P04AE code meaning
EVAP System Purge Control Valve B Performance/Stuck Open
Powertrain system Generic code P04xx codes Check engine light
What P04AE 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. Purge valve B is a second electric purge valve, usually for the high-load purge line of a turbo engine, which purges to the compressor inlet when there is boost in the manifold (Ford patent). Many makers solve this path with one purge valve and passive check valves instead – Ford tests it as P04F0 – and then have no valve B. CARB requires every purge path to be checked. P04AE is the function check of purge valve B: flow, tank pressure or mixture react although the valve is commanded closed. It is documented on Subaru's FA24 turbo engines (Legacy/Outback 2.4, WRX, Ascent) as a known false trigger, fixed by an engine module software update – the bulletin advises checking the software before replacing the valve. Subaru publishes no thresholds.
P04AE at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 1.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P04AE
- Check engine light on
- Rough idle or starting problems after refuelling
- Often no change in driving (software false trigger)
Common causes of P04AE
- Most likelyEngine module software (Subaru FA24: known false trigger)
- PossiblePurge valve B leaking or stuck open (charcoal dust, wear)
- Less likelyPurge lines swapped after a repair
- Less likelyTank pressure sensor misreading
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
EVAP purge valve bHigh load purge linePurge valve wiringEngine control module
What each part of P04AE means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| AE | The exact fault in that area. |
What to do next
- Note P04AE and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P04AE
What does P04AE mean?
P04AE means "EVAP System Purge Control Valve B Performance/Stuck Open". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P04AE?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P04AE fail an emissions test?
Yes, it can. P04AE is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P04AE to fix?
Difficulty: medium. A typical repair takes 0.5 to 1.5 hours of work. This is a job for a workshop.
Will P04AE clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.