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DTC codes / BMW codes / P1447

P1447 · BMWDiagnostic Module Tank Leakage DM-TL Pump Too High During Switching

P1447 on BMW vehicles means the Diagnostic Module Tank Leakage (DM-TL) pump reported a current or pressure reading that was too high during its switching phase, which is the moment the module toggles the pump to verify the evaporative system can hold a vacuum or pressure. The engine control module sets this code when the pump's electrical feedback or the resulting pressure change exceeds the expected window, indicating a restriction, a stuck pump, or a wiring fault rather than a simple leak.

SystemPowertrain
Code typeBMW specific
SeverityMedium
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • Illumination of the Check Engine Light, often with no other noticeable symptoms.
  • A slight fuel odor around the rear of the vehicle if the tank vent system is restricted.
  • Rough idle or hesitation in rare cases where the purge system is affected by the same fault.
  • Failed emissions inspection due to the stored code and incomplete evaporative monitor.
  • Intermittent code setting after refueling or during temperature swings when the tank pressure changes.
  • No driveability complaints in most cases because the DM-TL pump only runs during the self-test.

Common causes, most likely first

  1. Faulty DM-TL pump assembly, including a stuck or seized pump motor that draws excessive current.
  2. Restricted or pinched evaporative emission hose between the tank, DM-TL module, and charcoal canister.
  3. Corroded, chafed, or shorted wiring in the DM-TL pump circuit, including the ground and power supply.
  4. Failed fuel tank vent valve that stays closed and prevents the pump from switching pressure correctly.
  5. Contaminated or saturated charcoal canister restricting flow and forcing the pump to work too hard.
  6. Engine control module software or internal driver fault in the DM-TL output stage, though this is less common.
  7. A blocked fuel tank pressure sensor port or a skewed sensor that misreports the switching pressure.

How to diagnose and fix it

  1. Connect a BMW-capable scan tool and read the DM-TL live data during the evaporative system self-test to confirm the pump current and pressure readings.
  2. Visually inspect all evaporative hoses and the charcoal canister for cracks, pinches, or disconnected lines, and check the fuel cap seal.
  3. Measure resistance and supply voltage at the DM-TL pump connector, then compare with BMW specifications to rule out wiring and pump motor faults.
  4. Command the fuel tank vent valve open and closed with the scan tool and listen for a click while checking for a change in tank pressure.
  5. Remove the DM-TL pump and bench-test it for free rotation and current draw, replacing it if it binds or exceeds the specified amperage.
  6. Check the fuel tank pressure sensor reading against a known-good gauge and clean or replace the sensor if the value is implausible.
  7. After repairs, clear the fault memory and run the evaporative system monitor to completion to confirm the code does not return.

What the DM-TL pump test really checks

  • A P1447 is often misdiagnosed as a simple large leak, but the 'too high during switching' wording points to a restriction or electrical fault rather than an open tank.
  • The DM-TL pump only runs for a few seconds during the self-test, so a pump that binds when cold may pass a static resistance check and still set the code.
  • A saturated charcoal canister from overfilling the fuel tank is a frequent hidden cause because it restricts flow and forces the pump current above the expected threshold.
  • Corrosion inside the DM-TL pump connector can create a high-resistance path that mimics a failing pump, so always back-probe the circuit under load before replacing parts.
  • This code can be set by a fuel tank vent valve that sticks closed, which prevents the pressure from equalizing and makes the pump appear to be working too hard.

Can I keep driving with P1447?

You can usually continue driving with P1447 because the fault affects only the evaporative emissions self-test and does not impair engine performance, but avoid topping off the fuel tank and schedule diagnosis soon to prevent a small issue from becoming a costly canister or pump replacement.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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