P0302 on 2020-2021 Audi A6 Allroad: Cylinder 2 Misfire Causes and Fixes

What's Unique About the 2020-2021 Audi A6 ALLROAD

The 2020-2021 A6 Allroad uses the EA839 3.0L turbocharged V6 engine, which is shared across many modern Audi and Porsche models. While generally reliable, this direct-injection engine platform is known for ignition coils and spark plugs being common wear items that lead to misfires. While less common on these specific model years, earlier versions of this engine family (primarily 2017-2019) were susceptible to rocker arm failures that can also present as a misfire, making proper diagnosis important. Additionally, some owners have reported piston-related issues, though this is considered rare.

Diagnostic Flowchart

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

Symptoms You May Notice

• Rough or vibrating idle
• Hesitation or stumbling during acceleration
• Reduced engine power
• Flashing or solid Check Engine Light
• Decreased fuel economy
• Unusual fuel odor from the exhaust

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Ignition coils are a very common failure point on modern Audi engines due to high heat and electrical stress, and are considered a regular maintenance item. Oil leaks from valve cover gaskets can also contaminate the coil boots and cause failure.
   How to confirm: Swap the ignition coil from cylinder 2 (middle cylinder, passenger side) with another cylinder (e.g., cylinder 1). Clear the codes and run the engine. If the code changes to P0301, the coil is faulty.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace all six coils at the same time 🎬 Watch: A simple DIY guide for replacing coils and plugs, especially if they are original and the vehicle has over 60,000 miles, to ensure reliability and performance.
   Est. part cost: $40-$80 per coil
2. Worn or Fouled Spark Plug 🟡 Medium Probability → Shop Spark Plug Spark plugs are a standard wear item. Audi recommends replacement every 40,000 miles, but this can vary based on driving habits and engine tune.
   How to confirm: After ruling out the ignition coil, inspect the spark plug from cylinder 2. Look for wear on the electrode, carbon fouling, or oil deposits. You can also swap the plug with another cylinder to see if the misfire code follows.
   Typical fix: Replace the spark plug in cylinder 2. It is best practice to replace all six spark plugs as a set to ensure even performance. A special 12-point spark plug socket 🎬 See this walkthrough for changing spark plugs on an Audi V6 is required for this engine.
   Est. part cost: $25-$45 per plug
3. Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector As a direct-injection engine, the fuel injectors operate under very high pressure and can become clogged or fail electronically over time. While less common than ignition components, it's the next logical item to inspect.
   How to confirm: If swapping the coil and plug doesn't isolate the issue, the fuel injector is a likely suspect. This can be confirmed by swapping the injector with another cylinder, but this is a more labor-intensive job requiring fuel system depressurization and special tools. A professional may be needed.
   Typical fix: Replace the faulty fuel injector. It's mandatory to replace the Teflon seals and O-rings using special tools when an injector is replaced. Some sources suggest replacing all injectors on the same bank for balanced fueling.
   Est. part cost: $100-$250 per injector

Rare But Worth Checking

• Carbon Buildup on Intake Valves: Direct-injection engines like the EA839 spray fuel directly into the cylinder, so gasoline detergents don't clean the intake valves. Over time, carbon can build up, restrict airflow, and cause misfires, especially on cold starts. This usually requires professional cleaning (e.g., walnut blasting).
• Rocker Arm Failure: → Shop Engine Rocker Arm Early production EA839 engines (primarily 2017-2019 models) had a known issue with needle bearings in the rocker arms failing. This can cause a ticking noise and misfires, and if left unchecked, can lead to catastrophic engine damage. While less likely on 2020-2021 models due to revised parts, it's a severe mechanical issue to be aware of if basic fixes fail.
• Vacuum Leak: A leak in a vacuum hose, such as a cracked PCV hose or a faulty water pump leaking coolant into the vacuum system, can introduce unmetered air or fluid into the engine and cause a lean condition, leading to misfires. This would typically be accompanied by other codes (like a lean code P2177) or affect multiple cylinders.
• Piston or Compression Issues: In very rare cases, a misfire can be caused by a mechanical engine problem like a cracked piston, worn piston rings, or a damaged valve, leading to low compression in cylinder 2. Audi has extended the warranty on some EA839 engines for piston skirt issues. A compression test is required to diagnose this.

Diagnosis Steps

1. Read the fault codes with an OBD-II scanner to confirm P0302 and any other codes.
2. Identify Cylinder 2: On the 3.0L V6 (EA839), the cylinders are numbered 1-2-3 on the passenger side (Bank 1) and 4-5-6 on the driver's side (Bank 2), from front to back. Cylinder 2 is the middle cylinder on the passenger side.
3. Swap the Ignition Coil: Carefully disconnect and remove the ignition coil from cylinder 2. Swap it with the coil from cylinder 1 (front cylinder, passenger side).
4. Clear the codes and run the engine. If the code returns as P0301, the ignition coil is the problem. If it remains P0302, proceed to the next step.
5. Swap the Spark Plug: Move the coil back to its original position. Now, remove the spark plug from cylinder 2 and swap it with the one from cylinder 1. This requires a special 12-point thin-wall socket. Clear codes and run the engine.
6. If the code returns as P0301, the spark plug is faulty. If it remains P0302, the issue is not the plug or coil.
7. Inspect the Fuel Injector: At this point, the fuel injector is a likely suspect. This is a more advanced diagnostic step. You can check for a signal at the injector connector with a noid light or have a professional test the injector's flow.
8. Check for Mechanical Issues: If all else fails, a compression test and a cylinder leak-down test should be performed on cylinder 2 to check for internal engine problems like low compression, valve issues, or the rare rocker arm or piston failure.

Parts You'll Likely Need

• Ignition Coil (OEM #06E905115G) — This is the most common failure item causing a single-cylinder misfire on this engine. The part number has been superseded multiple times; 06E905115G is a recent, common revision.
  Trusted brands: Bosch, NGK, Eldor, APR
  OEM price range: $60-$90
  Aftermarket price range: $40-$70
• Spark Plug (OEM #06M905606F) — A standard maintenance item that can cause misfires when worn or fouled. Requires a special 12-point socket for removal/installation.
  Trusted brands: NGK (OEM supplier, model SILKGR9A7ES), Bosch, Denso
  OEM price range: $30-$45
  Aftermarket price range: $25-$35

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affecting other cylinders, a P0300 (Random/Multiple Cylinder Misfire) may be stored alongside P0302.
• P0301, P0303, P0304, P0305, P0306 — If other cylinders are also misfiring due to a systemic issue like bad fuel, failing coils, or carbon buildup, their specific codes may appear as well.
• P2177 — A 'System Too Lean Off Idle' code can sometimes appear with misfire codes if a vacuum leak is the root cause, allowing unmetered air into the engine.

Technical Service Bulletins (TSBs) & Recalls

• A0123802069038_4: Provides information for when the MIL is on and cylinder misfires are detected (DTCs P0300-P0306) on 2021 models.
• A0124212069038_5: Provides information for when the MIL is on and cylinder misfires are detected (P0300-P0306) on 2020 models.
• A0123912069038_5: Provides information for when the MIL is on with DTCs P0300-P0306 on 2020 models.

Platform-Specific Known Issues

• Audi has issued Technical Service Bulletins (TSBs) related to misfire detection on this platform, sometimes requiring a software update at the dealership if ignition components are confirmed to be good.
• Early production EA839 engines (2017-2019) had a higher incidence of rocker arm bearing failure, which can cause misfires. While less common on 2020-2021 models due to revised parts, it is a known severe failure mode for this engine family that can present with a ticking noise.
• A known water pump failure on the EA839 can leak coolant into the engine's vacuum system, potentially causing lean conditions and misfires across multiple cylinders.

Mechanic-Grade Diagnostic Values

• Low-Pressure Fuel Pump (LPFP) pressure — expected: 4 to 6 bar. Failure: Pressure below this range can starve the high-pressure pump, leading to misfires under load.
• High-Pressure Fuel Pump (HPFP) rail pressure — expected: Up to 200 bar, depending on engine load.. Failure: A failure to reach or maintain target pressure under load, visible on a scan tool, indicates a failing HPFP.

Hidden / Shadow Codes Worth Checking

• Live Misfire Counters: The ECU maintains a running count of misfires for each cylinder, which can be viewed before they are frequent enough to trigger a persistent P030x code. This allows for early diagnosis of a developing issue. (see via Using a VAG-specific scan tool like VCDS or ODIS. In Advanced Measuring Values, search for terms like 'misfire' to find 'Misfire recognition – cylinder X' and 'Total misfire count'.)

Scan Tool Commands That Help

• VCDS (VAG-COM) or ODIS: Advanced Measuring Values - Misfire Counters — This should be used to diagnose an intermittent or developing misfire. Watching the live counts for each cylinder while driving or performing throttle snaps can help identify which cylinder is problematic, even if a permanent code has not yet been set.

Wiring & Ground Locations

• Main Engine Ground — In the right (passenger side) of the engine compartment, on the frame rail near the alternator.. A corroded or loose main engine ground can cause a host of electrical issues, including weak spark, which can lead to misfires. This is a critical check for any electrical or ignition-related fault code.

Real Owner Repair Stories

• 034Motorsport Technical Discussion (Audi S4 (B9) with EA839 engine) — A persistent, recurring misfire on a single cylinder (cylinder 2 in this example).
  ❌ Tried (didn't work) Replacing the fuel injector on the affected cylinder multiple times.
  ✅ What actually fixed it The Engine Control Unit (ECU) was faulty. The driver circuit for that specific injector was failing, causing the new injectors to fail prematurely. Replacing the ECU resolved the problem permanently.
• Reddit user dsocohen (2019 Audi SQ5 with EA839 engine) — Misfiring for weeks.
  ❌ Tried (didn't work) Multiple unspecified attempts to address the misfire.
  ✅ What actually fixed it Diagnosis concluded the likely cause was a mechanical rocker arm fault. The only way to confirm was to remove the cylinder head for inspection, indicating the problem was not a simple ignition or fuel component.

"I Checked Everything" — The Actual Cause

• A known failure on the EA839 is the water pump, which is vacuum-actuated. The pump can fail internally and leak coolant directly into the engine's vacuum lines. This will not be detected by a traditional intake smoke test, as the system is sealed from the outside. The coolant in the vacuum system can cause lean conditions, stumbling, and misfires that may appear random or affect multiple cylinders, baffling technicians who find no external vacuum leaks.

OEM Part Supersession History

• 06E-905-115-A through 06E-905-115-F → 06E-905-115-G — Standard revision and improvement process by the manufacturer to increase reliability and performance.
  Heads up: The newer 'G' revision is backward-compatible and is the recommended replacement for all prior versions.

Model Year Variations Within This Range

• 2020-2021: There are no significant mechanical differences in the EA839 engine or its related components between the 2020 and 2021 model years that would affect the cause or diagnosis of a P0302 code. Changes were limited to feature packaging and cosmetic options.