What P043F means
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.
How the engine computer detects it
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.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- EVAP leak test does not run, readiness not set
- Usually no change in driving
Common causes
- Leak detection pump faulty (weak pump, leaking changeover valve, liquid damage) Most likely
- Purge valve does not seal Possible
- Pump supply or connector (contact resistance, corrosion) Possible
- Leaking hose between pump module and canister Less likely
How to diagnose P043F
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: evap leak detection pump, reference orifice, charcoal canister, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Vehicles that report P043F most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Scion XA | 2006 | 4 | 84k |
Counts of owner complaints to the NHTSA that mention P043F (9 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 4
- Auxiliary emission controls
- 3F
- Specific fault
Questions drivers ask
Can I drive with code P043F?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P043F?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P043F clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Often reported together
Codes that owners mention in the same NHTSA complaints as P043F. They can point to a shared cause, so it's worth checking them together.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.