P04AE

What it means

P04AE means the engine control unit has decided that purge control valve B in the evaporative emissions (EVAP) system is not closing properly, so it is stuck open or leaking when it should be shut. The unit usually sets it when it sees unexpected vapour flow, a change in fuel trim or a pressure or vacuum change while the valve is commanded closed. Which valve is 'B', and how it is plumbed, depends on the model and engine, so check manufacturer data.

Symptoms

• Malfunction indicator lamp on
• Rough idle or stalling, especially just after refuelling
• Hard starting or long cranking after filling the tank
• Fuel trims out of range, usually rich at idle
• Fuel smell around the engine bay
• Other EVAP codes stored alongside it

Possible causes

• Purge valve B held open by dirt, debris or a worn seatlikely
• Purge valve B internally leaking or failed mechanicallylikely
• Electrical fault in the valve circuit such as a short to supply, a damaged wire or a corroded connector holding the valve openpossible
• Charcoal canister saturated with fuel or contaminated, often from overfilling the tankpossible
• Cracked, disconnected or wrongly routed vacuum or vapour hoses, or a faulty check valve (on systems with two purge paths)possible
• Fault in the control unit's valve driver circuitrare

How to diagnose

1. Read the stored codes and freeze frame data, noting fuel level, engine load, temperature and whether the fault happened at idle or after a start
2. Check for other EVAP, fuel trim or misfire codes and look for any relevant technical service bulletins for the model
3. Inspect the valve, its hoses and its connector for damage, wrong routing, corrosion and loose fittings
4. Check that the valve is actually valve B for the engine and find its wiring diagram and test values in manufacturer data
5. With the valve disconnected and unpowered, apply a small vacuum to the valve and confirm it holds; if it leaks, it is stuck open
6. Use a scan tool to command the valve on and off, listening for a click and watching fuel trims, manifold pressure and idle quality for changes
7. Measure the valve resistance and check for supply, ground and the control signal at the connector against specification
8. Inspect the canister and vapour lines for liquid fuel or blockage, and smoke test the EVAP system for leaks

How to fix

• Replace purge valve B if it fails to hold vacuum or does not operate correctly
• Repair or replace damaged wiring, terminals or the connector in the valve circuit
• Replace the charcoal canister if it is contaminated with fuel or damaged, and correct the cause such as overfilling
• Replace cracked, loose or wrongly routed hoses and any faulty check valve
• Clear the code after repair and road test, then confirm fuel trims are normal and the code does not return

Can I keep driving?

Nearby codes

• P04ADGenericEVAP System Purge Control Valve B Circuit High
• P04AFGenericEVAP System Purge Control Valve B Stuck Closed