What it means
Same as P04AB with the control line shorted to ground. The evaporative system captures fuel vapor from the tank and purges it into intake; leaks or stuck purge valves leak hydrocarbons and cause emissions failures.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
EVAP purge control valve B is a solenoid that meters fuel vapor from the canister into the engine intake. P04AC sets when the module detects voltage on valve B's control circuit lower than expected, commonly because the control wire is shorted to ground or the circuit has a poor connection.
Common causes
Most likely first.
- Control line shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light on
- Possible smell of fuel near tank or engine bay
- Failed emissions inspection
- Loose-cap warning may appear
How to diagnose it
- Review freeze-frame and EVAP live data to confirm the fault is on purge valve B and note whether it appears when the valve is commanded.
- Inspect valve B's connector and harness for chafing through insulation, wet or corroded pins, and terminals that are loose or pushed back.
- Check whether the control wire is shorted to ground, isolating the valve and module as directed by the service information.
- Check connector terminal condition and circuit continuity to locate excessive resistance or a ground short in the valve B control path.
- Test valve B's solenoid and the module-side control circuit against the manufacturer's specification before replacing parts.
Common fixes
- Repair the valve B control wire where it has rubbed through and contacted ground.
- Clean or replace corroded terminals and restore a secure connector fit.
- Repair damaged harness insulation and secure the wiring away from rubbing points.
- Replace purge valve B if testing shows an internal electrical fault.
Can I keep driving?
You can generally drive gently if the engine runs normally, but address the fault soon and avoid disregarding a fuel-vapor smell. Poor purge control can increase emissions and cause an inspection failure.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.