P0442 on 2008-2013 BMW M3: EVAP Small Leak Causes and Fixes

What's Unique About the 2008-2013 BMW M3

Unlike many vehicles that use engine vacuum to test the EVAP system, BMWs of this era, including the E9x M3, use a Diagnostic Module for Tank Leakage (DMTL) pump. This electric pump actively pressurizes the fuel system to check for leaks, often when the car has been parked for some time, as specific temperature and fuel level conditions must be met. This is why the check engine light may appear seemingly at random, hours after driving or even overnight. The terminology is also unique: the purge valve in the engine bay is called the 'fuel tank vent valve', and the traditional vent valve is integrated into the DMTL pump assembly itself, sometimes called a changeover valve.

Symptoms You May Notice

• Service Engine Soon (Check Engine) light is on
• An 'Increased Emissions' warning message may appear in the instrument cluster
• A 'Tighten Gas Cap' or 'Check filler cap' message may appear, sometimes before the P0442 code is set
• A faint fuel smell near the rear of the car (this is uncommon)
• No whoosh of pressure being released when opening the gas cap after driving

Most Likely Causes

1. Worn or Loose Gas Cap 🔴 High Probability → Shop Fuel Tank Cap The rubber O-ring on the gas cap is a simple wear-and-tear item that can dry out, crack, and lose its sealing ability over time. It's the most common and easiest fix for a P0442 code.
   How to confirm: First, ensure the cap is tightened until it clicks. Remove the cap and inspect the rubber seal for any visible cracks, stiffness, or damage. If the seal looks worn or the car has high mileage, replacement is a cheap and effective diagnostic step.
   Typical fix: Replace the gas cap with a new OEM or high-quality aftermarket part. After replacing, you may need to clear the code with a scan tool.
   Est. part cost: $20-$45
2. Faulty Fuel Tank Vent Valve (Purge Valve) 🟡 Medium Probability → Shop Fuel Tank This solenoid valve is located under the intake plenum in the hot engine bay and cycles frequently. Over time, it can get stuck partially open or fail to seal completely, creating a small leak path. A failure can also cause rough idle, especially after refueling.
   How to confirm: With the engine off, disconnect the valve and try to blow through it. It should be completely closed and allow no air to pass. A smoke test is the definitive method, as smoke will pass through a leaking valve. A BMW-specific scan tool can also actuate the valve to test its function. A resistance check across the two pins should yield a reading of approximately 28 Ohms.
   Typical fix: Replace the fuel tank vent valve. This requires removing the intake plenum 🎬 See this step-by-step guide for replacing the vent valve. for access. It is a common DIY job.
   Est. part cost: $60-$110
3. Failed DMTL Pump 🟡 Medium Probability → Shop Evaporative Emissions System Leak Detection Pump The Diagnostic Module for Tank Leakage (DMTL) contains a small electric motor and a vent valve. The motor can wear out and fail, or the internal valve can leak. Owners on M3 and other E9x forums have reported replacing this part to solve EVAP codes.
   How to confirm: Diagnosis often requires a BMW-specific scan tool to run the DMTL test cycle. A key symptom 🎬 Watch: A deep dive into diagnosing the BMW DMTL system. is no longer hearing the faint buzzing sound from the rear driver's side wheel well area shortly after shutting off the car. A smoke test is the most common professional method; if the system has no other leaks but fails the pressure test, the DMTL pump itself is the likely culprit.
   Typical fix: Replace the DMTL pump assembly. It is located behind the rear driver's side wheel liner, attached to the charcoal canister, and is accessible by removing the wheel and liner.
   Est. part cost: $85-$220
4. Cracked or Disconnected EVAP Hoses ⚪ Low Probability Plastic and rubber hoses become brittle with age and exposure to heat cycles. A known issue on the E9x platform is the fuel tank breather hose rubbing against the chassis where it passes into the wheel well, eventually creating a small hole. Rodent damage has also been reported, with mice chewing through lines in the wheel well area.
   How to confirm: A thorough visual inspection of all accessible EVAP lines is a start. The definitive method is a smoke test, which will cause smoke to visibly escape from any cracks or holes in the lines.
   Typical fix: Replace the damaged section of hose. In some cases, a durable, fuel-safe patch like JB Weld and self-sealing silicone tape can be used for small holes if the hose is in a difficult-to-access location.
   Est. part cost: $30-$150

Rare But Worth Checking

• Cracked Charcoal Canister: → Shop Vapor Canister The canister itself can develop hairline cracks from age or impact from road debris, creating a leak. This is usually found only with a smoke test and often requires replacing the DMTL pump at the same time as they are connected.
• Leaking Fuel Tank Filler Neck: → Shop Fuel Tank Rust or corrosion around the area where the filler neck meets the tank can cause a small leak, though this is less common on the E9x M3.

Diagnosis Steps

1. Check the gas cap. Ensure it is tight and clicks. Remove it and inspect the rubber seal for cracks or damage. If it's old or worn, replace it as a low-cost first step. This solves a high percentage of P0442 issues.
2. Clear the codes and drive the vehicle for a few days. The EVAP monitor runs under specific conditions (fuel level between 15-85%, specific ambient temperatures, after the car has sat), so it may take time for the light to return. If it does not return after a week, the loose or faulty cap was likely the issue.
3. If the code returns, a professional smoke test is the most effective next step. This test can also be performed by a DIYer with an automotive smoke machine.
🎬 Watch: How to perform a professional EVAP leak diagnosis.
4. To perform a smoke test, connect the smoke machine's output hose to the EVAP system service port, or disconnect the line from the fuel tank vent valve (purge valve) in the engine bay and introduce smoke there.
5. With the system filled with smoke, visually inspect all EVAP components for leaks. Pay close attention to the fuel tank vent valve (under the intake plenum), the DMTL pump and charcoal canister area (rear driver's side wheel well), all hose connections, and the gas cap seal.
6. If no smoke is visible but the system does not hold pressure, the fault may be internal to the fuel tank vent valve or the DMTL pump's integrated valve.
7. Once the leak is located, replace the faulty component. There are many DIY videos available for replacing the most common parts like the vent valve and DMTL pump.

Parts You'll Likely Need

• Gas Cap (OEM #16117222391) — This is the most frequent and easiest fix. The seal wears out over time, causing a leak that the system detects.
  Trusted brands: Genuine BMW, Blau
  OEM price range: $30-$45
  Aftermarket price range: $15-$25
• Fuel Tank Vent Valve (Purge Valve) (OEM #13907838281) — Located in the engine bay under the plenum, this valve controls the flow of vapors to the engine. It can fail to seal properly, causing a persistent small leak. Bosch is the original equipment manufacturer.
  Trusted brands: Bosch (OEM), Genuine BMW
  OEM price range: $65-$110
  Aftermarket price range: $40-$70
• DMTL Pump (Leak Detection Pump) (OEM #16137193479) — This pump pressurizes the system for leak testing and contains an integrated vent valve. Failure of the pump motor or its internal valve will cause EVAP codes. It is located behind the driver-side rear wheel liner. Bosch is the OEM for this part.
  Trusted brands: Bosch (OEM), Genuine BMW
  OEM price range: $150-$220
  Aftermarket price range: $85-$130

Related Codes That Often Appear With This One

• P0456 — P0456 indicates a 'very small leak,' while P0442 indicates a 'small leak.' They point to the same set of potential failures, just a different leak rate detected by the system. It's common to see one or the other for the same root cause.
• 2A15 / 2A16 — These are BMW-specific fault codes that correspond directly to small EVAP leaks detected by the DMTL system, essentially the manufacturer's version of P0442.

Technical Service Bulletins (TSBs) & Recalls

• While no TSBs are specific to the E9x M3 for P0442, BMW has issued extended warranties for the fuel tank vent (purge) valve on other contemporary models (e.g., SIB 01 03 24, SIB 01 02 24) for similar issues, highlighting the part's tendency to fail across the brand.

Platform-Specific Known Issues

• Fuel Breather Hose Chafing: On E9x platform vehicles, the fuel breather hose that runs from the charcoal canister area toward the engine can rub against the body chassis where it passes through an opening near the wheel well. Over time, this can wear a small hole in the plastic line, causing a persistent small leak. This is often only found with a smoke test. Some owners have successfully patched the hole with JB Weld and silicone tape as a temporary fix.

Mechanic-Grade Diagnostic Values

• Fuel Tank Vent Valve (Purge Valve) coil resistance — expected: Approximately 28 Ohms (e.g., 28.1 Ω). Failure: A significantly higher resistance reading (e.g., 190+ Ω) or an open circuit indicates a failed coil.
• DMTL pump motor operating current during reference measurement — expected: 20-30 mA. Failure: The DME compares the current draw during the leak test to this reference value. A significant deviation indicates a leak.

Hidden / Shadow Codes Worth Checking

• 2A15: DMTL, system fault: fine leak detected. This is the direct BMW-specific equivalent of the generic P0442 code. (see via BMW-specific scan tools like ISTA, INPA, or advanced aftermarket scanners (e.g., Foxwell, Autophix).)
• 2A16: DMTL, system fault: leak (greater than 0.5mm) or gas cap open. Often appears alongside 2A15. (see via BMW-specific scan tools like ISTA or INPA.)
• 2A18 / P240A: DMTL pump heater circuit open. This points specifically to an issue with the heater element inside the DMTL pump assembly or its wiring, not a system leak. (see via BMW-specific scan tools.)
• 2B3A: DMTL system fault. A general fault code indicating the DMTL pump needs to be replaced. (see via BMW-specific scan tools.)

Scan Tool Commands That Help

• ISTA (BMW Dealer Software): EVAP system test plan / DMTL leak diagnosis pump activation — This is the guided diagnostic procedure a dealer would use. It automatically runs a sequence to seal the system, run the DMTL pump, and analyze the result to confirm a leak and suggest next steps. It can command the vent valve closed and activate the pump to find leaks.
• INPA (BMW Factory Software): DMTL Test / End of Line Test — Found within the engine control module section (e.g., MSV70), this allows a technician to manually trigger the DMTL pump test cycle to confirm if the pump is functional and to check for leaks without waiting for the car's automatic monitor to run.
• Advanced Aftermarket Scan Tool: Activation Test / Bidirectional Control for EVAP Vent Valve and Purge Valve — Used during a smoke test to command the system's valves. The vent valve (part of the DMTL pump) is normally open and must be commanded closed to seal the system for the smoke test. The purge valve can be commanded open to check its function.

Wiring & Ground Locations

• X1714 / X17140 — The 4-pin electrical connector on the DMTL pump itself, located behind the driver-side rear wheel well liner.. This is the primary connection point for testing the DMTL pump's power and ground signals. A forum post details the pinout for E9x models: Pin 1 (Brown/Blue) is the pump motor ground switch from the DME, Pin 2 (Black/Red) is the heater ground, Pin 3 (Black/Green) is the valve ground, and Pin 4 (Red/White) is the power supply from the DME relay. Wiring breaks have been reported near this connector.

Real Owner Repair Stories

• Bimmerpost user 'srohang1' (BMW E9x (specific model not stated, but platform-relevant)) — P0442 code.
  ❌ Tried (didn't work) Replaced gas cap., Inspected hose under throttle body.
  ✅ What actually fixed it During a smoke test, the user found a hole chewed in the fuel breather hose by a mouse that had made a nest above the wheel well liner. The user patched the hole with JB Weld and self-sealing silicone tape to fix the leak.
• Bimmerpost user 'Efthreeoh' (2006 BMW 330i (E90)) — P0442 code and a 'loose gas cap' symbol on the dash.
  ❌ Tried (didn't work) Repeatedly clearing the code with a scan tool.
  ✅ What actually fixed it The car was under warranty, and the dealer performed a smoke test. They discovered a mouse had bitten a hole in one of the EVAP lines coming off the fuel filler hose that goes to the EVAP canister. The dealer replaced the damaged line.
• Bimmerpost user 'MFL' (BMW E9x M3) — Started with 'Tighten gas cap' warning, progressed to P0442 'Increased Emissions' and SES light.
  ❌ Tried (didn't work) Replacing the gas cap., Replacing a Bank 2 O2 sensor that threw a separate code., Replacing the DMTL pump after noticing it was no longer audible after parking.
  ✅ What actually fixed it The user's post ends with them still trying to diagnose the issue after replacing multiple parts. The final step suggested was a smoke test. This story is included as a cautionary tale of replacing parts without a definitive diagnosis, as even after replacing the most common culprits (gas cap, DMTL pump), the issue persisted.

"I Checked Everything" — The Actual Cause

• In a forum discussion, a user with a 2A15/2A16 fault (the BMW equivalent of P0442) stated that after performing a smoke test and finding no visible leaks or damaged hoses, they replaced the DMTL pump as a last resort. This fixed the issue, indicating the failure was internal to the DMTL pump (likely the integrated changeover valve not sealing properly), which a smoke test would not visually reveal as an external leak.

OEM Part Supersession History

• 16136752551, 16136764191 → 16137193479 — The DMTL pump has been redesigned and superseded multiple times by BMW to improve reliability.
  Heads up: The newest part number, 16137193479, is the correct replacement for all E9x M3 models and is backward compatible.

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 — Considered a critical preventative maintenance item. Wear can be significant by 60,000-80,000 miles, regardless of driving style, due to tight factory clearances and oil specifications. Failure is catastrophic to the engine.
• Throttle Body Actuator Failure 🔴 High — A very common failure point. The internal plastic gears wear out and/or the electronics fail, causing the car to enter limp mode with DSC and EML lights. Failure is common between 50,000 and 80,000 miles. It is recommended to replace both actuators at the same time.
• Idle Control Valve (ICV) Failure 🟠 Medium — A common issue that causes a rough, surging, or erratic idle, especially when cold. Can eventually trigger fault codes and limp mode. Often requires replacement as cleaning is not always effective. (Ref: A service bulletin (13-05-08) was issued, which may have led to a recall or warranty extension in some cases.)
• Main Bearing Failure 🔴 High — A less discussed but emerging issue that is potentially more common than rod bearing failure on higher mileage S65 engines. The #1 main bearing is particularly susceptible to wear, leading to oil starvation and catastrophic engine seizure.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, buying used parts is generally not recommended. The primary failure components (gas cap seal, purge valve solenoid, DMTL pump motor) are all wear-and-tear items. A used part from a donor vehicle is likely to have similar age and wear, offering little to no long-term reliability.

What to inspect on the donor part:

• Not applicable as used parts are not advised for this repair.

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

• Gas Cap: While aftermarket caps exist, many owners report that only a Genuine BMW cap (PN 16117222391) will provide a perfect seal and definitively solve the issue. The cost difference is minimal and worth the peace of mind.

Aftermarket brands forum-validated for this vehicle:

• Bosch: Bosch is the Original Equipment Manufacturer (OEM) for both the Fuel Tank Vent Valve (Purge Valve) and the DMTL pump. Buying the Bosch-branded part is identical to the Genuine BMW part but without the BMW logo and often at a significantly lower price.

Brands owners have reported issues with on this vehicle:

• No-name or unbranded parts from online marketplaces. For critical emissions components like valves and pumps, sticking with the OEM (Bosch) or Genuine BMW is the safest path to ensure proper function and avoid repeat failures.

Real Owner Stories

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

Related OBD-II Codes

• P0440 — A general EVAP system malfunction code that often appears when the system fails the initial leak detection tests shared by P0442.
• P0441 — Related to incorrect purge flow; often triggered by the same faulty fuel tank vent valve (purge valve) that causes P0442.
• P0455 — Indicates a large EVAP leak; often the result of a gas cap being completely loose or a total failure of the same components (DMTL pump or vent valve) that cause the P0442 small leak.
• P0456 — Indicates a very small EVAP leak; this is the companion code to P0442 and is triggered by the same root causes like a slightly cracked gas cap O-ring or a pinhole in a breather hose.

Frequently Asked Questions