Ignition Systems ControlOBD2 Codes

P0307 – Meaning, Causes, Symptoms, & Fixes

What Does Code P0307 Mean?

  • P0307 definition: Cylinder 7 misfire detected
  • Issue Severity: SEVERE – Stop driving immediately
  • Repair Urgency: Fix this code immediately (same-day if possible) to avoid ignition failure, catalytic converter damage, and dangerous conditions
  • Diagnosis: A multiple misfire can be caused by anything from faulty spark plugs to low engine compression. Because there are so many variables that could cause a misfire, the best cost savings is to take your car into a shop to have it diagnosed as quickly and accurately as possible.

Your vehicle moves when gasoline is burned and power is generated inside a chamber known as the cylinder. Most engines have a 4, 6, or 8-cylinder engine, where more cylinders typically mean more power. Power is generated by pistons that move up and down while fuel is ignited at very specific times. A misfire typically occurs when the timing of this ignition is off.  P0307 indicates that cylinder #7 is experiencing misfires. 

P0307 Causes

Misfires can be caused by many reasons from a faulty ignition system, fuel system, or internal engine failure. The most common reason for this to happen is faulty or worn-out spark plug coil packs, especially if it’s been a while since you had a tune-up.

  • Faulty or worn spark plugs and/or spark plug wires
  • Ignition issues, including failing or damaged ignition coils 
  • Distributor failure 
  • Faulty fuel injector
  • Vacuum leak
  • Low fuel pressure
  • Camshaft and/or crankshaft sensor defective
  • Engine timing off
  • Leaking head gasket
  • Low engine compression
  • Poor quality fuel that is old or contaminated

P0307 Symptoms

  • Check Engine Light is on or flashing
  • Engine runs rough, hesitates, or jerks when accelerating
  • Drivers may not notice any adverse conditions when driving
  • In some cases, drivers may experience decreased fuel economy, fuel smell from exhaust, rough idling, or lack of power from the engine
  • Commonly associated with error codes: P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0308

How Do I Fix Code P0307?

With a misfire fault, the first step is to get it diagnosed to figure out what is causing the engine to misfire. 

If your vehicle is misfiring and you’re not comfortable diagnosing this issue at home, we recommend finding a RepairPal certified shop nearby to pinpoint the problem and give an accurate estimate for repairs. 

These shops can not only help you figure out what’s going wrong before you waste time and money on the wrong parts, but they also offer a minimum 12-month, 12,000-mile warranty and stand behind all their estimates with guaranteed fair pricing.

How Much Does It Cost to Fix Code P0307?

P0307 can be caused by anything from old spark plugs to vacuum leaks to poor engine compression. It’s impossible to give an accurate estimate without properly diagnosing the issue first. 

If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time” (the time spent in labor diagnosing your specific issue). Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your P0307 code.

Possible Repair Costs for P0307

Once properly diagnosed, P0307 may require one or more of the following repairs to resolve the underlying issue. These prices are based on national averages and include parts and labor. Your cost may differ depending on your location and type of vehicle.

  • Spark plugs: $66-$250
  • Ignition Coils: $230-$640 (some cars require Intake manifold removal)
  • Spark plug wires: $180-$240
  • Fuel injectors: $1500-$1900
  • Vacuum leak: $100-$200
  • Fuel pump: $1300-$1700
  • Fuel pressure regulator: $200-$400

DIY Steps to Diagnose Code P0307

Engine code P0307 could be caused by a number of things, including faulty spark plugs, faulty ignition system, distributor failure, and more. If you’d like to try to fix code P0307 at home without throwing money at parts, you’ll want to follow the steps below for proper diagnosis. Keep in mind this is an intermediate-level diagnosis and repair and not recommended for beginners. Diagnosis requires more specialized equipment beyond what the FIXD Sensor can provide and it can be a time and labor-intensive process for inexperienced DIYers.

DIY difficulty level: Intermediate

This repair requires mechanical knowledge and is not recommended for beginners.

Tools/parts needed (our top picks from Amazon):

STEP 1: USE FIXD TO ENSURE NO OTHER ENGINE CODES ARE PRESENT.

Use FIXD to scan your vehicle to verify P0307 is the only code present. If other codes are present, they must be addressed first.

STEP 2: CHECK FOR LOOSE CONNECTORS OR DAMAGED WIRING AT THE IGNITION COILS. 

Look for loose engine ground wires as well. These can cause random misfire conditions. Tighten or connect where necessary.

STEP 3: CHECK THE CONDITION OF YOUR SPARK PLUGS AND SPARK PLUG WIRES.

Worn and old spark plug wires are common causes of random misfires. Replace spark plugs and wires if needed and recheck for misfires. 

> How to replace spark plugs in 4 easy steps

> How to identify a fouled spark plug

> How to test spark plug wires

> How to gap spark plugs

STEP 4: CHECK TO ENSURE YOUR ENGINE IS GETTING THE PROPER AMOUNT OF FUEL.

If you have determined that your ignition system is operating correctly, there may be a problem within your fuel system that is causing the random misfires. The following should be checked to ensure the engine is getting the proper amount of fuel.

  • 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.

> How to check fuel pressure

  • Check fuel injectors: Make sure 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.

> How to check fuel injectors by ear

> How to check fuel injectors with a digital multimeter

STEP 5: PERFORM ENGINE COMPRESSION AND LEAKDOWN TEST

If the ignition system and fuel system checks out, you may want to perform an engine compression test and leakdown test to see if there are any mechanical problems causing your misfire. 

Common mechanical problems that can cause misfires:

  • Leaking Head Gasket
  • Broken valve spring
  • Broken piston ring
  • Worn valve guides
  • Burned valve
  • Timing chain or belt skipped tooth and engine is off time.

Common P0307 diagnosis mistakes

Loose fitting electrical connectors and broken or disconnected vacuum hoses are often overlooked. Oxygen sensor(s) are another common misdiagnosis for P0307.

Still Need Help Fixing Code P0307?

If you’ve followed the steps above and are still experiencing misfires or check engine code P0307, please contact the FIXD Mechanic Hotline if you’re a FIXD Premium subscriber or find a RepairPal certified shop near you to get the right repairs at a fair price.

Justin-Hughes

Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

Justin Hughes
Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

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    6 Comments

    1. Hi my name is Steve I have a 98 Ford expedition 4×4 with a 5.4 code po307 came on and I fixed a vacuum leak then I had a heater line break and I fixed it ran fine then the code came on again so I replaced cylinder 7 spark plugs and coil ran fine so I replaced the other seven plugs and coils now the engine light came back on and the car is running really ruff and the same code came on again it does good but when you give it gas it runs like its out of balance …what could it be I have no clue what to do now or how to fix it thanks for your time

      1. Hey Steve my name is Jean I have a similar problem with my 98 5.4 l what was the outcome of your motor I fear I have an internal problem and I don’t want to waste time and money on plugs wires coil excetera please let me know your about your experience thank you

    2. How much can coast the repair for this issue ? ( cylinder 7 misfire )

      1. Mine for a 2011 chevy Silverado was 590$ because I had a full tuneup for 189, but then was told the valve cover needed to be replaced because of a gm design flaw oil was leaking in and it alwas caused problems in chlinder 7 or cylinder 1 and if it wasn’t replaced the problem would occur again and the tuneup cost would be wasted.

    3. I’ve replaced all 8 coil packs and all 8 plugs with motorcraft platinum plugs. It’s running about 95% better but still throws a po307 code when climbing a hill. My next move is replacing all 8 injectors.

    4. the missfire in my 2010 ram 1500 4×4 hemi was caused by an underlying issue. the dreaded “lifter tick.” The lifter and cam lobe on the lifter on cylinder 7 was damaged and caused the valve not to open properly thus not allowing the improper amount of fuel and air mix to enter the cylinder. After doing some research, I learned that on the newer hemi engines, the lifter tick is a common problem, but can be fixed with a little time and money. buyer beware! if you plan to purchase a 2010+ dodge crystler or plymouth with a hemi engine, beware of this issue.

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