AutoCodes – Lexus – P0306 Lexus

P0306 Lexus Code - Cylinder 6 Misfire Detected

Quick Answer

When the engine misfires, high concentrations of Hydrocarbons (HC) enter the exhaust gas. Common causes include Intake air leak, Faulty spark plug #6, Faulty ignition coil #6. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P0306 Lexus indicates Cylinder 6 Misfire Detected.
Common causes: Common causes include Intake air leak, Faulty spark plug #6, Faulty ignition coil #6.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 32,052

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Aug 25, 2022

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
Comments
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Code P0306 Lexus Description

When the engine misfires, high concentrations of Hydrocarbons (HC) enter the exhaust gas. Extremely high hydrocarbon concentration levels can cause an increase in exhaust emission levels. Extremely high concentrations of hydrocarbons can also cause increases in the three-way catalytic converter temperature, which may cause damage to the three-way catalytic converter. To prevent this increase in emissions and to limit the possibility of thermal damage, the Engine Control Module (ECM) monitors the misfire count. When the temperature of the three-way catalytic converter reaches the point of thermal degradation, the ECM blinks the MIL. To monitor misfires, the ECM uses both the camshaft position sensor and the crankshaft position sensor. The camshaft position sensor is used to identify any misfiring cylinders and the crankshaft position sensor is used to measure variations in the crankshaft rotation speed. Misfires are counted when the crankshaft rotation speed variations exceed predetermined thresholds. If the misfire count exceeds the threshold levels and could cause emission control system performance deterioration, the ECM illuminates the MIL and stores a Diagnostic Trouble Code (DTC).

OBDII Code P0306 Lexus - Cylinder 6 Misfire Detected - AutoCodes.com — P0306 Lexus Code - Cylinder 6 Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0306 Lexus?

Intake air leak
Faulty spark plug #6
Faulty ignition coil #6
Clogged or faulty fuel injector #6
Fuel injectors #6 harness is open or shorted
Fuel Injectors #6 circuit poor electrical connection
Ignition coils #6 harness is open or shorted
Ignition coils #6 circuit poor electrical connection
Incorrect Fuel pressure
Faulty Mass Air Flow (MAF) Sensor
Faulty Engine Control Module (ECM)
Faulty Engine Coolant Temperature (ECT) Sensor

How to Fix the DTC P0306 Lexus?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

The P0306 code means that cylinder #6 is misfiring or is randomly misfiring. Start by checking for intake leaks and if no leaks are found the next step is to replace the spark plugs on cylinder #6. If the problem persists more tests need to be done to diagnose the problem. See "Possible Causes" for the most common problems.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0306 Lexus code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0306 Lexus Code

No Frequently Asked Questions about P0306 Lexus Code found.

Discuss the causes and fixes for P0306 Lexus OBDII Code

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Clifford Doyle
Date: July 18, 2019 at 7:04 pm

2003 LEXUS GS300, replaced plugs, plug wires, crank sensor, coils, igniter, throttle position sensor, cleaned throttle body, fresh gas, checked fuel injectors 13.3 to 13.5 all within range of one another. Hesitates to react when pressing accelerator, then kicks in to good RPM's.

Reply to Comment
OBDIITech
Date: July 20, 2019 at 5:31 am

Looks like you have done almost everything. I recommend also checking the air filter and the Mass Air Flow (MAF) sensor. Replace filter and clean the MAF. Have you check the fuel pressure?

Reply to Comment
Clifford Doyle
Date: December 9, 2019 at 12:27 am

I had checked the MAP. Pumped 8 gallons of old gas out through fuel pump under rear seat. Seem to pump out fairly fast. Observed when cutting and replacing coil connectors, very bad corrosion and cracked coating on wires.

Reply to Comment
Darren Frith
Date: June 28, 2025 at 4:28 pm

2010 lexus LS 460 L. Just replaced all 8 direct injectors, wiring harness, both fuel pump gaskets and the intake gasket. Went to overtake a slow car this morning, car fell flat on its face. CE light and traction control light come on. Shut car off, turned back on, CE light and TC light off, went home and got spare car. Hooked up reader after work and this code was stored.

Reply to Comment
- OBDIITech
  Date: June 30, 2025 at 10:36 am
  Thanks for the detailed info. Since you just replaced all 8 injectors, wiring harness, and intake gaskets, and now you're getting a P0306 (misfire on cylinder 6), there’s a good chance something got disturbed or didn’t seat right during reassembly.
  
  Here’s what I’d check first:
  1. Ignition coil on cylinder 6 – It may have gotten damaged or not plugged in fully during the injector job. Try swapping coil 6 with another cylinder and see if the misfire follows.
  2. Fuel injector connection – Even though the injectors are new, double-check that the connector on injector 6 is fully seated and the wiring isn’t pinched or pulled.
  3. Intake manifold gasket or vacuum leak near cyl 6 – A small air leak at the intake runner for that cylinder could cause a misfire under load.
  4. Carbon buildup on valves – These engines are direct injection, and carbon buildup can cause random misfires—especially under load. Might be worth considering a cleaning if it keeps happening.
  5. Traction control light – That usually comes on with a misfire because the ECU cuts power or torque to protect the drivetrain. Not a separate issue.
  If it only happened once under hard acceleration and hasn’t returned, it might’ve been a one-off misfire due to a connector or loose part. But I’d still start by swapping the coil and checking the injector harness on #6 closely. Let me know if you want help finding #6—it’s rear passenger side.
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