P043E: Evaporative Emission System Leak Detection Reference Orifice Low Flow
What to do
Fix this one before believing any other fuel vapour leak codes. It concerns the reference the system calibrates its leak test against — so while it is faulty, every leak measurement it makes is unreliable. It is worth saying that to the garage before anyone starts replacing fuel tank parts.
The cause is often simply dirt, a spider web or an insect nest in a small filtered vent under the car, which is inexpensive to clear.
The car will drive completely normally. This matters at MOT time, because the emissions self-checks will not complete, and an incomplete monitor can fail the test on its own.
Keep the fuel filler cap properly tightened, since it is part of the sealed system being tested.
What this code means
The calibrated reference orifice used to check for fuel vapour leaks is not flowing correctly.
This is one of the more elegant pieces of engineering in emissions control, and understanding it explains the code entirely. The system has to detect a leak the size of a small pinhole in a fuel tank — and how big a leak looks depends on temperature, fuel level and altitude, none of which are constant.
So rather than measure against a fixed number, the system measures against a known hole. A precision orifice, typically half a millimetre, is built into the leak detection assembly. Before testing the tank, the module draws through that orifice and records what a leak of exactly that size looks like today — then compares the tank against it.
This code says the reference itself is unreliable. The orifice is partially blocked, so the calibration is wrong — and every leak test based on it is wrong too.
Which is why this code should be fixed before any leak code is believed. A blocked reference makes real leaks look small and small ones look large. Do not start replacing fuel tank components on the strength of a leak code stored alongside this one.
Dirt, spider webs and insect nests are the classic causes — the assembly breathes outside air, and it is usually mounted low near the tank.
Likely causes
Start here
- Blocked evaporative system filter · easy
- Blocked EVAP reference orifice · moderate
- Faulty EVAP leak detection pump · moderate
Less common
- Blocked or kinked evaporative hose · easy
- Blocked EVAP vent path · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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