P04AD

What it means

P04AD means the engine control unit has detected a high voltage or signal condition in the control circuit of EVAP purge control valve B, a second purge valve on vehicles that have one. The control unit monitors the circuit when it commands the valve and sets the code when the voltage is higher than expected. Causes include a short to voltage, an open circuit or a fault inside the valve or control unit, depending on how the circuit is designed.

Symptoms

• Engine warning light on
• Rough idle or occasional stalling after refuelling
• Difficulty starting after refuelling
• Slight hesitation or uneven running when the purge valve should be operating
• Fuel smell near the engine bay or fuel filler
• Failed emissions test or evaporative system monitor not completing

Possible causes

• Faulty purge control valve B (internal coil fault or valve stuck)likely
• Damaged, chafed or corroded wiring to the valve, including a short to a power supply or an open circuitlikely
• Poor connection at the valve connector or control unit plug (bent, pushed-back or corroded terminals)likely
• Water ingress or heat damage in the connector or harness near the valvepossible
• Blown fuse or fault in the valve's power supply feed, depending on the circuit designpossible
• Fault in the engine control unit output driverrare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data. Look for other EVAP or purge valve codes that point to a shared fault.
2. Visually inspect the purge valve B, its hoses and its connector for damage, looseness, contamination or water ingress. Its location depends on the model and engine.
3. Inspect the wiring between the valve and the control unit for chafing, melted insulation or rodent damage, and check the terminals for corrosion or push-back.
4. Check the valve's power supply and fuse using the manufacturer's wiring diagram, as the circuit design varies between models.
5. Measure the valve coil resistance and compare it with the specification for that vehicle.
6. With the valve connected and the ignition on, use a scan tool bidirectional test to command the valve and check for a click and a change in the live data. Back-probe the control circuit with a multimeter or scope to see the voltage change.
7. Test the control wire for a short to voltage or an open circuit with the connector unplugged at both ends, following the wiring diagram.
8. Clear the code and road test. If it returns straight away with a known good valve and wiring, investigate the control unit driver and check for any applicable software updates.

How to fix

• Replace purge control valve B if its resistance or operation is out of specification.
• Repair or replace damaged wiring and fix any short to voltage or open circuit.
• Clean, repair or replace corroded or damaged connector terminals and reseat the connectors securely.
• Restore the power supply by replacing a blown fuse once the cause of the overload is found, or by repairing the supply wiring.
• Repair or replace the control unit only after the wiring and valve have been proved good, and apply any manufacturer calibration update if one is known to address the fault.

Can I keep driving?

Nearby codes

• P04ACGenericEVAP System Purge Control Valve B Circuit Low
• P04AEGenericEVAP System Purge Control Valve B Performance/Stuck Open