P0306 on 2013-2020 Audi A7: Cylinder 6 Misfire Causes and Fixes

What's Unique About the 2013-2020 Audi A7

The Audi A7 platform, across both the C7 (supercharged) and C8 (turbocharged) generations, uses sophisticated 3.0L V6 direct-injection engines. While powerful, these engines are known for having ignition coils as a common wear item. For correct diagnosis, it's crucial to know the cylinder layout: Bank 1 (passenger side) contains cylinders 1, 2, and 3 (front to back), while Bank 2 (driver's side) contains cylinders 4, 5, and 6 (front to back). Therefore, P0306 points to the rearmost cylinder on the driver's side. Additionally, as direct-injection engines, they are inherently prone to carbon buildup on the intake valves over time, which can restrict airflow and cause misfires that are not related to the ignition or fuel system.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: This year range covers two Audi A7 generations: the C7 (2013-2018) with a 3.0L supercharged V6 (EA837, e.g., CREC) and the C8 (2019-2020) with a 3.0L turbocharged V6 (EA839). While the fundamental causes of a P0306 misfire are the same, specific part numbers for ignition coils and spark plugs will differ between these engines. The supercharged engine is also known for a leaking intercooler (located within the supercharger) which can drip coolant into cylinders 3 and 6, causing misfires.

Symptoms You May Notice

• Flashing or solid Check Engine Light
• Rough or vibrating idle.
• Engine hesitation or stumbling during acceleration.
• Noticeable loss of engine power.
• Reduced fuel economy.
• Smell of unburnt gasoline from the exhaust
• Popping or backfiring sounds from the exhaust.

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability Ignition coils are a well-documented common failure item on modern Audi engines, typically requiring replacement every 60,000-80,000 miles.
   How to confirm: Swap the ignition coil from cylinder 6 with another cylinder (e.g., cylinder 5). Clear the codes and drive. If the code changes to P0305, the coil is bad.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace all six coils at the same time for preventative maintenance, especially on higher-mileage vehicles.
   Est. part cost: $50-$112 per coil.
2. Worn or Fouled Spark Plug 🔴 High Probability Spark plugs are a regular maintenance item with a typical service interval of 40,000-55,000 miles on the 3.0T engine. If they are past their service interval, they are a likely cause of a misfire.
   How to confirm: After ruling out the coil, remove the spark plug from cylinder 6. Inspect it for a worn electrode, carbon fouling, oil contamination, or a cracked insulator. Ash fouling on the plug for cylinder 3 or 6 can be a sign of a leaking supercharger intercooler on C7 models.
   Typical fix: Replace the spark plug. It is best practice to replace all six spark plugs at the same time 🎬 See this easy DIY walkthrough for replacing coils and plugs. to ensure even performance.
   Est. part cost: $20-$50 per plug.
3. Clogged or Faulty Fuel Injector 🟡 Medium Probability Direct fuel injectors operate under high pressure and can become clogged with carbon or fail electronically over time, leading to improper fueling.
   How to confirm: This is more difficult to diagnose. A professional can perform a fuel injector balance test. A DIY method is to swap the fuel injector from cylinder 6 with another cylinder, but this is a more involved job requiring new seals and potentially special tools.
   Typical fix: Replace the faulty fuel injector. This is a more involved job than a coil or plug and requires replacing the Teflon seals.
   Est. part cost: $150-$300 per injector.
4. Intake Valve Carbon Buildup 🟡 Medium Probability As direct-injection (TFSI) engines, fuel is sprayed directly into the cylinder, so it does not wash over and clean the intake valves. Oil vapor from the PCV system bakes onto the hot valves, forming carbon deposits that restrict airflow, a condition that typically becomes problematic after 60,000 miles.
   How to confirm: Visually inspect the intake valves using a borescope inserted into the intake ports. This is the only definitive way to confirm.
   Typical fix: The intake manifold (and supercharger on C7 models) must be removed and the valves cleaned, typically through a process called walnut shell blasting. 🎬 Watch: How to scrape and walnut blast your intake valves. This is a labor-intensive job.
   Est. part cost: $0 (cleaning service cost is labor)

Rare But Worth Checking

• Low Engine Compression: Although rare, a mechanical issue like a worn piston ring, a failing valve, or a head gasket leak can cause a persistent misfire. On early C8 models (2018-2019), a known issue with rocker arm failure can cause valvetrain damage, leading to misfires and a distinct ticking noise. A compression test is needed to diagnose this.
• Vacuum Leak: A leak in a vacuum hose or intake manifold gasket can introduce unmetered air, leaning out the mixture and causing a misfire. A common failure point is the PCV (Positive Crankcase Ventilation) valve, which can rupture, causing a high-pitched whistle, unstable idle, and vacuum-related codes.
• Leaking Supercharger Intercooler (C7): On the supercharged EA837 engine, the two intercooler cores housed inside the supercharger can leak coolant. Due to their location, this coolant often drips directly into cylinders 3 and 6, causing misfires that seem to have no ignition or fuel-related cause.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0306 and check for any other stored codes. An advanced scanner (like VCDS) can be used to monitor the misfire counter for cylinder 6 in real-time.
🎬 Watch: How to diagnose a misfire on your 3.0T engine.
2. Locate cylinder 6. On the 3.0L V6, it is the rearmost cylinder on the driver's side (Bank 2).
3. To quickly test the ignition coil, swap the coil from cylinder 6 with the coil from an adjacent cylinder (e.g., cylinder 5).
4. Clear the codes and test drive the vehicle. If the code returns as P0305, you have confirmed the ignition coil is the faulty part.
5. If the code remains P0306, perform the same swap test with the spark plugs.
6. If the coil and plug are good, inspect the wiring harness and connector going to the cylinder 6 coil and fuel injector for any damage or corrosion.
7. If all ignition components are verified to be working, the next likely causes are a faulty fuel injector, significant carbon buildup, or a leaking supercharger intercooler (on C7 models).
8. A professional diagnosis may be needed at this stage, which would involve a fuel injector flow test, a compression test, and a borescope inspection of the intake valves.

Parts You'll Likely Need

• Ignition Coil (OEM #C7 (Supercharged): 06E905115G / C8 (Turbocharged): 06E905110K (Verify by VIN)) — This is the most frequent failure point for a P0306 code on this vehicle.
  Trusted brands: Bosch, Eldor, NGK, APR
  OEM price range: $80-$120
  Aftermarket price range: $50-$90
• Spark Plug (OEM #C7 (Supercharged): 101905611G (NGK PFR8S8EG) / C8 (Turbocharged): 06M905606G (Verify by VIN)) — As a standard maintenance item, a worn spark plug is the second most common cause of a single-cylinder misfire.
  Trusted brands: NGK, Bosch, Denso
  OEM price range: $30-$50
  Aftermarket price range: $20-$35

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects multiple cylinders, the ECM may log a P0300 (Random/Multiple Cylinder Misfire) code in addition to P0306.
• P0301, P0302, P0303, P0304, P0305 — The presence of other cylinder-specific misfire codes indicates a problem affecting the entire engine or one bank, such as a major vacuum leak, fuel delivery issue, or carbon buildup across all cylinders. Several TSBs list these codes together.
• P130A — A manufacturer-specific TSB for 2013 models notes that P0306 can be stored along with P130A, which relates to the ECM hiding or disabling a cylinder to prevent damage when a severe misfire is detected. This is often triggered by carbon buildup under heavy load.

Technical Service Bulletins (TSBs) & Recalls

• A0124212069038_5: Notes P0306 for MIL illumination and cylinder misfires on 2020 models.
• A0123802069038_4: Mentions P0306 for MIL on and misfires on 2019 models, and points to a software update as the solution.
• 01138920337681 (Superseded by A01132720337682): States that P0306 can be stored with DTC P130A in the ECM on 2013 models and requests data collection.
• A0123912069038_5: A bulletin for 2020 models regarding MIL illumination with DTCs including P0306.
• A0123612069038_3: A bulletin for 2019 models regarding the MIL being on with DTCs including P0306.

Platform-Specific Known Issues

• Audi has released multiple Technical Service Bulletins (TSBs) that include code P0306 for illuminated check engine lights and misfires. Some of these bulletins recommend a software update for the ECM as a first step to correct misfire detection sensitivity.
• A TSB for 2013 models specifically mentions that a cylinder misfire fault (P0301-P0306) can be stored in conjunction with code P130A in the ECM, often related to carbon buildup.
• The direct-injection design of the 3.0L TFSI engines makes them highly susceptible to performance-robbing carbon deposits on the intake valves, which can cause misfires.
• On C7 models with the supercharged engine, the internal intercoolers can leak coolant directly into cylinders 3 and 6, causing a persistent misfire that is often misdiagnosed as an ignition or fuel issue.

Mechanic-Grade Diagnostic Values

• Low-Pressure Fuel System — expected: 3.0 to 6.0 bar (43 to 87 PSI) before the high-pressure pump.. Failure: Pressure below specification can starve the High Pressure Fuel Pump (HPFP), leading to misfires under load.
• High-Pressure Fuel System — expected: 30 to 125 bar (435 to 1812 PSI) at the fuel rail, depending on load.. Failure: Pressure that does not respond to engine load or is significantly below the specified value requested by the ECM indicates a failing HPFP or a leak.
• Long-Term Fuel Trim (VCDS Measuring Block 032) — expected: Typically within +/- 10%. Values near 0% are ideal.. Failure: A high positive percentage (e.g., >10%) indicates the engine is compensating for a lean condition (like a vacuum leak). A high negative percentage indicates a rich condition (like a leaking injector).
• Ignition Coil Connector Voltage (Pin 2) — expected: Battery voltage (approx. 12V) with key on, engine off.. Failure: No voltage indicates a problem with the power supply (fuse/relay) to the coil.
• Ignition Coil Connector Ground (Pin 3) — expected: Continuity to ground.. Failure: No continuity (high resistance) indicates a broken ground wire in the harness, which will prevent the coil from firing.

Scan Tool Commands That Help

• VCDS (VAG-COM): Measuring Blocks 014, 015, 016 (CAN) or Advanced Measuring Values (UDS) — Use this to monitor live misfire counts for each individual cylinder. This is the most effective way to confirm an active misfire on cylinder 6 and to see if the misfire moves to another cylinder after swapping components like ignition coils or spark plugs.
• VCDS (VAG-COM): Measuring Block 032 (Fuel Trims) — Use this to check long-term fuel adaptations at idle (additive) and under load (multiplicative). A high positive value in the additive field strongly suggests an unmetered air/vacuum leak, which can cause misfires.
• VCDS (VAG-COM): Measuring Block 106 or 140 (Fuel Rail Pressure) — Use this to monitor actual vs. specified fuel rail pressure. If the actual pressure cannot keep up with the specified pressure, especially under load, it points to a fuel delivery problem (low-pressure pump, high-pressure pump, or clogged filter).

Wiring & Ground Locations

• Cylinder 6 Ignition Coil Connector (T4fm) — On the rearmost ignition coil on the driver's side of the engine.. This connector provides power, ground, and the trigger signal from the ECM. A wiring diagram shows Pin 2 is power (from fuse), Pin 3 is ground, and Pin 1 is the signal wire. Verifying power and ground here is a key step if a new coil doesn't fix the misfire.
• Ground Connection (13) — In the engine compartment on the right side, on the frame rail near the alternator.. This is a primary engine ground point. A loose or corroded connection here can cause intermittent and hard-to-diagnose electrical issues, including weak spark or erratic ignition coil behavior across the engine.
• Earth Connection (484) — Located within the engine pre-wiring harness.. A wiring diagram specifically identifies this as the ground connection for ignition coils 4, 5, and 6 (Bank 2). A fault in this internal harness ground would affect the entire driver's side bank, likely causing multiple misfire codes (P0304, P0305, P0306).

Real Owner Repair Stories

• AudiWorld Forums user 'lichunz' (B8 Audi S4 (shares 3.0T supercharged engine with C7 A7)) — Misfires on cylinders 5 and 6 (P0305, P0306) along with cylinder disabling code (P130A).
  ❌ Tried (didn't work) Replaced spark plugs, Swapped ignition coils between cylinders
  ✅ What actually fixed it The final cause was a cracked intercooler inside the supercharger that was leaking coolant into cylinder 6.
• AudiWorld Forums user (2014 Audi A7 3.0 TFSI with 75,000 miles) — Rough idle or a 'shiver' when idling.
  ❌ Tried (didn't work) Using fuel injector cleaner
  ✅ What actually fixed it Another user reported resolving a similar smooth-running issue on their 2012 A7 by using CRC Intake Valve and Turbo Cleaner spray and switching to a higher quality engine oil (Liqui Moly), suggesting a mild case of carbon buildup was the cause.
• Ross-Tech Forums user 'Itsmys4' (2018 Audi S4 (shares 3.0T turbocharged EA839 engine with C8 A7) with 48k miles) — Ticking noise from under valve covers, misfires.
  ❌ Tried (didn't work) Dealer diagnosis suggested it was a normal fuel injector tick.
  ✅ What actually fixed it The owner self-diagnosed and replaced failed rocker arms, which is a known issue on this engine. The repair was a 'massive success' and resolved the running issues.

"I Checked Everything" — The Actual Cause

• In many cases on the 3.0T TFSI engines, a persistent misfire that returns after replacing ignition coils and spark plugs is caused by carbon buildup on the intake valves. This condition restricts airflow into the cylinder but will not be detected by a smoke test, which is designed to find vacuum leaks in the intake path. A borescope inspection of the valves is the correct next step when ignition components check out and a smoke test is clean.

OEM Part Supersession History

• 06E905115A, B, C, D, E, F → 06E905115G — Internal revisions to improve reliability and prevent premature failure.
  Heads up: These are for the C7 (supercharged) EA837 engine. While older revisions work, it is always recommended to use the latest available part number (G or later) when replacing.
• 06H905110G, H, L → 06H905110P — Internal revisions for improved durability and energy output.
  Heads up: These are for the C8 (turbocharged) EA839 engine. Do not use coils intended for the C7 supercharged engine.

Model Year Variations Within This Range

• 2013-2018 (C7, Supercharged): These models use the EA837 engine and are uniquely susceptible to misfires in cylinders 3 and 6 caused by internal coolant leaks from the intercooler cores housed within the supercharger assembly.
• 2019-2020 (C8, Turbocharged): These models use the EA839 engine. Early versions of this engine have a known potential for rocker arm bearing failure, which can lead to valvetrain damage and misfires. This is not an issue on the earlier supercharged engines.
• 2016+ (C7.5, CREC engine): The refreshed C7.5 generation introduced the CREC version of the 3.0T engine, which added multi-port fuel injection (MPI) alongside the direct injection (GDI). This dual-injection system sprays fuel onto the intake valves, significantly reducing the carbon buildup issues that plagued earlier GDI-only versions and made them prone to misfires.