P0306 on 2013 Audi Q5 3.0T: Cylinder 6 Misfire Causes and Fixes

What's Unique About the 2013-2013 Audi Q5

The 3.0T supercharged engine in the Q5 is a direct-injection (TFSI) engine. This design, while efficient, is known for three specific issues that commonly lead to misfires. First, without fuel washing over the intake valves, oil vapors from the crankcase ventilation (PCV) system can bake onto the hot valves, causing significant carbon buildup that restricts airflow, especially to cylinders 5 and 6. Second, the PCV system itself is a known failure point, and a bad PCV valve can create vacuum leaks or other issues that trigger misfires. Third, the supercharger houses two internal intercoolers (charge air coolers) that can develop coolant leaks, dripping coolant directly into the intake ports for cylinders 3 and 6, causing persistent misfires.

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
• Noticeable loss of engine power
• Flashing Check Engine Light
• Reduced fuel economy
• Engine may go into a protective "limp mode"
• Sweet smell of coolant from the exhaust (if caused by intercooler leak)
• High-pitched whistling or sucking noise from the engine bay at idle (if caused by PCV failure)

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Ignition coils are a very common failure item on modern Audi engines due to high heat and electrical stress. Many owners consider them a wear item.
   How to confirm: Swap the ignition coil from cylinder 6 with another cylinder (e.g., cylinder 5, the middle one on the driver's side). Clear the codes and drive. If the code changes to P0305, the coil is bad.
   Typical fix: Replace the faulty ignition coil. Many owners replace all six at once as a preventative measure if they are original and have high mileage, often using the red 'R8' style coils as a common upgrade.
   Est. part cost: $35-$75
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Spark plugs are a regular maintenance item with a service interval of 40,000-55,000 miles. Issues like oil consumption, a leaking intercooler dripping coolant, or excessive carbon can foul them prematurely.
   How to confirm: After ruling out the coil, remove the spark plug from cylinder 6. Inspect it for a worn electrode, heavy carbon deposits, or oil/coolant residue (a white/pink crust suggests a coolant leak). Compare it to a plug from a healthy cylinder.
   Typical fix: Replace the spark plug in cylinder 6. It is best practice to replace all six spark plugs as a set to ensure consistent performance.
   Est. part cost: $15-$25 per plug
3. Leaking Supercharger Intercooler 🟡 Medium Probability → Shop Turbocharger The 3.0T supercharger has two integrated liquid-to-air intercoolers that are a known failure point. They can develop internal leaks, dripping coolant into the intake ports. Due to the manifold design, this often affects cylinders 3 and 6 most directly.
   How to confirm: The primary symptom is mysterious coolant loss with no visible external leaks. A borescope inspection of the intake port with the supercharger removed will show evidence of coolant. In some cases, a pressure test of the intercooler's dedicated cooling circuit can confirm a leak.
   Typical fix: The supercharger must be removed to replace the faulty intercooler core(s). It is highly recommended to replace the PCV valve, thermostat, and both intercooler cores at the same time due to the significant labor overlap.
   Est. part cost: $180-$500 per intercooler core
4. Carbon Buildup on Intake Valves 🟡 Medium Probability As a direct-injection engine, fuel doesn't clean the intake valves. Oil vapor from the PCV system bakes onto the valves, restricting airflow and causing misfires, especially under heavy load. This is a well-documented issue on the 3.0T engine, often becoming problematic after 60,000-80,000 miles.
   How to confirm: This requires a visual inspection using a borescope inserted into the intake ports. Misfires that only occur at high RPM or under heavy load often point to this cause. Forum discussions note this can particularly affect cylinders 5 and 6.
   Typical fix: The intake manifold and supercharger must be removed, and the valves must be manually cleaned, typically through walnut blasting or with specialized 🎬 Watch how to properly scrape and walnut blast your valves. solvents and brushes.
   Est. part cost: $20-$50 for gaskets
5. Failed PCV Valve / Oil Separator 🟡 Medium Probability → Shop PCV Valve The PCV valve diaphragm is known to tear on the 3.0T engine, creating a significant unmetered vacuum leak that disrupts the air-fuel mixture and can cause misfires across one or multiple cylinders.
   How to confirm: A classic sign is a high-pitched whistling or sucking noise from the engine bay at idle. A definitive test is to try removing the oil filler cap while the engine is running; if there is extreme suction holding the cap down, the PCV diaphragm has failed.
   Typical fix: Replace the entire PCV valve assembly. It is located in the engine valley under the supercharger, making replacement moderately labor-intensive. This is often done preventatively during an intercooler or carbon cleaning job.
   Est. part cost: $150-$250

Rare But Worth Checking

• Faulty Fuel Injector: → Shop Fuel Injector Less common than ignition issues, but a fuel injector can become clogged or fail electronically, causing an improper fuel mixture in cylinder 6. This can sometimes be diagnosed by swapping injectors between cylinders, but this is a much more involved job than swapping coils.
• Low Compression: A mechanical engine issue, such as worn piston rings, a damaged cylinder wall, or a problem with a valve or valve seat, can cause a loss of compression in cylinder 6. This results in a persistent misfire that does not resolve with ignition or fuel system parts and requires a compression and leak-down test to confirm.
• Clogged Catalytic Converter: A failing or clogged catalytic converter on Bank 2 (the driver's side) can create excessive exhaust backpressure, leading to misfires on cylinders 4, 5, and 6. This is often a result of long-term misfires dumping unburnt fuel into the exhaust.

Diagnosis Steps

1. Read the codes with an OBD-II scanner to confirm P0306 and check for any other codes, like P130A or P0300.
🎬 Watch: A step-by-step guide to diagnosing these 3.0T misfire codes.
2. Locate cylinder 6 on the 3.0T engine: it is on the driver's side, closest to the windshield/firewall.
3. Perform an 'ignition swap test'. Swap the ignition coil from cylinder 6 with the coil from cylinder 5 (the middle cylinder on the same side).
4. Clear the codes and run the engine. If the misfire code moves to P0305, the ignition coil is faulty and needs replacement.
5. If the code remains P0306, the coil is likely good. Next, inspect the spark plug. Remove the plug from cylinder 6 and check for wear, fouling, or damage. A white/pink crusty deposit indicates a coolant leak. Replace if necessary. It's best to replace all six plugs at once.
6. If new plugs and coils do not fix the issue, investigate common platform-specific causes. Listen for a high-pitched whistling sound at idle. If heard, perform the 'oil cap test': with the engine running, try to remove the oil cap. If it's held on by strong suction, the PCV valve has failed.
7. Check for unexplained coolant loss in the expansion tank. If the level is dropping with no visible external leaks, suspect a leaking supercharger intercooler. This is a serious issue that requires professional diagnosis.
8. If misfires occur mainly under heavy load or high RPM, suspect carbon buildup on the intake valves. This requires a borescope for visual confirmation.
9. If all else fails, the issue may be a faulty fuel injector or a mechanical engine problem (low compression), which will require more advanced diagnostics like a compression test or fuel injector flow test.

Parts You'll Likely Need

• Ignition Coil (OEM #06E905115G) — This is the most common cause of a single-cylinder misfire on the 3.0T engine. The part number 06E905115G supersedes previous versions ending in A, B, C, D, E, and F.
  Trusted brands: Bosch, NGK, Eldor, Audi Genuine
  OEM price range: $50-$80
  Aftermarket price range: $35-$60
• Spark Plug (OEM #NGK PFR8S8EG) — A worn or fouled spark plug is the second most likely cause. They are a regular maintenance item.
  Trusted brands: NGK, Bosch
  OEM price range: $20-$30
  Aftermarket price range: $15-$25
• PCV Valve / Oil Separator (OEM #06E103547Q) — A common failure on the 3.0T engine that creates a vacuum leak, leading to misfires. Part number 06E103547Q is a common version, but several revisions exist (e.g., F, AC, AF, AH). Verify the correct part for your specific VIN.
  Trusted brands: Audi Genuine, Hengst
  OEM price range: $200-$250
  Aftermarket price range: $150-$200
• Supercharger Intercooler Core — If the vehicle is losing coolant with no external leaks, a failed intercooler core inside the supercharger is a likely cause of the misfire.
  Trusted brands: Audi Genuine, Mahle
  OEM price range: $450-$650
  Aftermarket price range: $180-$500

Related Codes That Often Appear With This One

• P130A — This Audi-specific code means 'Cylinder Disabling' or 'Hide Cylinder'. The ECM sets this code as a protective measure when it detects a persistent, damaging misfire on a cylinder. It shuts off fuel to that cylinder to prevent damage to the catalytic converter. You must fix the root cause of the P0306 misfire to clear P130A.
• P0300 — This code means 'Random/Multiple Cylinder Misfire'. If you see this along with P0306, it indicates other cylinders are misfiring too. This often points to a systemic issue like a large vacuum leak (bad PCV), widespread carbon buildup, or a fuel delivery problem affecting the entire engine.
• P0305 — A misfire on cylinder 5, which is adjacent to cylinder 6 on the same bank. Seeing both codes together could point to an issue affecting the entire driver's side bank, such as a clogged catalytic converter for Bank 2 or severe carbon buildup in the intake manifold runners for those cylinders.

Technical Service Bulletins (TSBs) & Recalls

• NHTSA bulletin from Pass 1, also cited as TSB 2033768. It notes that a cylinder misfire fault (P0301-P0306) may be stored with DTC P130A ('Cylinder Disabling'). The TSB is informational and directs the technician to contact the Audi Technical Assistance Center (TAC) for further instructions before proceeding with repairs, suggesting a known but complex issue.

Platform-Specific Known Issues

• A Technical Service Bulletin (TSB 2033768/1) exists for misfires accompanied by a P130A 'Cylinder Disabling' code, indicating this is a known issue that requires special attention, directing dealers to contact Audi's technical support.
• Forum users on Ross-Tech and Audizine specifically mention that carbon buildup on the 3.0T can disproportionately affect airflow to cylinders 5 and 6, causing high-RPM misfires.
• The placement of the PCV valve underneath the supercharger makes its replacement unusually labor-intensive for what is a common wear item on many other engines, leading to high repair quotes as noted by owners on Reddit.

Mechanic-Grade Diagnostic Values

• Low-Pressure Fuel Pump (LPFP) Feed Pressure — expected: Approximately 4 to 6 bar (58 to 87 PSI).. Failure: Pressure dropping below this range, especially under load, will starve the High-Pressure Fuel Pump (HPFP).
• High-Pressure Fuel Pump (HPFP) Rail Pressure — expected: Up to 200 bar (2,900 PSI) under load.. Failure: Significantly lower pressure than requested by the ECM, often triggering code P0087.
• Live Misfire Count per Cylinder — expected: The counter for each cylinder should remain at or near zero at idle and under normal load.. Failure: A rapidly increasing count for cylinder 6 confirms an active misfire, even if it's intermittent.
• Mode $06 Misfire Data — expected: Near-zero counts for Test IDs $A2-$AC (each corresponding to a cylinder).. Failure: Elevated counts for the cylinder corresponding to cylinder 6 (e.g., Test ID $A7) can indicate misfires that are not yet severe enough to trigger a CEL.

Hidden / Shadow Codes Worth Checking

• P130A: Audi-specific code for 'Hide Cylinder' or 'Cylinder Disabling'. The ECM actively shuts down the fuel injector for a cylinder to prevent catalytic converter damage from a persistent misfire. (see via Standard OBD-II scanner, VCDS, ODIS.)

Scan Tool Commands That Help

• VCDS (VAG-COM): Engine -> Measuring Blocks -> Groups 015 and 016 — To monitor the live misfire counters for each cylinder. Group 015 shows cylinders 1-3, and Group 016 shows cylinders 4-6. This is essential for confirming the misfire is on cylinder 6 and observing under what conditions (idle, load, cold/hot) it occurs.
• VCDS (VAG-COM): Engine -> Adv. Meas. Values — On newer UDS-based controllers, this is used instead of Measuring Blocks to select and graph individual parameters like 'Misfire sum' and misfire counters for each cylinder.
• ODIS (Dealer Tool): Guided Fault Finding (GFF) — When basic diagnostics fail, GFF provides a step-by-step test plan based on the specific fault code and vehicle data, which can be crucial for complex electrical or intermittent issues.

Wiring & Ground Locations

• N84 — The fuel injector for cylinder 6.. This is the specific component identifier for the cylinder 6 fuel injector. It receives its signal from the Engine Control Module (J623) via the 105-pin connector (T105). Problems with this component or its wiring can cause a P0306.
• Engine Ground Strap — A key ground strap is located on the right (passenger) side of the engine compartment, connecting the engine block to the frame rail, often near the alternator.. A loose or corroded main engine ground can cause a variety of electrical issues, including weak spark from the ignition coils, leading to intermittent and hard-to-diagnose misfires on any cylinder.
• J623 — Engine Control Module (ECM), located in the plenum chamber (under the plastic cowl near the base of the windshield).. This is the computer that detects the misfire and stores the P0306 code. In very rare cases, a failure of the ignition coil driver circuit within the ECM itself can cause a persistent misfire on a single cylinder.

Real Owner Repair Stories

• AudiWorld Forums User (2012 Audi S4 3.0T (C7 platform equivalent to Q5)) — EPC light on, rough running, poor acceleration, P0305 (Cylinder 5 Misfire).
  ❌ Tried (didn't work) Replacing spark plugs, Replacing ignition coils
  ✅ What actually fixed it The supercharger was removed and a pressure test revealed a fine mist of coolant leaking from one of the internal intercoolers. Replacing the two intercooler cores inside the supercharger assembly resolved the misfire.
• AudiWorld Forum User (Audi Q7 3.0T (year not specified)) — Persistent P0306 misfire, especially under load.
  ❌ Tried (didn't work) Ignition coil replacement, Spark plug replacement
  ✅ What actually fixed it The thermostat was failing, causing the engine to run slightly out of its optimal temperature range. This subtly affected the air/fuel mixture enough to cause a consistent misfire on one cylinder under load. Replacing the thermostat and water pump resolved the P0306 code.
• Reddit User r/MechanicAdvice (2016 Audi S5 3.0T) — Misfire at lower RPM and stuttering at wide-open throttle after major service.
  ❌ Tried (didn't work) Replacing supercharger intercoolers, Carbon cleaning, Replacing all fuel injectors, Replacing PCV valve
  ✅ What actually fixed it The user's post was a request for help and did not have a final resolution, but it highlights a complex case where a misfire appeared *after* major work (carbon cleaning, intercooler replacement), suggesting potential issues like debris in an injector, a damaged vacuum line not found by a smoke test, or a wiring harness issue.

"I Checked Everything" — The Actual Cause

• A failed check valve within the PCV breather hose assembly is a known issue on some 3.0T engines. This failure will not present as a typical vacuum leak that an intake smoke test would find. Instead, under boost, pressure is forced back into the crankcase, which can disrupt normal operation and cause a rough idle and misfires. The diagnosis requires removing the specific hose and testing the check valve's one-way function directly, not by performing a smoke test on the intake manifold.

When the Usual Fixes Don't Work

• While the vast majority of P0306 codes are fixed with ignition components (coils and plugs), there are documented cases where the root cause is more complex. In one instance, a persistent misfire under load was only resolved after replacing a failing thermostat that was causing the engine to run slightly out of its optimal temperature range, affecting the air-fuel mixture. In another case, after ignition parts failed to fix a misfire, the ultimate culprit was found to be leaking supercharger intercoolers dripping coolant onto the intake valves for that cylinder bank, a diagnosis which required removing the supercharger to confirm.

OEM Part Supersession History

• 06E905115A/B/C/D/E/F → 06E905115G (or later) — Ongoing revisions by Audi to improve the reliability and longevity of the ignition coils and prevent premature failure.
  Heads up: While older revisions may physically fit, it is always best practice to use the latest available part number for replacements. Mixing different revisions is not ideal.
• 06E103547C/F/Q → 06E103547AC (or later) — The PCV valve (oil separator) has been updated multiple times to address issues with the diaphragm tearing and to modify crankcase pressure regulation to reduce oil consumption.
  Heads up: Some later revisions changed the internal pressure regulation (e.g., from 30 mbar to 150 mbar). Using a PCV with the wrong pressure spec for your engine's software can cause oil consumption or seal issues. It is critical to match the part to the vehicle's VIN.
• 06E145621E, 06E145621F, 06E145621R → 06E145621S — Revisions to the supercharger intercooler cores to improve durability and prevent internal coolant leaks.
  Heads up: Ensure you are purchasing the latest revision. Some part numbers may not fit later model year vehicles within the C7 generation (e.g., 2016+ A6/A7), so VIN confirmation is crucial.

Model Year Variations Within This Range

• 2013-2015 (C7 Platform): The 3.0T engine in this period uses only direct injection. This makes it more susceptible to heavy carbon buildup on the intake valves as a cause for misfires compared to the C7.5 generation (2016+) engine, which added multi-port injection (MPI) that sprays fuel on the back of the valves, keeping them clean.