P043F: EVAP System Leak Detection Reference Orifice High Flow

The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. Systems with a leak detection pump (Bosch DM-TL at VW, Audi, BMW and Maserati, Denso's canister pump module at Toyota/Lexus) first measure a reference value with the pump working only through a built-in 0.5 mm (0.020 in) orifice; it is the yardstick for the small-leak test that CARB requires. P043F means the reference measurement shows too much flow – the reference vacuum or pressure does not reach the expected value, because the reference path or changeover valve leaks, the pump is weak, or air enters through leaking valves in the test path. The leak test can then not be judged, since a weak yardstick would hide leaks. GM and Ford do not use the code.

Symptoms

• Check engine light on
• EVAP leak test does not run, readiness not set
• Usually no change in driving

Most likely causes

• Leak detection pump faulty (weak pump, leaking changeover valve, liquid damage)
• Purge valve does not seal
• Pump supply or connector (contact resistance, corrosion)
• Leaking hose between pump module and canister

What to check, in order

Start with the simplest. You can tick off each step.

1. Start with the fuel cap: tighten it fully and check its seal
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Inspect the hoses and connections around the tank and the charcoal canister
4. Use the scanner to test the purge and vent solenoid valves
5. Run a smoke test to find small leaks

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P043F means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 4: Emissions
• 3F: Specific fault in that system

Frequently asked questions

Can I keep driving with code P043F?

Yes, you can normally keep driving. If there is a strong smell of gasoline, find the leak before continuing and do not smoke nearby.

What causes code P043F?

The most common causes are: leak detection pump faulty (weak pump, leaking changeover valve, liquid damage); purge valve does not seal; pump supply or connector (contact resistance, corrosion).

Related codes

• P043EEVAP System Leak Detection Reference Orifice Low Flow
• P2401EVAP System Leak Detection Pump Control Circuit Low
• P2402EVAP System Leak Detection Pump Control Circuit High
• P2419EVAP System Switching Valve Control Circuit Low
• P0456EVAP System Leak Detected (very small leak)

Sources

• static.nhtsa.gov: SB 10053936 1988
• patents.google.com: US6964193
• patents.google.com: US9109548
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.