Lexus: What Does Error Code P0306 Mean?
The P0306 code means that a misfire has been detected in the number 6 cylinder. A misfire could be caused by worn, fouled, or damaged spark plugs, bad plug wires, or even a cracked distributor cap.
This article applies to the Lexus IS, RX, GS, LS, and ES (2005-Present)
Every Lexus vehicle comes equipped with an OBD connector which can be used to send messages to an OBD2 troubleshooting reader like the one below. Simply connect the scanning tool (or a computer with scanning software downloaded) to the connector (located under the steering wheel) and the readout will show you Diagnostic Trouble Codes that might be affecting your car. From there, you can look up the code at ClubLexus.com to learn what's going on and try to repair it yourself. If you are not comfortable diagnosing and repairing your car, please take it to a Lexus service center. Scanner programs and tools vary in price. An app can be purchased for $4.95, and an OBD -II Scanner/Code Reader can be purchased for anywhere between $19 and $300+ depending on what service functions you need.
P0306 Definition
The P0306 code means that the Misfire Monitor has detected more than a 2% variance in RPM between the firing of any two (or more) cylinders in the firing order. The term “misfire” refers to an incomplete combustion process inside the cylinder. When this becomes severe enough, the driver will feel a jerking action coming from the engine and/or powertrain.
P0306 Explained
An ignition system problem is one of the most common reasons for an engine to misfire. As the spark plugs, ignition cables, distributor cap and rotor, and ignition coil wear over time, their ability to transfer the needed spark to ignite the air/fuel mixture inside the combustion chambers becomes compromised. A misfire occurs insufficient amount of fuel is burning in a cylinder. The efficient burning of fuel is essential to engine operation as the combustion of fuel is what provides the energy to power the engine. A misfire from one or more cylinders can be caused by many reasons from a faulty ignition system, fuel system or internal engine failure
P0306 Symptoms
- Check Engine light is on
- Check engine light flashing
- Engine runs rough and shaking
- Lack of power from the engine
- Fuel smell from the exhaust
- Hesitations/jerking when accelerating
P0306 Common Causes
- Faulty or worn spark plugs *
- Distributor failure *
- Faulty fuel injector *
- Vacuum leak.
- Low fuel pressure.
- Camshaft sensor defective.
- Crankshaft sensor defective.
- Engine timing off
- Leaking head gasket
- Low engine compression
- Poor quality fuel
P0306 Diagnosis and Repair
Check for loose connectors at the ignition coils or for damaged wiring. Look for loose engine ground wires as well. These can cause random misfire conditions. Tighten or connect where necessary. Check the condition of your spark plugs and spark plug wires. If your vehicle is equipped with individual coil packs instead of spark plug wires, start by removing the cylinder 6 coil and swapping it with the cylinder number 4 coil. If the misfire moved to cylinder number 4, then you have determined that the coil pack is faulty and needs replacement. Replace spark plugs and spark plug wires/ignition coil packs if needed and recheck for misfires. Check fuel pressure. Low fuel pressure can cause intermittent misfires on multiple cylinders. When the pressure is below the specification, the engine does not receive the proper amount of fuel and will start to lean misfire. The fuel pump or fuel pressure regulator could be the source of the low fuel pressure. Check that the fuel injectors are functioning properly and activating. Random misfires can be a sign of faulty or clogged fuel injectors that need to be replaced. Also, check that the fuel injector wiring is not damaged and is connected properly.
- Broken valve spring
- Broken piston ring
- Worn valve guides
- Burned valve
- Timing chain or belt skipped tooth and engine is off time.
Final Notes
If you have any doubts about the cylinder being the source of the issue, then ask yourself if all of your basic maintenance has been done first? Items such as the fuel filter, air filter, spark plugs and spark plug wires are in good working order, as these are all possible candidates for a problem.
