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DTC codes / BMW codes / P1446

P1446 · BMWDiagnostic Module Tank Leakage DM-TL Pump Control Circuit Signal High

This code means the BMW engine computer detected an abnormally high voltage on the control circuit for the Diagnostic Module Tank Leakage (DM-TL) pump, which is the pump that pressurizes the fuel tank for evaporative emissions testing. The computer expects a specific voltage range when it commands the pump on or off, and a signal that stays too high indicates a short to voltage or an open circuit in the pump control wiring.

SystemPowertrain
Code typeBMW specific
SeverityLow
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 may be present if the tank leak diagnostic cannot run and a small leak goes undetected.
  • In some cases, the engine may run slightly rough or have a hard start after refueling due to evap system interference.
  • The remote start or fuel door lock may be inoperative on models where the DM-TL pump shares a circuit with those functions.
  • No driveability complaints are typical, but the vehicle will fail an emissions inspection if the light is on.
  • A stored code P1446 may be accompanied by other evap-related codes if the pump circuit fault affects other diagnostics.

Common causes, most likely first

  1. A short to voltage in the wiring between the DM-TL pump and the engine control module (ECM).
  2. An open circuit or high resistance in the pump control wire, often due to a broken wire or corroded connector.
  3. A failed DM-TL pump assembly, where the internal control circuit has failed and is sending a high voltage signal back to the ECM.
  4. A faulty engine control module (ECM) driver for the pump control circuit, though this is less common.
  5. Water intrusion or corrosion in the connector at the DM-TL pump or at the ECM, causing a high voltage signal.
  6. A pinched or chafed wire harness near the fuel tank or under the rear seat where the pump is mounted.

How to diagnose and fix it

  1. Use a scan tool to clear the code and verify it returns; then check for any related evap codes that may indicate a different root cause.
  2. Visually inspect the DM-TL pump connector and wiring for corrosion, damage, or loose pins, especially at the pump and where the harness passes near the fuel tank.
  3. Disconnect the DM-TL pump connector and measure the voltage on the control circuit with the key on; compare to the manufacturer's specification to check for a short to voltage.
  4. Check the resistance of the pump control wire from the ECM connector to the pump connector to rule out an open circuit or high resistance.
  5. If the wiring and connectors are good, test the DM-TL pump by applying power and ground directly to verify it operates; replace the pump if it fails.
  6. If the pump and wiring check out, inspect the ECM connector for corrosion or damage, and if necessary, test the ECM driver circuit with a known-good module.
  7. After repairs, clear the codes and perform a drive cycle that includes the conditions for the tank leak diagnostic to run, then verify no codes return.

Common misdiagnosis traps for P1446

  • A short to voltage in the DM-TL pump control circuit often mimics a failed pump, so technicians who replace the pump without checking the wiring frequently see the code return.
  • The DM-TL pump on BMW models is part of the fuel tank leak diagnostic module and can be damaged by water intrusion from a clogged sunroof drain or rear body seal, which is often overlooked.
  • This code can be set by a faulty fuel tank pressure sensor or a stuck vent valve that affects the pump's ability to build pressure, so the entire evap system should be inspected, not just the pump circuit.
  • On some BMW models, the DM-TL pump shares a power supply with the fuel pump, so a failing fuel pump relay or fuse can cause a high voltage signal on the control circuit.
  • A loose or corroded ground connection for the DM-TL pump can cause the pump to draw less current and the ECM to see a high voltage on the control circuit, which is often misdiagnosed as a short.

Can I keep driving with P1446?

The vehicle is safe to drive with this code because it does not affect engine performance or safety systems, but the check engine light will remain on and the vehicle will fail emissions testing. Avoid clearing the code repeatedly without diagnosis, as the underlying fault could worsen and affect other evap system functions.

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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