P0496

DTC P0496: Evaporative Emission System Continuous Purge Flow

System Description
The evaporative (EVAP) emission system includes the following components:
- Fuel tank
- EVAP emission vent solenoid
- Fuel tank pressure sensor
- Fuel pipes and hoses
- Fuel vapor lines
- Fuel cap
- EVAP emission canister
- Purge lines
- EVAP emission canister purge valve
- EVAP emission service port

The EVAP emission system is checked by applying vacuum to the EVAP emission system and monitoring for a vacuum decay. The engine control module (ECM) monitors the vacuum level through the fuel tank pressure sensor signal.
At the appropriate time, the EVAP emission canister purge valve and the EVAP emission vent solenoid are turned ON, allowing the engine to draw a small vacuum on the entire EVAP emission system. After the desired vacuum level has been achieved, the EVAP emission canister purge valve is turned OFF, sealing the system. The EVAP emission canister purge valve allows manifold vacuum to purge the canister. The ECM supplies a ground to energize the solenoid valve (purge ON). The EVAP emission canister purge valve control is Pulse Width Modulated (PWM) or turned ON and OFF several times a second. The duty cycle (pulse width) is determined by engine operating conditions including load, Throttle Position (TP), Engine Coolant Temperature (ECT) and ambient temperature. The duty cycle is calculated by the ECM and the output is commanded when the appropriate conditions have been met.
The system checks for conditions that cause the EVAP emission system to purge continuously by commanding the EVAP emission vent solenoid ON and the EVAP emission canister purge valve OFF (EVAP emission vent solenoid CLOSED, EVAP emission purge PWM 0%).
If the fuel tank vacuum level increases during the test, a continuous purge flow condition is indicated. This can be caused by the following conditions:
- EVAP emission canister purge valve leaking.
- EVAP emission purge and engine vacuum lines switched at the EVAP emission canister purge valve.
- EVAP emission canister purge valve driver circuit grounded.

If any of these conditions are present, DTC P0496 will set.

Conditions for Setting the DTC
- DTC(s) P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0201, P0202, P0203, P0204, P0300, P0402, P0404, P0405, P0406, P0443, P0452, P0453, P0488, P0502, P0462, P0463, P0506, P0507, P2195, and P2196 will not set.

Common EVPD Enable Criteria
- System voltage is between 11V and 16V.
- Barometric Pressure (BARO) is greater than 72.3 kPa (10.5 psi).
- Engine soak time is greater than 720 minutes. Or, at startup IAT-ECT is less than 8�C (46.4�F).
- At start up, Engine coolant temperature (ECT) and Intake Air Temperature (IAT) are between 4�C (39.2�F) and 34�C (93.2�F).
- Startup IAT-IAT is less than 3�C (5.4�F).
- Purge enable time is less than pre-determined value based on startup ECT.
- Fuel level is between 6% and 93%.
- Engine run time is between 1 second and 360 seconds plus purge enable time.

Continuous Purge Flow Enable Criteria
- Engine run time is between 1 second and 100 seconds.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- The MIL will turn off after three consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.

Diagnostic Aids
Although this DTC is considered a type A diagnostic (refer to "Engine Control Module"), it acts like a type B diagnostic under certain conditions. Whenever this diagnostic reports the system has passed, or if the battery is disconnected, the diagnostic must fail twice before setting a DTC. The initial failure is not reported to the diagnostic executive or displayed on a scan tool. A passing system always reports to the diagnostic executive immediately. Check for the following conditions:
Poor connection at ECM. Inspect harness connectors for the following conditions:
1) Poor connection at ECM. Inspect harness connectors for the following conditions:
- Backed-out terminals
- Improper mating
- Broken locks
- Improperly formed
- Damaged terminals
- Poor terminal-to-wire connection

2) Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, connect the EVAP emission pressure/purge cart to the EVAP emission service port, pressurize the EVAP emission system to 10 inches O2S2 and observe the Fuel Tank Vacuum Pressure display on the scan tool while moving connectors and wiring harnesses related to the EVAP emission canister purge valve. A sudden change in the display will indicate the location of the fault.

3) Incorrect vacuum line routing. Verify that the source vacuum line routing to the EVAP emission canister purge valve is correct and that the EVAP emission purge and source vacuum lines to the EVAP emission canister purge valve are not switched.

4) Loose Carbon in the purge solenoid. Blow out the lines and replace the purge canister.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
(1) The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
(3) If an EVAP canister purge valve electrical malfunction is present, the purge system will not operate correctly. Repairing the electrical malfunction will very likely correct the condition that set DTC P0496.
(4) Checks the fuel tank pressure sensor at ambient pressure.
(6) Verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes.
(7) If the EVAP purge and engine vacuum lines are switched at the EVAP canister purge valve, the solenoid valve will leak vacuum.
(11) Duplicates the On-Board diagnostic test.

Steps 1-6:

Steps 7-11:

Troubleshooting