L LFX, the control wire for the cylinder 5 injector is typically a Tan/White wire that runs to Pin 18 of the X1 (Black or Blue) ECM connector.. This is the specific pin to test for continuity back to the injector connector. A short to ground or an open on this wire will cause P0273.
• G103 / G108 — Typically located on the cowl in the rear of the engine compartment, sometimes near the brake booster.. This is a primary ground point for the Engine Control Module (ECM). A loose or corroded connection here can cause erratic behavior and various engine management codes, including injector circuit faults.
• X160 / X161 Connectors — These are multi-way injector harness connectors located at the rear of the intake manifold.. Disconnecting these allows a technician to isolate the injector bank from the main engine harness to test for shorts or opens, helping to determine if the fault is in the injector-specific harness or the main engine harness.

Real Owner Repair Stories

• Cadillac Forums user (Vehicle similar to SRX with 3.6L engine) — Check engine light with P0305 (Cylinder 5 misfire) and related injector codes.
  ❌ Tried (didn't work) Swapping coils, Swapping spark plugs
  ✅ What actually fixed it The user found the wiring harness had rubbed through on the back of the cylinder head near the firewall. Repairing the damaged wires resolved the codes.

OEM Part Supersession History

• 12642021 → 12629927 — Part number consolidation and updates for the 3.0L LF1 engine.
  Heads up: This part is for the 3.0L LF1 engine (2010-2011) ONLY and is not compatible with the 3.6L LFX engine.
• 12642128 → 12634126 — Part number consolidation and updates for the 3.6L LFX engine.
  Heads up: This part is for the 3.6L LFX engine (2012-2014) ONLY and is not compatible with the 3.0L LF1 engine.

Model Year Variations Within This Range

• 2010-2011: These models use the 3.0L LF1 V6 engine. The correct fuel injector is a high-impedance type (approx. 11-14 Ohms), OEM part number 12629927 (or its equivalent ACDelco 217-3449).
• 2012-2014: These models use the 3.6L LFX V6 engine. The correct fuel injector is a low-impedance type (approx. 1.2-1.8 Ohms), OEM part number 12634126. The parts are not interchangeable between engines.