What does it mean?
P1459 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: EVAP Purge Flow Switch Circuit Malfunction .
Symptoms
- MIL on with the EVAP readiness monitor incomplete
- Switch state in live data never changes while purge is commanded
- Rough idle or a brief stumble when the purge valve opens, in some cases
- Fuel vapour smell if the canister cannot be purged
- Slight increase in fuel consumption in rare cases
Likely causes
- Purge flow switch failed or stuck in one state
- Open, shorted or high resistance wiring between the switch and the PCM
- Corroded connector at the switch, which sits in an exposed engine bay location
- Purge valve not opening, so the switch never sees flow
- Blocked or collapsed purge hose between the canister and the intake
- Saturated or blocked charcoal canister restricting vapour flow
- Vacuum leak in the purge line so the switch never reaches its threshold
How to fix it
- Watch the purge flow switch state in live data while commanding the purge valve open and closed
- Verify the purge valve itself opens and flows, since a dead valve produces the same result
- Inspect the purge hoses for collapse, cracks, blockage and disconnection
- Check the switch connector for corrosion, water and terminal pushback
- Test the switch wiring for continuity to the PCM and for shorts to ground and to power
- Apply vacuum or airflow to the switch on the bench and confirm it changes state at the expected point
- Replace the purge flow switch or the restricted canister as required, then complete an EVAP monitor drive cycle