P0270 on 2009-2014 Buick LaCrosse: Cylinder 4 Injector Circuit Low Causes & Fixes

What's Unique About the 2009-2014 Buick LACROSSE

For this generation of Buick LaCrosse and other GM vehicles with similar engines, the fuel injector wiring harness is a known weak point. A specific Technical Service Bulletin (TSB PIP4924D) was issued because these harnesses are prone to rubbing against engine components like the intake plenum, valve cover bolts, or fuel lines, leading to chafed wires, open circuits, and codes like P0270. This makes a wiring inspection a critical first step, often revealing the problem without needing to replace more expensive parts. The issue is common across the GM Epsilon II platform vehicles sharing these V6 engines.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: This range covers the end of the first-generation LaCrosse (2009, on the W-body platform) and the majority of the second generation (2010-2014, on the Epsilon II platform). The engines varied, including the 2.4L I4, 3.0L V6 (LF1), and 3.6L V6 (LLT/LFX). The primary cause, a faulty fuel injector wiring harness, is a known issue across multiple GM engines from this era, as noted in TSB PIP4924D which covers all these model years and engines.

Symptoms You May Notice

• Check Engine Light is on (may be flashing if misfire is severe)
• Rough or shaky idle
• Engine misfire, which may feel like a stumble or hesitation during acceleration.
• Reduced engine power and performance.
• Poor fuel economy.
• Engine stalling in some cases

Most Likely Causes

1. Fuel Injector Wiring Harness Damaged or Chafed 🔴 High Probability → Shop Engine Wiring Harness As identified in GM TSB #PIP4924D, the harness routing can cause it to rub against the intake plenum, valve cover bolts, fuel lines, or the side of the cylinder head, causing wires to break or short. This constant vibration and contact wears through the wire insulation.
   How to confirm: Visually inspect the entire fuel injector harness, paying close attention to cylinder 4's wiring. On the V6 engines, cylinder 4 is the middle cylinder on the front bank (radiator side). Look for any signs of rubbing, melting, or exposed copper wire. Use a multimeter to check for continuity from the PCM connector to the injector connector. A resistance reading above 0.5-1.0 ohms indicates a wiring problem.
   Typical fix: Repair the damaged section of wire. In many cases, a new connector pigtail is spliced in. If the damage is extensive, the entire injector harness may need replacement. Use anti-abrasion tape or loom to protect the repaired area from future damage.
   Est. part cost: $15-$50 for a connector pigtail.
2. Faulty Cylinder 4 Fuel Injector 🟡 Medium Probability → Shop Fuel Injector Injectors can fail electrically over time due to internal coil windings shorting out or breaking. This is a common failure on many vehicles, not just the LaCrosse.
   How to confirm: After confirming the wiring is good, swap the cylinder 4 fuel injector with one from another cylinder (e.g., cylinder 2). Clear the codes and drive the vehicle. If the code changes to P0264 (Cylinder 2 Injector Circuit Low), the injector is faulty. You can also check the injector's internal resistance with a multimeter; it should be within the manufacturer's specified range (typically 10-18 ohms). A reading far outside this range indicates a failed injector.
   Typical fix: Replace the failed fuel injector. It is often recommended to replace the Teflon seal and retaining clip at the same time. For Direct Injection (V6) models, this is a more involved job. 🎬 See this walkthrough for replacing injectors on a GM 3.6L.
   Est. part cost: $50-$150
3. Dirty or Clogged Fuel Injector ⚪ Low Probability → Shop Fuel Injector
   How to confirm: This is difficult to confirm without specialized flow-testing equipment. A clogged injector typically causes a lean condition or misfire (P0304) but is less likely to cause a specific 'Circuit Low' code unless the blockage causes the injector to work improperly electrically. It's usually diagnosed by eliminating other possibilities.
   Typical fix: Professionally clean the fuel injectors or replace the clogged injector.
   Est. part cost: $50-$150 for a replacement.

Rare But Worth Checking

• Powertrain Control Module (PCM) Failure: → Shop Engine Control Module (ECM) This is the least likely cause. The internal driver circuit for the cylinder 4 injector can fail, but all other possibilities, especially wiring and the injector itself, should be exhaustively ruled out before condemning the PCM. A mechanic can use a scan tool to command the injector to fire while monitoring the voltage at the PCM pin to confirm this.
• Rodent Damage: Rodents can nest in the engine bay and chew on wiring, including the fuel injector harness. If you see signs of nesting material or chewed wires, this could be the cause.

Diagnosis Steps

1. Read the codes with an OBD-II scanner and confirm P0270 is present. 🎬 Watch: Understanding the P0270 code and what it means. Note any other codes, such as P0304.
2. Perform a detailed visual inspection of the fuel injector wiring harness for cylinder 4. Per TSB PIP4924D, check for chafing against the intake, valve covers, and fuel lines. On the 3.0L/3.6L V6, cylinder 4 is the middle cylinder on the bank closest to the radiator.
3. Disconnect the harness from the cylinder 4 injector. Check the connector for corrosion, bent pins, or damage.
4. Use a 'noid light' to test for a pulse signal at the injector connector while cranking the engine. A flashing light indicates the PCM is sending a signal. No light or a weak light points to a wiring or PCM issue.
5. If there is no pulse, check the wiring for continuity between the injector connector and the PCM using a multimeter. Repair any open or shorted wires found. A resistance over 1 ohm is suspect.
6. If the wiring and signal are good, check the resistance of the fuel injector itself. 🎬 Watch: A helpful guide on how to replace fuel injectors. With the injector disconnected, measure across its two terminals. A good injector will typically read between 10 and 18 ohms. A reading of 0 ohms indicates a short, and a very high or infinite reading indicates an open circuit.
7. As a final confirmation, swap the cylinder 4 injector with another one (e.g., cylinder 2). Clear the codes, run the engine, and see if the fault code 'moves' to the new cylinder (e.g., P0264). If it does, the injector is confirmed to be the problem.
8. If all wiring and the injector test good, the issue may be a rare fault within the PCM.

Parts You'll Likely Need

• Fuel Injector Wiring Connector Pigtail — This is the most common repair needed due to the wiring harness chafing issue described in TSB PIP4924D. Splicing in a new pigtail is often easier than repairing the wire close to the original connector.
  Trusted brands: ACDelco, Dorman (e.g., 645-207, though listed for other sensors, it is a common 2-pin connector style used for injectors)
  OEM price range: $25-$50
  Aftermarket price range: $15-$30
• Fuel Injector (OEM #12634126 (For 3.6L LFX V6, 2012-2014); 12638530 (For 3.0L/3.6L V6, 2010-2011)) — If the injector's internal coil has failed (shorted or open), it will cause a low circuit voltage reading and must be replaced.
  Trusted brands: ACDelco, Bosch, Standard Motor Products
  OEM price range: $100-$180
  Aftermarket price range: $50-$120

Related Codes That Often Appear With This One

• P0304 — This code means 'Cylinder 4 Misfire Detected'. Since P0270 indicates a problem with fuel delivery to cylinder 4, a misfire in that same cylinder is a very common and direct consequence.
• P0204 — This is a more generic 'Cylinder 4 Injector Circuit Malfunction' code. It can appear alongside P0270 as the PCM identifies the general circuit fault and the specific low-voltage condition.
• P0261, P0267, P0273, etc. — If multiple injector circuit low codes are present for cylinders on the same bank (e.g., P0264 for Cyl 2, P0270 for Cyl 4, P0276 for Cyl 6), it strongly suggests a wiring harness issue common to that bank of cylinders, or a problem with the shared power/ground circuit.

Technical Service Bulletins (TSBs) & Recalls

• PIP4924D: States that for a complaint of a misfire and injector codes (including P0270, P0204, etc.), the technician should carefully inspect the fuel injector wiring harness for rubbing or internal wire opens, particularly against the intake plenum, valve cover bolts, and fuel lines. This TSB applies to a wide range of 2009-2014 GM vehicles with 2.8L, 3.0L, and 3.6L engines.

Platform-Specific Known Issues

• A widespread issue documented in GM TSB #PIP4924D involves the fuel injector wiring harness rubbing through in various locations, causing a range of injector circuit codes, including P0270.
• On the 3.6L V6 engine, the front-facing cylinders (2, 4, 6) are easier to access than the rear bank (1, 3, 5) which is tucked under the intake manifold. Luckily, cylinder 4 is on the front bank.

Mechanic-Grade Diagnostic Values

• Fuel Injector Coil Resistance (2010-2011 3.0L LF1 & 3.6L LLT V6) — expected: 11 - 14 Ohms. Failure: A reading significantly outside this range, or showing an open (infinite) or shorted (near zero) circuit, indicates a failed injector.
• Fuel Injector Coil Resistance (2012-2014 3.6L LFX V6) — expected: 1.5 - 2.5 Ohms at 68°F (20°C). Failure: A reading outside this range indicates a failed injector. Note that resistance changes with temperature.
• Injector Circuit Wiring Resistance — expected: < 0.5 Ohms. Failure: Resistance greater than 0.5 Ohms between the PCM connector and the injector connector points to a fault in the wiring harness.
• Injector Pulse Width (at idle) — expected: 2 - 4 milliseconds (ms). Failure: A value of 0 ms for cylinder 4 while other cylinders are pulsing indicates the PCM is not commanding the injector, pointing to a PCM or wiring issue.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Injector Balance Test — This bidirectional test is used to functionally check an injector when wiring and resistance tests are inconclusive. The tool commands each injector to fire and measures the corresponding drop in fuel rail pressure. A minimal or excessive pressure drop for cylinder 4 compared to others indicates a faulty injector.
• GDS2 (GM Global Diagnostic System 2): Injector Test (Actuator Test) — This function allows a technician to command the injector to pulse on demand while the engine is off. It's used in conjunction with a noid light or multimeter to confirm if the PCM driver and wiring are capable of sending the signal to the injector connector.

OEM Part Supersession History

• 12638530 → 12669384 — Standard part revision and update by GM.
  Heads up: Part number 12638530 is for the 2010-2011 3.0L/3.6L LLT engines. Part number 12669384 is for the 2012+ 3.6L LFX engine. These injectors have different resistance values (LLT is high impedance, LFX is low impedance) and are not interchangeable. Using the wrong injector will cause performance issues and likely set new trouble codes.

Model Year Variations Within This Range

• 2009-2011: These models used the 3.0L LF1 or 3.6L LLT V6 engines. These are high-impedance fuel injection systems, and the injectors (PN 12638530) have a resistance of approximately 11-14 ohms. The ECM is typically a Bosch unit.
• 2012-2014: These models used the updated 3.6L LFX V6 engine. This is a low-impedance system, and the injectors (PN 12669384) have a much lower resistance of about 1.5-2.5 ohms. The ECM is a Delphi unit. The physical engine design also changed, with integrated exhaust manifolds. A specific GM bulletin (PI1067) also applies to 2013-2014 models, warning of a harness chafe point at the ECM bracket.
• 2009: The 2009 LaCrosse was the last year of the first generation, built on the GM W-body platform. While TSB PIP4924D includes this year, the physical routing of the injector harness and specific chafe points may differ from the second-generation (2010-2014) Epsilon II platform cars.