P0301 on 2011-2015 Lexus RX HYBRID: Cylinder 1 Misfire Causes and Fixes

What's Unique About the 2011-2015 Lexus RX HYBRID

For the Lexus RX Hybrid with the 2GR-FXE engine, a known issue documented in Technical Service Bulletin (TSB) L-SB-0045-12 Rev is a potential rough run on initial start-up after a cold soak, which can trigger P0301 and other misfire codes. This suggests a specific sensitivity in the engine's management system under certain conditions. While the root causes are typical (plugs, coils), the symptom of a cold-soak misfire is a well-documented characteristic for this particular vehicle range. Some owners on ClubLexus have noted that this can also be related to fuel injectors, with one owner of a 2016 model mentioning a dealer covered the $2,111 replacement under warranty due to the TSB.

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 or flashing
• Rough idle, especially on a cold start
• Engine hesitation or stumbling during acceleration
• Noticeable lack of power
• Reduced fuel economy
• Smell of unburned fuel from the exhaust
• Shaking or vibration from the engine, especially at idle.

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Ignition coils are a common failure point on many modern engines as they age. The issue is also highlighted in Lexus TSBs for related models and is a frequent topic in owner forums.
   How to confirm: Swap the ignition coil from cylinder 1 with another cylinder (e.g., cylinder 3 on the same bank). Clear the codes and drive. If the code changes to P0303, the coil is faulty. This is the most recommended first diagnostic step.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace the corresponding spark plug at the same time. Many owners recommend using OEM or Denso-branded coils for reliability.
   Est. part cost: $55-$100
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Spark plugs are a regular maintenance item. The manufacturer recommends Iridium-tipped plugs, and using cheaper alternatives or extending the 120,000-mile service interval can lead to misfires. A visual inspection can reveal carbon fouling, oil contamination, or a worn electrode.
   How to confirm: Remove the spark plug from cylinder 1 and inspect it for wear, carbon buildup, oil fouling, or damage to the electrode or insulator. Compare it to a new plug to see the difference in wear.
   Typical fix: Replace the spark plug. It is best practice to replace all six spark plugs at the same time to ensure even performance and avoid future misfires on other cylinders.
   Est. part cost: $12-$25 per plug
3. Clogged or Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector The 2GR-FXE engine uses a combination of port and direct injection (on some versions). While robust, injectors can become clogged or fail. The cold-soak misfire TSB (L-SB-0045-12) points to fuel injectors as a potential solution in its repair procedure. ClubLexus forum discussions mention injector failure at relatively low mileage (e.g., 72k miles), with expensive dealer repair quotes.
   How to confirm: This is more complex to diagnose. A professional can perform a fuel injector balance test. A DIY method involves listening to the injector with a mechanic's stethoscope to ensure it's clicking. A multimeter can also be used to check the injector's resistance; the standard resistance for a 2GR-FE injector is 11.6 to 12.4 Ω at 20°C (68°F).
   Typical fix: Clean or replace the fuel injector for cylinder 1. Due to the labor involved in accessing the rear bank, some owners opt to replace all three injectors on that bank at once.
   Est. part cost: $100-$250

Rare But Worth Checking

• Intake Manifold Gasket Leak: → Shop Engine Intake Manifold A vacuum leak near the cylinder 1 intake runner can lean out the air/fuel mixture and cause a misfire specific to that cylinder. A smoke test is the most effective way to diagnose a vacuum leak.
• Low Engine Compression: This is a more serious mechanical issue, potentially caused by a bad valve, worn piston rings, or a faulty head gasket. A compression test followed by a leak-down test is needed to diagnose this.
• Carbon Buildup on Intake Valves: While the 2GR-FXE has port injection which helps clean the valves, carbon buildup can still occur over time, restricting airflow to a specific cylinder and causing a misfire. This is less common than on direct-injection-only engines but still possible.
• Faulty Engine Control Module (ECM): In very rare cases, the driver circuit within the ECM that controls the ignition coil or fuel injector for cylinder 1 can fail. Other TSBs for Lexus vehicles have involved ECM reprogramming to correct misfire detection logic, though this is more common on the 2016+ models.

Diagnosis Steps

1. Read the trouble code with an OBD-II scanner and confirm P0301 is present. Note any other codes and review freeze frame data to see the conditions (engine temp, RPM) when the misfire occurred.
2. Identify cylinder 1. On the transversely mounted 2GR-FXE V6 engine, the bank against the firewall (rear bank) is Bank 1. The cylinders are numbered 1, 3, 5, from the passenger side to the driver's side. Cylinder 1 is the rear cylinder closest to the passenger side of the vehicle.
3. Swap the ignition coil from cylinder 1 with the coil from cylinder 3 (the middle cylinder on the same rear bank). This is the most common and cost-effective first step.
4. Clear the codes, start the engine, and let it run or drive it briefly to replicate the conditions from the freeze frame data.
5. Re-scan for codes. If P0303 appears, the ignition coil you moved is bad and needs replacement.
6. If P0301 returns, the coil is likely good. Proceed to inspect the spark plug for cylinder 1. Look for wear, fouling, or damage. Replace if it appears worn or is past its service life.
7. If the coil and plug are good, the issue may be with the fuel injector, wiring, or a mechanical problem. At this point, more advanced diagnostics like checking injector resistance (expecting 11.6-12.4 Ω), performing a smoke test for vacuum leaks, or conducting an engine compression test are required.

Parts You'll Likely Need

• Ignition Coil (OEM #90919-A2007) — This is one of the most common failure points for a single-cylinder misfire. The OEM part number 90919-A2007 supersedes older numbers like 90919-A2002.
  Trusted brands: Denso (OEM supplier), NGK, Delphi
  OEM price range: $95-$125
  Aftermarket price range: $55-$85
• Iridium Spark Plug (OEM #90919-01247 (Denso FK20HR11)) — Spark plugs are a maintenance item and the direct source of ignition. A worn plug is a primary cause of misfires.
  Trusted brands: Denso (FK20HR11), NGK (ILFR6T11)
  OEM price range: $15-$20
  Aftermarket price range: $12-$18

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects multiple cylinders, a P0300 (Random/Multiple Cylinder Misfire) may be stored alongside P0301.
• P0302, P0303, P0304, P0305, P0306 — If other cylinders on the engine are also misfiring, their respective codes will be stored. The provided TSB L-SB-0045-12 Rev mentions these codes appearing together as part of the known cold-soak issue.
• C1201 — This code, related to Engine Control System Malfunction, often appears with engine trouble codes. In one instance on a Tacoma World forum for a 2GR-FE engine, a user reported C1201 alongside multiple P030x codes. The VSC (Vehicle Stability Control) light may also illuminate.

Technical Service Bulletins (TSBs) & Recalls

• L-SB-0045-12 Rev: Addresses rough running on initial start-up after a cold soak and the presence of misfire codes P0300-P0306 on 2010-2017 RX 450h vehicles. The procedure involves diagnostics that may lead to replacing fuel injectors.

Platform-Specific Known Issues

• A Lexus Technical Service Bulletin (L-SB-0045-12 Rev) for 2010-2017 RX 450h models notes that they may exhibit a MIL 'ON' with P030x codes and experience rough running on initial start-up after a cold soak. The repair procedure in the TSB involves diagnostics that can lead to fuel injector replacement.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 11.6 to 12.4 Ω at 20°C (68°F). Failure: A reading outside this range indicates a faulty injector.
• Fuel Pressure — expected: 304 to 343 kPa (44 to 50 psi). Failure: Pressure below this range could cause lean misfires, though it would typically affect multiple cylinders.
• Spark Plug Electrode Gap (New) — expected: 1.0 to 1.1 mm (0.039 to 0.043 in.). Failure: An incorrect gap can lead to weak or inconsistent spark.

Hidden / Shadow Codes Worth Checking

• Mode $06 Misfire Counts: The ECM tracks misfire counts for each cylinder, even before they are high enough to set a P030x code. This data can confirm which cylinder is misfiring intermittently. (see via A professional scan tool capable of reading Mode $06 data, such as Toyota's Techstream software.)

Scan Tool Commands That Help

• Toyota Techstream: Active Test: Control the Injection Volume for Each Cylinder — This bidirectional command allows a technician to individually disable fuel injectors one by one. If disabling the cylinder 1 injector causes no change in engine RPM, it confirms that cylinder was not contributing, pointing to a problem with its fuel, spark, or compression.
• Toyota Techstream: ECU Reprogramming (Flash Calibration) — For the subsequent generation (2016+), a TSB (L-SB-0044-19) explicitly requires reprogramming the ECM with an updated calibration file to fix misfire detection logic, along with replacing the coil. This highlights that software logic can be a factor.

Wiring & Ground Locations

• Engine Harness Grounds — The 2GR-FE engine family typically has critical ground points on the valve covers that connect to the chassis near the strut towers, and another ground on the side of the cylinder head.. A poor ground connection can cause erratic behavior in sensors and ignition components, leading to false sensor readings or weak spark, which can trigger misfire codes.
• ECM Location — On the RX 450h, the Engine Control Module (ECM) is typically located in the engine compartment on the right (passenger) side.. Knowing the ECM location is necessary for inspecting the harness connections for corrosion or damage if a wiring fault is suspected between the ECM and the cylinder 1 ignition coil or injector.
• Cylinder 1 Injector/Coil — Cylinder 1 is on the rear bank (against the firewall), closest to the passenger side of the vehicle. The fuel injectors are located on the intake manifold near the cylinder head.. Physical access to the cylinder 1 coil and injector is required for testing and replacement. The rear bank is significantly more difficult to access than the front.

OEM Part Supersession History

• 90919-A2002, 90919-A2004 → 90919-A2007 — Standard part revision and improvement by the manufacturer.
  Heads up: The newer part number 90919-A2007 is the correct replacement for the specified vehicle range and is backward compatible with the older numbers.
• 90919-02280 → 90919-A2013 — Part update for the next generation (2016+ RX450h) as noted in TSB L-SB-0044-19.
  Heads up: While physically similar, using parts specified for the AL20 generation (2016+) on an AL10 generation (2011-2015) vehicle is not recommended without confirming cross-compatibility, as internal electronics may differ.

Model Year Variations Within This Range

• 2010-2015: The 2GR-FXE engine in this generation primarily uses port fuel injection. The subsequent generation (2016+) introduced the 2GR-FXS, which added D-4S combined direct and port injection, making the fuel system and potential causes of misfires more complex.
• 2013-2015 (Facelift): The third-generation RX received a facelift for the 2013 model year, which included cosmetic updates and chassis stiffening. However, the core 2GR-FXE powertrain and common causes for P0301 remained the same through 2015.