Theory Of Operation
| EVAP SYSTEM COMPONENTS | |||
|---|---|---|---|
| CALLOUT | DESCRIPTION | CALLOUT | DESCRIPTION |
| 1 | Filter - Fresh Air Inlet | 15 | Multi-Function Control Valve (MFCV) in the Fuel Delivery Flange |
| 2 | Filter Hose (Filter to ESIM) | 16 | Fuel Tank |
| 3 | Evaporative System Integrity Monitor (ESIM) | 17 | Purge Tube (Purge Solenoid to Canister) |
| 4 | Evaporative Canister | 18 | OBD Vent Valve Tee |
| 5 | Gas Cap or Cap-less Refueling Unit (if equipped) | 19 | OBD Vent Valve |
| 6 | Recirculation Tube (metal portion) (FTPS to Fuel Filler Tube) | 20 | OBD Vent Valve Filter |
| 7 | Fuel Filler Tube | 21 | Purge Solenoid |
| 8 | Fuel Tank Pressure Sensor (FTPS) | 22 | Evaporative System Turbocharger Tee |
| 9 | Grade Vent Valve (GVV) | 23 | Check Valve (to the Turbocharger) |
| 10 | Hose - Fuel Filler Tube to ICV | 24 | Check Valve (to the Manifold) |
| 11 | Inlet Check Valve (ICV) | 25 | Ejector Tee (Venturi) |
| 12 | GVV Tube (GVV to MFCV) | 26 | Hose to the Airbox Side of the Turbocharger |
| 13 | Recirculation Tube (Fuel Tank to FTPS) | 27 | Hose to the Charge Air Cooler Side of the Turbocharger |
| 14 | Canister Tube (Fuel Tank to Canister) | 28 | Manifold Hose (Purge Solenoid to Intake Manifold) |
PURGE FLOW MONITOR: The operation of the Purge Solenoid and evaporative purge flow is monitored using inputs from the Fuel Tank Pressure Sensor . The Purge Flow Monitor will only run if the Small Leak Monitor recorded a pass on the previous ignition off event and the test data was valid. Because the leak detection diagnostics can only verify that the fuel tank side of the system is sealed while the purge valve is closed, it cannot determine if the purge line between the solenoid and Intake Manifold is pinched or leaking. The Purge Flow Monitor is needed to verify these failure modes. The Purge Flow Monitor works on the premise that as flow through the system increases, so does the pressure drop in the system. The PCM monitors the Fuel Tank Pressure Sensor and looks for increasing vacuum in the Fuel Tank with increasing purge flow. Conversely, it looks for decreasing vacuum in the Fuel Tank with decreasing flow.
- With the engine running and enable conditions met, the non-intrusive purge monitor looks for a calibrated increase in vacuum in the fuel tank with increased purge flow, referred to as side 1. If side 1 passes, the purge monitor looks for a calibrated decrease in vacuum in the Fuel Tank with decreasing purge flow, referred to as side 2. If side 2 passes, the purge monitor is complete. If the purge flow monitor fails either phase, or does not complete both phases within a specified time, an intrusive test is initiated to verify the results from the non-intrusive test.
- The intrusive diagnostic increases and decreases the purge flow in a more controlled manner to allow a more accurate test result. If the PCM detects a failure during the intrusive test, a purge system performance fault is set (P0441) .
PURGE FLOW MONITOR IN BOOST: Turbocharged engines also purge while the engine is in boost. This is achieved by having additional purge hoses and Hardware. The Boost purge monitor is used to check that this part of the Evaporative emissions system is correctly operating. The Purge flow monitor in boost is enabled to run this trip the exact same way as Purge Flow Monitor.
- The Turbo Purge Monitor will only go intrusive on this trip after a small leak passing event.
- The Monitor will only run when there is a sustained stable boost condition and not when the vehicle is at wide open throttle.
- The Monitor waits a calibrated time while stabilized boost is achieved, it then turns on the OBD Bypass Valve (#19) to relieve vacuum only. It then turns on the purge and the monitor looks for only a phase 1 decrease in vacuum in the fuel tank. If the vacuum cannot be achieved the monitor fails (P1CEA) .
Only the Fuel Tank Pressure (FTP) Sensor is used for Purge Performance diagnostics. The ESIM Switch is not used for diagnosing the purge system.