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P043FEvaporative Emission System Leak Detection Reference Orifice High Flow

The engine computer detected too much air flowing through the EVAP leak-detection pump's reference orifice during a self-test, so it cannot establish a valid baseline for leak checking.

Definition

On vehicles that use a leak detection pump (common on Toyota, Nissan, and some European models), the PCM runs a key-off EVAP self-test that first pulls vacuum through a precision 0.02-inch reference orifice to establish a baseline pressure reading. P043F sets when the pressure measured across that orifice indicates higher-than-expected flow, meaning the orifice is enlarged, cracked, or bypassed, and the PCM cannot trust its leak-test baseline. The only symptom is usually an illuminated MIL with no driveability change, but the EVAP monitor will not complete, which causes an emissions-inspection failure in states that require monitor readiness.

Common causes

  • Cracked or enlarged reference orifice inside the leak detection pump (canister pump module) assembly
  • Faulty EVAP pressure sensor inside the pump module giving a skewed baseline reading
  • Failing leak detection pump motor that cannot develop proper vacuum across the orifice
  • Damaged or leaking hose/seal between the pump module and the charcoal canister
  • Debris or physical damage to the canister vent path altering flow through the module
  • Rarely, wiring or PCM issues corrupting the pressure sensor signal

Common misdiagnoses

  • Gas cap replaced even though this code is about the test hardware, not a leak
  • Charcoal canister replaced when the fault is in the attached pump module
  • Purge valve/solenoid replaced, which plays no role in the reference-orifice phase
  • EVAP hoses smoke-tested and replaced when the reference measurement itself is faulty

Troubleshooting steps

  1. 1.Read freeze frame and check for companion codes

    Codes like P043E, P2401, P2402, or P2419 alongside P043F strongly point to the leak detection pump module assembly itself.

  2. 2.Locate the leak detection pump module

    It is typically mounted on or near the charcoal canister at the rear of the vehicle; the reference orifice, pump, vent valve, and pressure sensor are one serviceable assembly on most applications.

  3. 3.Run the EVAP system test with a scan tool

    Command the pump on and watch the EVAP pressure PID; a healthy reference check pulls a stable baseline vacuum, while a reading that stays near atmospheric indicates excess flow through the orifice.

  4. 4.Inspect hoses and connections at the canister

    Look for cracked, disconnected, or oil-soaked hoses between the pump module, canister, and vent line that could bypass the orifice.

  5. 5.Replace the pump module if the baseline is out of range

    Because the orifice and pressure sensor are integrated, an out-of-spec reference reading with intact hoses is fixed by replacing the canister pump module assembly.

  6. 6.Clear the code and confirm monitor completion

    Let the vehicle sit key-off (the test typically runs about 5 hours after shutdown on Toyota) or force the EVAP monitor with the scan tool and verify the code does not return.

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