OBD-II code · Powertrain (generic)
P04AC EVAP System Purge Control Valve B Circuit Low
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.
Is it safe to drive with P04AC?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyControl line shorted to ground
- Less likelyConnector pins corroded - high contact resistance
- Less likelyHarness 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
Repair at a glance
- Difficulty
- Easy
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.5–1.4 h
- Emissions test
- Likely to fail
- Parts involved
- Evap Purge Valve B
Related codes
- P0458EVAP System Purge Control Valve A Circuit Low
- P04A9Exhaust Pressure Control Valve B Position Sensor Circuit High
- P04AAExhaust Pressure Control Valve B Position Sensor Circuit Intermittent or Erratic
- P04ABEVAP System Purge Control Valve B Circuit Open
- P04ADEVAP System Purge Control Valve B Circuit High
- P04AEEVAP System Purge Control Valve B Performance Stuck Open
- P04AFEVAP System Purge Control Valve B Stuck Closed
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.