GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2008 🢒 LaCrosse 🢒 DTC 🢒 DTC P0496

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    •  Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0496 : Evaporative Emissions (EVAP) System Continuous Purge Flow

Circuit Description

This DTC tests for continuous intake manifold vacuum flow to the Evaporative Emission (EVAP) System. The control module seals the EVAP system by commanding the EVAP canister purge solenoid valve Closed and the EVAP canister vent solenoid valve Closed. The control module monitors the fuel tank pressure (FTP) sensor to determine if a vacuum is being drawn on the EVAP system. If vacuum in the EVAP system is greater than a predetermined value within a predetermined time, this DTC sets.

FTP Sensor Signal Voltage

Fuel Tank Pressure

High, Approximately 1.5 Volts or greater

Negative Pressure/Vacuum

Low, Approximately 1.5 Volts or Less

Positive Pressure

Conditions for Running the DTC
    • Before the engine control module (ECM) can report DTC P0496 failed, DTCs P0451, P0452, and P0453 must run and pass.
    • DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0221, P0222, P0223, P0443, P0446, P0449, P0458, P0459, P0496, P0498, P0499, P0506, P0507, P0560, P0562, P0563, P0700, P2122, P2123, P2127, P2128, and P2138 are not set.
    • The ignition 1 voltage is between 11-18 volts.
    • The fuel system is operating in closed loop.
    • The engine is idling.
    • The ambient air temperature is between 2-32°C (36-90°F).
    • The start-up engine coolant temperature (ECT) is within 10°C (18°F) of ambient air temperature.
    • The FTP is between -18.7 to +7.5 mm Hg (-10.0 to +4.0 in H2O).
    • The volumetric efficiency is less than 35 percent.
    • The barometric pressure (BARO) is greater than 68 kPa.
    • The fuel level is between 12-88 percent.
    • The vehicle speed sensor (VSS) is less than 2 km/h (3 mph).
    • The engine is operating for greater than 16 minutes or the long term fuel is stable.
    • DTC P0496 will attempt to run up to 10 times or the test completes successfully once per ignition cycle.

Conditions for Setting the DTC
    • The control module detects vacuum during a non-purge condition.
    • The condition exists for greater than 4 seconds or for a cumulative of 50 seconds.

Action Taken When the DTC Sets

DTC P0496 is a Type A/B DTC.

Conditions for Clearing the DTC

DTC P0496 is a Type A/B DTC.

Diagnostic Aids
    • Observe the Freeze Frame/Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition occurs that caused the DTC to set . This may assist in diagnosing the condition.
    • The EVAP system tests run when engine is first started and meets The Conditions for Running the DTC. An intermittent condition could be caused by an improperly installed or damaged EVAP canister purge solenoid valve , or by a temporary blockage or restriction in the EVAP canister purge solenoid valve.

Reference Information

Schematic Reference

Engine Controls Schematics

Description and Operation

Evaporative Emission Control System Description

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the EVAP purge solenoid valve.
  2. Engine idling, command the EVAP vent closed with a scan tool.
  3. Increase the engine speed to 1,200-1,500 RPM.
  4. Observe the scan tool FTP sensor inches H2O. Verify the scan tool FTP sensor H2O parameter is -0.5 to +0.5 inches H2O.
    5. ⇒If greater than the specified range, replace the EVAP purge solenoid valve.
  5. Ignition OFF, disconnect the EVAP purge solenoid valve pipe.
  6. Ignition ON, observe the scan tool FTP sensor inches H2O parameter.
  7. Verify the FTP sensor is -0.5 to +0.5 inches H2O.
    8. ⇒If greater than the specified range, replace the FTP sensor.

Repair Instructions
    •  Evaporative Emission Canister Purge Solenoid Valve Replacement
    •  Fuel Tank Pressure Sensor Replacement
    •  Control Module References for engine control module replacement, setup, and programming

Repair Verification
  1. Engine idling, command the EVAP vent solenoid closed with a scan tool.
  2. Increase the engine speed to 1,200-1,500 RPM.
  3. Observe the FTP sensor in H2O parameter with a scan tool. Verify the FTP sensor parameter is -0.5 to +0.5 inches H2O.
  4. Clear the DTCs with a scan tool.