P0305 on 2016-2019 Lexus RX HYBRID: Cylinder 5 Misfire Causes and Fixes

What's Unique About the 2016-2019 Lexus RX HYBRID

The 2016-2019 Lexus RX Hybrid uses the highly reliable 2GR-FXS V6 engine, which features both direct and port fuel injection (D-4S). While generally robust, this platform has specific Technical Service Bulletins (TSBs) related to misfire codes, including P0305. TSB L-SB-0044-19 and its revision explicitly state that for a MIL ON condition with P030x codes, the fix involves both diagnosing and replacing the faulty ignition coil and reprogramming the ECM with an updated calibration. This software update is crucial as it adjusts the misfire detection logic. 🎬 Watch: A detailed walkthrough of the TSB repair procedure. Another TSB, L-SB-0045-12 Rev, notes that some early models may experience a rough run on initial startup after a cold soak, which is a known symptom tied to these codes that may also be addressed by an ECM update.

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 (solid or flashing)
• Rough or shaky idle
• Engine hesitation or stumbling during acceleration
• Reduced engine power and poor fuel economy
• Noticeable engine vibrations
• Fuel odor from the exhaust
• Rough running on initial start-up after a cold soak, especially on 2016-2017 models

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Ignition coils are a primary failure point for single-cylinder misfires and are specifically called out in manufacturer TSB L-SB-0044-19 as the primary component to replace, in conjunction with an ECM update, to resolve P030x codes on this platform.
   How to confirm: Swap the ignition coil from cylinder 5 with another cylinder (e.g., cylinder 3, which is on the same rear bank). Clear the codes and drive the vehicle. If the code changes to P0303, the ignition coil is faulty. Cylinder 5 is on the rear bank, making access more difficult than the front bank.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace all three coils on the rear bank at the same time due to the labor required to access them. After replacement, the ECM should be checked for software updates per the TSB.
   Est. part cost: $75-$135 for one OEM (Denso) coil.
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Spark plugs have a finite service life (recommended replacement is every 60,000 miles). As a fundamental wear item, a worn or fouled plug is a very common cause for a misfire if it's past its service interval.
   How to confirm: After confirming the ignition coil is good, remove the spark plug from cylinder 5. Inspect it for wear (worn electrode), carbon fouling, or oil deposits. Compare it to a new plug. The gap should be between 0.024 to 0.071 inches, though specific OEM spec is preferred.
   Typical fix: Replace the spark plug in cylinder 5. It is best practice to replace all six spark plugs at the same time to ensure even performance, especially if they are near the end of their service life.
   Est. part cost: $15-$25 per OEM-brand (Denso/NGK) Iridium plug.
3. Clogged or Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector
   How to confirm: If ignition components are good, the fuel injector is the next likely cause. This can be confirmed by swapping the injector with another cylinder (a high-labor task) or by having a professional perform a fuel injector balance test. A leaking injector may also create a raw fuel smell.
   Typical fix: Replace the faulty fuel injector. This is a labor-intensive job, especially for cylinder 5 on the rear bank, as it requires removing the upper intake manifold. Costs can be high, with dealer estimates sometimes reaching several thousand dollars for injector replacement.
   Est. part cost: $150-$250 for one OEM injector.

Rare But Worth Checking

• Carbon Buildup on Intake Valves: The 2GR-FXS engine uses both direct and port injection (D-4S), which helps reduce carbon buildup compared to direct-injection-only engines. However, it can still occur over high mileage and lead to airflow issues for a specific cylinder, causing a misfire. This should be investigated if ignition and fuel system checks pass.
• Internal Engine Mechanical Issue: This could include low compression due to a worn valve, piston ring, or head gasket issue. This is uncommon on the well-regarded 2GR-FXS engine but should be investigated with a compression test if all other diagnostics fail.
• Vacuum Leak: A vacuum leak from a cracked hose or a leaking intake manifold gasket near the runner for cylinder 5 could lean out the air-fuel mixture, causing a misfire. This is less likely to affect only a single cylinder but is possible.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0305 and check for any other codes.
2. Identify cylinder 5. On the 2GR-FXS engine in a transverse layout, cylinder 5 is on the rear bank (closest to the firewall), in the middle. The rear bank cylinders are 1, 3, 5 (from passenger to driver side) and the front are 2, 4, 6.
3. Access the rear bank ignition coils. This requires removing the engine cover and potentially the upper intake manifold 🎬 Watch: How to access rear bank coils and plugs quickly. for full access.
4. Swap the ignition coil from cylinder 5 with the coil from cylinder 3 (same bank). Clear the codes, run the engine, and re-scan. If the code is now P0303, the coil is bad.
5. If the code remains P0305, swap the spark plug from cylinder 5 with cylinder 3. Clear codes, run the engine, and re-scan. If the code is now P0303, the spark plug is bad.
6. If the code remains P0305, inspect the wiring and connector for the cylinder 5 ignition coil and fuel injector for any visible damage, corrosion, or loose connections.
7. If no issues are found, the problem is likely a faulty fuel injector or a mechanical engine issue. Professional diagnosis, including a fuel injector balance test and a compression test, is recommended at this stage.
8. Crucially, check if the vehicle's ECM software has been updated per TSB L-SB-0044-19. A dealer can check the calibration ID. Even after replacing a part, this update may be required to fully resolve the misfire detection. Some owners report dealers may be hesitant to perform the update unless the specific code is present at the time of service.

Parts You'll Likely Need

• Ignition Coil (OEM #90919-A2013) — This is the most common failure part for a single-cylinder misfire and is the primary hardware fix cited in manufacturer TSB L-SB-0044-19 for this exact issue.
  Trusted brands: Denso, Delphi, NGK
  OEM price range: $95-$135
  Aftermarket price range: $45-$80
• Iridium Spark Plug (OEM #90919-01263) — Spark plugs are a routine maintenance item. If they haven't been replaced in over 60,000 miles, they are a likely cause. The OEM part number corresponds to Denso FK20HBR8.
  Trusted brands: Denso, NGK
  OEM price range: $18-$25
  Aftermarket price range: $14-$20
• Upper Intake Manifold Gasket Set — If accessing the rear bank components (coils, plugs, or injectors), the upper intake manifold must be removed. The gaskets are one-time use and must be replaced to prevent vacuum leaks.
  Trusted brands: Fel-Pro, Mahle, OEM
  OEM price range: $40-$60
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• P0300 — If the misfire condition is intermittent or becomes more widespread, a P0300 (Random/Multiple Cylinder Misfire Detected) may appear alongside P0305.
• P0301, P0303 — Misfires on other cylinders of the same bank (Bank 1, which includes cylinders 1, 3, and 5) could indicate a shared problem like a vacuum leak affecting that bank or a failing catalytic converter for that bank.
• P0171, P0174 — If a vacuum leak is the underlying cause of the misfire, a System Too Lean code for the corresponding bank (P0171 for Bank 1) may also be present.

Technical Service Bulletins (TSBs) & Recalls

• L-SB-0044-19 (and revision LSB004419): MIL ON With Misfire DTC(s) P0301, P0302, P0303, P0304, P0305, and/or P0306
• L-SB-0045-12 Rev: MIL ON with P030x codes and/or rough running on initial start-up after a cold soak

Platform-Specific Known Issues

• TSB L-SB-0044-19: Addresses a MIL ON condition with P030x codes for 2016-2019 RX450h models. The official repair procedure involves diagnosing the misfire, replacing the faulty ignition coil, and reprogramming the ECM with a new calibration to prevent recurrence.
• TSB L-SB-0045-12 Rev: Specifically notes that 2016-2017 RX 450h vehicles may exhibit a rough run on initial start-up after a cold soak in conjunction with P030x codes. This TSB also points towards an ECM software update as part of the solution.
• Rear Bank Access: Cylinder 5 is on the rear bank against the firewall. Replacing coils, plugs, or injectors for this cylinder is significantly more labor-intensive than for the front bank (cylinders 2, 4, 6) because the upper intake manifold must be removed.

Mechanic-Grade Diagnostic Values

• Low-Pressure Fuel System Pressure — expected: 196 to 833 kPa (28 to 121 psi). Failure: Pressure below this range could indicate a failing low-pressure fuel pump, which was subject to a recall on some models.
• High-Pressure Fuel System Pressure (at 3000 rpm) — expected: 2,400 to 19,500 kPa (348 to 2,828 psi). Failure: Readings outside this range can indicate a problem with the high-pressure fuel pump.
• Port Fuel Injector Resistance — expected: 11.6 to 12.4 Ω at 20°C (68°F). Failure: Resistance outside this range indicates a faulty injector coil winding.
• Techstream Misfire Monitor (Mode 6) — expected: The 'Rate' for cylinder 5 should be zero or very close to it on a healthy engine.. Failure: A high or consistently counting 'Rate' number for cylinder 5 confirms an active misfire, which is more reliable than the standard data list, especially under load.

Hidden / Shadow Codes Worth Checking

• Mode 6 Misfire Data (e.g., EWMA and Rate): Toyota/Lexus vehicles use a 'Monitor' screen in Techstream which shows misfire history (EWMA - Exponentially Weighted Moving Average) over the last 10 trips and the current misfire count ('Rate'). This is more detailed than a simple P-code and can show intermittent issues before a code is set. (see via Using Toyota's Techstream software, navigate to the 'Monitor' screen instead of the standard 'Data List' for the Engine ECU.)

Scan Tool Commands That Help

• Toyota Techstream: Active Test: Control the Select Cylinder Fuel Cut — This function allows a technician to individually disable a fuel injector. To test for a weak cylinder, you can cut fuel to cylinder 5. If there is little to no change in engine idle, it confirms cylinder 5 was not contributing properly. This helps isolate the issue to a specific cylinder after spark has been ruled out.
• Toyota Techstream: ECU Flash Reprogramming — This is required as part of the official fix for TSB L-SB-0044-19. After replacing a faulty ignition coil, the ECM must be reprogrammed with an updated calibration file to adjust misfire detection logic and prevent the code from returning. This requires a stable power supply of 13.5V during the procedure.
• Toyota Techstream: Active Test: Check the Cylinder Compression — This test cranks the engine with fuel and spark disabled to measure the relative speed of each cylinder. It can help identify a cylinder with low compression without using a manual gauge. Note: For 2015-2018 models with the 2GR-FKS engine, a known bug requires the engine to start cranking within 1 second of pressing the 'Start' button in the software for it to work correctly.

Wiring & Ground Locations

• Ignition Coil Connector — Directly on top of each ignition coil, one per cylinder.. The connector and its wiring are a potential point of failure. Check for corrosion, pushed-out pins, or damage to the harness, especially for cylinder 5 on the hard-to-access rear bank.
• Ground Points — Multiple ground points exist for the engine harness. A wiring diagram is needed for exact locations, but common spots are on the cylinder heads and engine block.. A poor ground for the ignition or injection system can cause erratic behavior, including misfires. While less likely to affect only one cylinder, it's a possibility if the ground is specific to a bank or component group. A wiring diagram manual is the best source for this.

Real Owner Repair Stories

• ClubLexus Forum (2007 ES350 (uses related 2GR-FE engine, similar diagnostics)) — Check engine light and VSC light on, code P0305.
  ❌ Tried (didn't work) A shop replaced all three rear ignition coils and all spark plugs.
  ✅ What actually fixed it The user took the car back to the shop for further diagnosis. The story highlights that even after replacing the most common parts (coils and plugs), the problem can persist, pointing towards less common causes like a fuel injector, wiring, or vacuum leak that require deeper investigation with live scan tool data.

OEM Part Supersession History

• 90919-02280, 90919-A2002, 90919-A2004, 90919-A2007 → 90919-A2013 — Standard part evolution for reliability and manufacturing improvements.
  Heads up: The latest part number, 90919-A2013, is the correct replacement for the specified vehicle range and replaces several older numbers. Using an older, superseded part is not recommended.

Model Year Variations Within This Range

• 2016-2019: There are no significant mechanical or electronic design changes within the 2016-2019 model year range for the 2GR-FXS engine and its control systems that would alter the diagnosis of a P0305 code. The refresh for this generation occurred in the 2020 model year.