P0307 on 2007-2013 BMW M3: Cylinder 7 Misfire Causes and Fixes

What's Unique About the 2007-2013 BMW M3

The E9x M3's S65 is a high-revving, motorsport-derived V8. While a P0307 is often a simple fix, this engine has unique components that can be the root cause. Unlike most engines, the S65 uses two 'Ionic Current Control Modules' to detect knock and misfires by measuring the conductivity of the air/fuel mixture across the spark plug electrodes after ignition. A failing module for Bank 2 (cylinders 5-8) can cause isolated misfires like P0307. Additionally, while notorious issues like throttle body actuator failure typically cause misfires on a whole bank of cylinders, it's important to rule out the basics before suspecting these more complex, S65-specific problems.

Symptoms You May Notice

• Rough idle or engine vibrations, sometimes causing the car to shake at stops.
• Hesitation or stumbling during acceleration.
• Noticeable loss of engine power.
• Flashing or solid Check Engine Light.
• "Engine Malfunction, Reduced Power" message on the iDrive screen.
• Smell of raw fuel from the exhaust.
• Hard starting, requiring longer cranking time.

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil The high-performance, high-heat environment of the S65 engine places significant stress on ignition components, leading to eventual failure. It is a very common failure point for misfires. Some owners on forums report that only genuine OEM coils work reliably, with aftermarket versions causing persistent issues.
   How to confirm: Swap the ignition coil from cylinder 7 with another cylinder (e.g., cylinder 5). Clear the codes and run the engine. If the fault code changes to P0305, the ignition coil is confirmed to be the problem. This is the universally recommended first step. 🎬 Watch: Step-by-step spark plug and ignition coil service guide.
   Typical fix: Replace the faulty ignition coil. It is often recommended to use OEM-branded coils (Bosch, Delphi) as some aftermarket coils are known to cause issues on the S65. If one coil has failed and the others are original, it's wise to replace all 8 to prevent future misfires.
   Est. part cost: $40-$80 per coil
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug The S65 is sensitive to spark plug condition and requires periodic replacement as a maintenance item. Plugs can become fouled by fuel from a leaky injector or oil from valve cover gasket leaks, causing a weak or inconsistent spark.
   How to confirm: After confirming the coil is good, swap the spark plug from cylinder 7 with another cylinder. If the misfire code follows the spark plug, the plug is the issue. Visually inspect the plug for wear, carbon buildup, oil fouling, or incorrect gap.
   Typical fix: Replace the spark plug. If one is worn, it is best practice to replace all 8, especially if their service history is unknown. NGK is the OEM supplier for this engine.
   Est. part cost: $15-$25 per plug
3. Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector Fuel injectors can become clogged with deposits over time or fail electronically. A more serious issue on the S65 is an injector sticking open, which can wash oil from the cylinder walls, leading to catastrophic cylinder scoring and compression loss. This is a known failure pattern discussed extensively in owner forums.
   How to confirm: If swapping the coil and plug does not move the misfire from cylinder 7, the injector is the next suspect. 🎬 Watch: Common S65 engine problems you should know about. A strong smell of raw fuel is a major clue. A professional can perform a flow test, or a DIYer can listen for the injector's 'click' with a mechanic's stethoscope. Pulling the spark plug and finding it wet with fuel is another strong indicator.
   Typical fix: Replace the fuel injector for cylinder 7. Unlike many other BMW engines, S65 injectors do not require coding. Bosch is the OEM manufacturer. Given the risk of engine damage from a failed injector, some owners recommend replacing all 8 as a preventative measure.
   Est. part cost: $120-$200 per injector

Rare But Worth Checking

• Failing Ionic Current Control Module: The S65 has two of these modules, one for each cylinder bank, mounted on the valve covers. They are responsible for detecting misfires and knock. A failing module for Bank 2 (cylinders 5-8) can cause a persistent misfire on a single cylinder like P0307. A good diagnostic step is to swap the modules between banks and see if the misfire moves to Bank 1 (cylinders 1-4). They do not require programming.
• Low Engine Compression: This indicates a mechanical engine problem, such as a worn piston ring, damaged valve, or cylinder wall scoring (a known risk from a leaking injector). This is uncommon but possible and represents a worst-case scenario. A compression test and a leak-down test are required to diagnose this. Healthy compression should be in the 150-200 PSI range.
• Loose Ground Wire: A forum member on M3Post reported that a persistent P0307 misfire was caused by an engine ground wire that was not properly secured after a throttle actuator replacement. This is worth checking if recent work has been performed in the engine valley, as the ground points are located there.
• Vacuum Leak: While less common for a single-cylinder misfire, a leak in the intake manifold gasket specific to the runner for cylinder 7 could lean out the mixture and cause a misfire. This is more difficult to diagnose and may require a smoke test.

Diagnosis Steps

1. Read all fault codes with a BMW-compatible scanner. Note any codes besides P0307, especially bank-wide codes.
2. Locate Cylinder 7: It is on the driver's side of the engine (Bank 2), the third cylinder from the front bumper.
3. Swap the ignition coil from cylinder 7 with the coil from cylinder 5 (the front-most cylinder on the same bank).
4. Clear the fault codes, start the engine, and let it run for a few minutes. A short drive may be necessary. Re-scan for codes.
5. If the code is now P0305, the ignition coil is faulty and needs replacement.
6. If the code remains P0307, swap the spark plug from cylinder 7 with the one from cylinder 5.
7. Clear the codes and re-test. If the code is now P0305, the spark plug is the culprit.
8. If the code still remains P0307, the issue is likely the fuel injector, wiring, or the Ionic Current Control Module.
9. Inspect the wiring and connector for the fuel injector and ignition coil on cylinder 7 for any visible damage or looseness.
10. Consider swapping the Ionic Current Control Modules between Bank 1 (passenger side) and Bank 2 (driver side). They are located on the valve covers. If the misfire moves to a cylinder on Bank 1 (e.g., P0301-P0304), the Bank 2 module is bad.
11. If a fuel injector is suspected, listen for its operation with a stethoscope or pull the spark plug to check for excessive fuel wetness.
12. If recent engine work was done, inspect engine ground straps in the valley between the cylinder banks to ensure they are tight.
13. If all of the above steps fail, a professional diagnosis involving a compression test and leak-down test is recommended to check for mechanical engine health.

Parts You'll Likely Need

• Ignition Coil (OEM #12138657273) — This is the most common cause of a single-cylinder misfire on the S65 engine.
  Trusted brands: Bosch, Delphi, Eldor
  OEM price range: $60-$90
  Aftermarket price range: $35-$55
• Spark Plug (OEM #12120032273) — A worn or fouled spark plug is the second most common cause of a misfire. It is a standard maintenance item.
  Trusted brands: NGK (LKR8AP)
  OEM price range: $20
  Aftermarket price range: $15
• Fuel Injector (OEM #13647838440) — A clogged or failed fuel injector is a common cause if the coil and plug are good. A leaking injector is a serious risk on this engine.
  Trusted brands: Bosch
  OEM price range: $180
  Aftermarket price range: $120

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects other cylinders, a P0300 (Random/Multiple Misfire) code may appear alongside P0307.
• P0305, P0306, P0308 — If these codes for the other cylinders on Bank 2 appear with P0307, it strongly suggests a problem affecting the entire bank, such as a failing Throttle Body Actuator, Bank 2 Ionic Current Control Module, or a major vacuum leak on that bank.
• 2B3B — This is a BMW-specific code for 'Misfire with shutdown, Cyl 7', which is more specific and confirms the DME is shutting off the injector to protect the engine and catalysts.
• 2B41 — This BMW code for 'Misfire with cutout, several cylinders' often appears when an entire bank is misfiring, pointing towards a bank-wide issue rather than a single component on cylinder 7.

Platform-Specific Known Issues

• Throttle Body Actuator Failure: While not typically the cause of an *isolated* P0307, it's the most famous S65 engine issue. Failure usually results in misfires across all four cylinders of one bank (Bank 1: 1-4, Bank 2: 5-8) and puts the car in limp mode.
• Ionic Current Control Module Failure: The S65 uses these modules instead of knock sensors. A failing module can cause difficult-to-diagnose misfires that may not respond to new plugs or coils.
• Stuck-Open Fuel Injector: This is a critical failure mode on the S65. A strong smell of raw fuel accompanying a misfire is a major warning sign. A stuck-open injector can wash oil off the cylinder walls, leading to rapid cylinder bore scoring and catastrophic engine damage.

Mechanic-Grade Diagnostic Values

• Fuel Pressure (Low-Pressure System) — expected: 3.0 to 6.0 bar (43.5 to 87 PSI), variable based on DME demand.. Failure: Pressure that is consistently low, high, or does not respond to changes in engine load could indicate a failing fuel pump or sensor.
• Fuel Injector Resistance — expected: Typically 12 to 16 ohms for high-impedance injectors like those on the S65.. Failure: A reading of infinite resistance (open circuit) or near-zero resistance (short circuit). A value significantly different from the other 7 injectors also indicates a problem.
• Ignition Coil Primary Resistance — expected: While a specific ohm value for the S65 coil is not published for field testing, a functional test is preferred. A multimeter test is generally unreliable for modern coils as it cannot detect internal insulation breakdown that only occurs under high voltage load.. Failure: The definitive test is swapping the coil to another cylinder and seeing if the misfire code follows.

Hidden / Shadow Codes Worth Checking

• 2B3B: Misfire with shutdown, cylinder 7. This is a highly specific BMW fault code confirming the DME has detected a misfire on cylinder 7 and has cut fuel to that cylinder to protect the catalytic converter. (see via BMW-specific diagnostic tools like ISTA, INPA, or high-end aftermarket scanners.)
• 2B41: Misfire with cutout, several cylinders. This code often appears with other misfire codes (like 2B3B) and indicates the DME is shutting down multiple cylinders. If seen with P0307, it may point to a bank-wide issue. (see via BMW-specific diagnostic tools like ISTA, INPA, or high-end aftermarket scanners.)
• 2796: Throttle actuator test, lower stop. While not a direct misfire code, if this appears alongside bank-wide misfires (P0305, P0306, P0307, P0308), it strongly suggests a failing throttle body actuator is the root cause, not an issue with cylinder 7 itself. (see via BMW-specific diagnostic tools.)

Scan Tool Commands That Help

• ISTA/INPA: Cylinder Smooth Running Test — This function graphically displays the rotational speed contribution of each cylinder. Cylinder 7 will show a clear deviation if it is misfiring. This helps confirm the misfire is real-time and not just a stored code.
• ISTA/INPA: Fuel Injector Test — Allows for the activation of individual fuel injectors. While it doesn't measure flow, it can confirm if the injector is receiving a signal and is electronically functioning (a 'click' should be heard).
• ISTA/INPA: Ionic Current Module Test Plan — After swapping the Ionic modules between banks, this test plan can be run to check the function of the modules and confirm if the fault has moved with the suspected bad module.

Wiring & Ground Locations

• Engine Ground Straps — There are multiple ground points in the engine valley, between the cylinder banks, underneath the intake plenum. These are brown wires bolted to the engine block.. A loose or corroded ground strap, particularly one related to the Bank 2 ignition or injection system, can cause erratic behavior and persistent, hard-to-diagnose misfires on cylinders 5-8. This is especially important to check if work has recently been done in the engine valley (e.g., throttle actuator replacement).
• Cylinder 7 Ignition Coil Connector (X60002) — The 3-pin connector directly on top of the ignition coil for cylinder 7.. Testing for 12V power (Pin 3) and the signal from the DME (Pin 1) at this connector can rule out wiring issues between the DME and the coil. The center pin (Pin 2) is for the ionic current signal.
• Cylinder 7 Fuel Injector Connector (X60001) — The 2-pin connector on the fuel injector for cylinder 7, located under the fuel rail.. Checking for a pulsed signal with a noid light or multimeter during cranking can verify the DME is commanding the injector to fire. This helps differentiate a bad injector from a wiring or DME driver problem.

Real Owner Repair Stories

• M3Post forum user (E92 M3) — Persistent P0307 misfire, rough idle.
  ❌ Tried (didn't work) Replaced spark plug on cylinder 7, Replaced ignition coil on cylinder 7, Swapped ignition coils between cylinders
  ✅ What actually fixed it The owner had recently replaced the throttle body actuators. It was discovered that an engine ground wire in the valley was not properly tightened during reassembly. Securing the ground wire resolved the P0307 code.
• YouTube video by 'Vehicular DIY' (E60 M5 (S85 V10 engine, which shares the Ionic Current Module technology with the S65)) — Persistent single-cylinder misfire, reduced power, limp mode.
  ❌ Tried (didn't work) Replacing ignition coils, Replacing spark plugs, Suspecting fuel injectors
  ✅ What actually fixed it The Ionic Current Control Module for the affected bank had failed. The video demonstrates swapping the modules between banks, which caused the misfire to move to the other bank, confirming the module was the fault. The module was replaced, fixing the issue.

OEM Part Supersession History

• 12137838388 → 12137841754, then 12138657273 — BMW periodically revises ignition coil designs for improved reliability and performance.
  Heads up: While all versions are technically compatible, it is highly recommended to replace coils in full sets of 8, or at least across one entire bank (4 coils), to ensure consistent performance. Mixing old and new revisions can sometimes cause subtle performance issues.
• N/A → 13647838440 — The Bosch-manufactured fuel injector (Bosch #62418) is the consistent OEM part for the entire S65 production run.
  Heads up: There are no major revisions or incompatibilities. Ensure you are buying from a reputable source, as counterfeit injectors exist.

Model Year Variations Within This Range

• 2008-mid 2010 vs. mid-2010-2013: The material of the connecting rod bearings was changed from a copper/lead composition to a tin/aluminum one around mid-2010. This does not directly affect a P0307 diagnosis but is a critical point of knowledge for overall engine health and maintenance history.
• 2008 models: Early 2008 models had a different oil cooler and power steering pump/belt routing design compared to later models. This is unlikely to be related to a P0307 code but is a known variation within the model run.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Rod Bearing Failure 🔴 High — A widely discussed issue. Proactive replacement is commonly recommended between 60,000 and 80,000 miles, as failure can be catastrophic and often occurs with little warning. The cause is attributed to tight factory clearances and oil specifications.
• Throttle Body Actuator (TBA) Failure 🔴 High — Very common, typically failing around 50,000-70,000 miles. The failure is due to wear on internal plastic gears and failure of electronic components on the circuit board. Results in 'limp mode' and misfires across an entire cylinder bank.
• Idle Control Valve (ICV) Failure 🟠 Medium — A common issue that causes a rough, surging, or erratic idle. Failure can trigger a check engine light and limp mode. It is a single, expensive component located deep in the engine valley.
• Valve Cover Gasket Leaks 🟡 Low — Common oil leak point for many BMW engines, including the S65. Oil leaks onto the exhaust manifold causing a burning smell, and can also leak into the spark plug tubes, fouling the plugs and causing misfires.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: Used parts can be a cost-effective option for the Ionic Current Control Module, as they are generally reliable and do not require coding. A used engine wiring harness could also be considered if a specific connector or wire is damaged and cannot be repaired.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For an Ionic Module, ensure the donor car was not parted out due to a fire or major electrical issue.
• Check for clean connectors with no signs of corrosion or water intrusion.
• Verify the part number on the used component matches the one you are replacing.
• Ask the seller for the VIN of the donor car to check its history if possible.

OEM-only on this vehicle (don't cheap out):

• Ignition Coils: Many owners report issues with aftermarket coils on the S65. It is strongly recommended to use OEM (made by Delphi, Bosch, or Eldor) or Genuine BMW coils to avoid persistent misfires.
• Fuel Injectors: Given the catastrophic risk of engine damage from a leaking injector on the S65, using new, OEM Bosch injectors is the safest choice. The cost savings of a used injector do not outweigh the risk.

Aftermarket brands forum-validated for this vehicle:

• Delphi (Ignition Coils)
• Bosch (Ignition Coils, Fuel Injectors)
• NGK (Spark Plugs)

Brands owners have reported issues with on this vehicle:

• Unbranded or generic 'eBay' ignition coils. Forum consensus is that these have a very high failure rate on the S65 engine.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0305 — This code (Cylinder 5 misfire) is the primary diagnostic companion used during the 'swap test' to confirm if a coil or plug from Cylinder 7 is faulty.
• P0301 — Misfire codes for Bank 1 (P0301-P0304) may appear if the Ionic Current Control Modules are swapped during diagnosis to test for module failure.
• P0300 — Random or multiple cylinder misfires often accompany P0307 if the issue is related to the Idle Control Valve or a failing Throttle Body Actuator affecting the whole bank.
• P0302 — Misfire code that may occur if valve cover gasket leaks are fouling multiple spark plug tubes with oil.
• P0308 — Another Bank 2 misfire code that frequently appears alongside P0307 when a Throttle Body Actuator fails, affecting cylinders 5-8.

Frequently Asked Questions