P0303 on 2011-2015 Lexus RX HYBRID: Cylinder 3 Misfire Causes and Fixes

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

The 3.5L 2GR-FXE V6 engine in the RX 450h is generally very reliable. However, Lexus issued a Technical Service Bulletin (TSB) L-SB-0045-12 Rev for 2010-2017 models that specifically addresses misfire codes (P0300-P0306), often accompanied by rough running on a cold start. While ignition components are the most frequent culprits, this TSB points to faulty fuel injectors as a known issue 🎬 Watch: TSB repair procedure for Lexus RX450h misfire codes. requiring replacement. Accessing any component on cylinder 3 requires removing the upper intake manifold and cowl assembly, significantly increasing labor time compared to a misfire on the front bank.

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 or shaky idle, especially on cold start
• Hesitation or stumbling during acceleration
• Reduced engine power and poor throttle response
• Noticeable decrease in fuel economy
• Smell of unburnt fuel from the exhaust
• VSC (Vehicle Stability Control) light may also illuminate along with the Check Engine Light

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Ignition coils are a common failure point on most modern engines due to constant heat cycles and vibration. The coil for cylinder 3 is located in a high-heat area with less airflow, potentially leading to a shorter lifespan.
   How to confirm: The definitive test is to swap the ignition coil from cylinder 3 with an easily accessible cylinder on the front bank (e.g., cylinder 2, 4, or 6). This requires removing the intake manifold to access cylinder 3. After swapping, clear the codes and drive. If the code changes to P0302, P0304, or P0306, the coil is confirmed faulty.
   Typical fix: Replace the single faulty ignition coil. Given the significant labor to access the rear bank, it is highly recommended to replace all three rear ignition coils (cylinders 1, 3, 5) and all six spark plugs at the same time.
   Est. part cost: $35-$110 per coil
2. Worn Spark Plug 🔴 High Probability → Shop Spark Plug Lexus specifies long-life iridium spark plugs with a service interval of 120,000 miles. However, they can fail earlier. An overly wide gap from electrode wear or fouling from oil or carbon can prevent a strong spark and cause a misfire.
   How to confirm: After ruling out the ignition coil, inspect the spark plug from cylinder 3. Look for a worn or melted electrode, heavy carbon deposits, or oil fouling. A wet, fuel-soaked plug indicates it's not firing at all. Compare its condition to a plug from a working cylinder.
   Typical fix: Replace the spark plug in cylinder 3. Best practice, especially given the labor to access the rear bank, is to replace all six spark plugs (and often the rear three coils) at the same time if they are near or past their service life.
   Est. part cost: $15-$25 per plug
3. Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector A known issue highlighted by Lexus TSB L-SB-0045-12 Rev, which specifies replacing fuel injectors as a primary solution for cold-start misfires on this platform. Injectors can become clogged with fuel deposits or fail electronically.
   How to confirm: If swapping the coil and plug does not resolve the P0303 code, the fuel injector is the next likely cause. Diagnosis can involve using a scan tool to monitor misfire counts while wiggling the injector wiring, listening for the injector's 'click' with a stethoscope, or having a shop perform a fuel injector balance test. A professional scan tool like Toyota Techstream can perform a cylinder power balance test by individually disabling injectors to see the effect on engine RPM.
   Typical fix: Replace the fuel injector for cylinder 3. As with coils and plugs, replacing all three rear-bank injectors simultaneously is a common preventative strategy due to the labor involved in accessing them.
   Est. part cost: $80-$210

Rare But Worth Checking

• Low Engine Compression: This is a more serious mechanical issue, such as a burnt exhaust valve, worn piston rings, or a failed head gasket. A compression test followed by a cylinder leak-down test is required to diagnose this.
• Intake Manifold Gasket Leak: → Shop Engine Intake Manifold A vacuum leak from a failed intake manifold gasket near the runner for cylinder 3 can lean out the air/fuel mixture, causing a misfire. This would often be accompanied by a hissing sound and possibly lean condition codes (e.g., P0171, P0174).
• Wiring Harness Issue: Damage to the wiring or connector for the cylinder 3 ignition coil or fuel injector can cause an intermittent connection. This can be caused by rodent damage or chafing. A visual inspection and testing for continuity with a multimeter would be needed.
• Carbon Buildup on Intake Valves: While the 2GR-FXE in this vehicle uses port injection (which helps keep valves clean), related direct-injection Toyota engines (2GR-FSE) are known for carbon buildup issues. A ClubLexus user with a persistent P0303 on a port-injected ES350 (2GR-FE) found significant carbon on the cylinder 3 valves via a borescope after other parts were replaced.

Diagnosis Steps

1. Read the code from the OBD-II port using a scanner to confirm P0303 is the primary code. Note any other codes.
2. Review freeze frame data to see the engine speed, load, and temperature when the misfire occurred. This can provide clues (e.g., only happens when cold, as noted in TSB L-SB-0045-12 Rev).
3. Prepare for intake manifold removal. This is necessary to access cylinder 3. Gather a new intake manifold gasket set.
4. Once the manifold is off, swap the ignition coil from cylinder 3 with one from the front bank (e.g., cylinder 2).
5. Reassemble the intake manifold, clear the codes, and drive the vehicle. Re-scan for codes. If the code has moved to P0302, the ignition coil is the confirmed problem.
6. If the code remains P0303, the coil is not the issue. The next step is to replace the spark plugs. Given the labor, replace all six plugs, especially if they are over 100,000 miles old.
7. If the code still remains P0303 after a new coil and plugs, the problem is likely the fuel injector or a more complex issue.
8. The next logical step, with the intake already removed, would be to replace the cylinder 3 fuel injector, or all three rear injectors as a preventative measure, per TSB L-SB-0045-12 Rev.
9. If all ignition and fuel components have been addressed and the P0303 persists, perform an engine compression test on cylinder 3 to check for mechanical problems like a burnt valve or bad rings.
10. Inspect the wiring and connectors for both the ignition coil and fuel injector at cylinder 3 for any signs of damage, corrosion, or looseness.

Parts You'll Likely Need

• Ignition Coil (OEM #90919-A2007) — This is the most frequent cause of a single-cylinder misfire. They are electronic components that fail over time from heat and vibration.
  Trusted brands: Denso (OEM supplier), NGK, Standard Motor Products (SMP)
  OEM price range: $95-$135
  Aftermarket price range: $35-$85
• Spark Plug (OEM #90919-01247 (Denso FK20HR11)) — Spark plugs are a routine maintenance item. A worn or fouled plug cannot create a strong enough spark for proper combustion. Due to the labor, they should always be replaced when accessing the rear bank.
  Trusted brands: Denso (OEM), NGK
  OEM price range: $15-$22
  Aftermarket price range: $10-$18
• Fuel Injector (OEM #23209-31090) — Can become clogged or fail electronically, as noted in Lexus TSB L-SB-0045-12 Rev.
  Trusted brands: Lexus (OEM), Standard Motor Products (SMP)
  OEM price range: $130-$210
  Aftermarket price range: $80-$150

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or begins to affect other cylinders, a P0300 (Random/Multiple Cylinder Misfire Detected) may be stored alongside P0303.
• P0301, P0305 — These codes indicate misfires in the other rear-bank cylinders. If seen with P0303, it could point to a problem common to that bank, such as a vacuum leak from the intake manifold gasket on that side.
• P0171, P0174 — These codes indicate a "System Too Lean" condition on Bank 1 and Bank 2, respectively. A vacuum leak large enough to cause a misfire on cylinder 3 could also trigger one of these codes.

Technical Service Bulletins (TSBs) & Recalls

• L-SB-0045-12 Rev: Addresses MIL 'ON' with DTCs P0300-P0306 and/or rough running on initial start-up after a cold soak. The primary fix suggested is fuel injector replacement.
• L-SB-0044-19 Rev1: For later 2016-2019 models, this TSB addresses misfire DTCs and points to a fix involving ignition coil replacement and an ECM software update.

Platform-Specific Known Issues

• Lexus Technical Service Bulletin L-SB-0045-12 Rev was issued for 2010-2017 RX 450h models for misfire DTCs (P0300-P0306) and/or a rough run condition after a cold soak. The bulletin outlines a repair procedure that may involve replacing the fuel injectors.
• A separate TSB, L-SB-0044-19, for later model RX 450h (2016-2019) vehicles addresses similar misfire codes and may involve replacing an ignition coil and reprogramming the ECM, indicating ongoing ignition control logic updates for this engine family.

Mechanic-Grade Diagnostic Values

• Spark Plug Electrode Gap (New) — expected: 1.0 to 1.1 mm (0.039 to 0.043 in.). Failure: A gap wider than 1.4 mm (0.055 in.) on a used plug can cause weak spark and misfires.
• Ignition Coil IGT Signal (at ECM) — expected: Pulse generation should be visible on an oscilloscope during engine cranking or idling.. Failure: A missing or erratic pulse for cylinder 3 (IGT3) points to an ECM or wiring issue, not a bad coil.

Hidden / Shadow Codes Worth Checking

• Mode $06, TID $A2-$A7, CID $01-$0C: Toyota/Lexus vehicles heavily utilize Mode $06 data to store misfire counts for each cylinder during the current and last 10 driving cycles. Even before a P0303 code is set, a technician can view these counters on a capable scan tool to see if cylinder 3 is accumulating misfires. (see via Professional scan tool with Mode $06 functionality, such as Toyota Techstream.)

Scan Tool Commands That Help

• Toyota Techstream: Active Test: Control the Select Cylinder Fuel Cut — This is a power balance test used to confirm a weak cylinder. By commanding the fuel injector for cylinder 3 to turn off, a technician can observe the drop in engine RPM. If there is little or no RPM drop compared to other cylinders, it confirms cylinder 3 is not contributing power, pointing to a fuel, spark, or compression issue on that specific cylinder.
• Toyota Techstream: Active Test: Control the Injection Mode — For some 2GR engines, this test allows a technician to switch between different fuel injection modes to diagnose injector issues, though its primary use is not for single-cylinder misfires.

Wiring & Ground Locations

• C55 (Pin 38) — At the Engine Control Module (ECM).. This is the specific pin for the IGT3 signal, which is the trigger signal from the ECM to the ignition coil for cylinder #3. A technician can back-probe this pin to verify if the ECM is sending the command to fire.
• Engine Harness Grounds — The 2GR-FE engine harness typically has main grounding points on the valve covers, bolting to the chassis near the strut towers, and on the side of the cylinder head.. A poor or corroded engine ground can cause a weak spark across all cylinders or introduce electrical noise, leading to intermittent misfires that are difficult to diagnose. Ensuring these grounds are clean and tight is a critical step if ignition problems persist.

Real Owner Repair Stories

• ClubLexus Forum Member (Lexus ES350 with 2GR-FE (similar engine architecture)) — Persistent P0303 misfire code.
  ❌ Tried (didn't work) Swapping ignition coils, Replacing spark plugs
  ✅ What actually fixed it Using a borescope, the owner discovered significant carbon buildup on the intake valves of cylinder #3, while cylinder #5 was clean. The ultimate fix required mechanical cleaning of the carbon from the valves.

OEM Part Supersession History

• 90919-A2007 → 90919-A2013 — Part has been updated by the manufacturer. The new part is a direct replacement.
  Heads up: The original part number 90919-A2007 also replaces older numbers 90919-02251, 90919-A2002, and 90919-A2004.
• 23209-31090 → 23209-0P010 — Part has been updated by the manufacturer.

Model Year Variations Within This Range

• 2013-2015: Following a 2012 refresh for the 2013 model year, the RX series received additional body spot welds for increased rigidity and revised suspension tuning. While this doesn't directly affect the cause of P0303, it's a notable change within the specified vehicle range. The core engine (2GR-FXE) and its common failure points for this code remained the same.