P0496 - Evaporative Emission (EVAP) System High Purge Flow
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0496 is set when the Engine Control Module (ECM) detects an intentional or parasitic vacuum flow in the EVaporative Emission (EVAP) system when the purge solenoid should be closed. The ECM monitors this via the Fuel Tank Pressure (FTP) sensor. If a vacuum is pulled on the fuel tank while the purge valve is commanded off (0% duty cycle), it indicates a mechanical leak or a valve stuck in the open position. This leads to an over-rich condition and affects fuel trim values.
Possible Causes
Faulty EVAP Purge Solenoid (stuck open mechanically)
Short circuit to ground in the control circuit (keeping the valve energized)
Faulty Fuel Tank Pressure (FTP) sensor providing erratic voltage signals
Internal ECM fault incorrectly commanding the purge driver
Symptoms
Recommended Solution
- Visual Inspection: Check vacuum lines between the intake manifold, charcoal canister, and purge valve for cracks or loose connections.
- Component Testing: Disconnect the purge valve connector. Measure resistance across the solenoid pins; typical range is 15-30 Ohms. With power removed, try to blow through the valve. If air passes, the valve is stuck open and must be replaced.
- Circuit Testing: Check voltage at the connector. One pin should have 12V (B+) with ignition ON. The ground side managed by the ECM should not be active when commanded off.
- Advanced Diagnosis: Use a scan tool to monitor the Fuel Tank Pressure (FTP) sensor. Ensure it reports atmospheric pressure when the gas cap is off. Perform a bi-directional 'Purge/Seal' test to verify valve operation.
- Replacement: Replace the EVAP Purge Solenoid if it fails the mechanical leak test.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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