P0459: EVAP System Purge Control Valve A Circuit High
Standardized SAE J2012 code · P04xx — Auxiliary emission controls
What does P0459 mean?
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 A is switched to ground by the module and fed from the main relay. P0459 means its control wire is shorted to positive, detected with the driver switched on, when the line should sit at ground (GM 20 of 25 samples, MIL after two trips; Saab ME9 above 4.6 V). The valve then cannot open, the canister is not purged and fills up; the driver protects itself and the leak tests are suspended.
The code tells you which monitor failed, not which part is broken. Test before replacing parts.
Symptoms
- Check engine light on
- Fuel smell when the canister is full
- EVAP readiness not set
Common causes
- High Control wire shorted to battery voltage or supply
- Medium Purge valve coil low-resistance (shorted turns)
- Medium Connector or harness damaged
- Low Engine module
Likelihood is a general estimate across vehicles; your make and model may differ.
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