EVAP Running Loss System Monitor Procedure

This is an on-board strategy designed to detect a leak from a hole (opening) equal to or greater than 1.016 mm (0.040") in the EVAP system. The proper function of the individual components of the EVAP system as well as its ability to flow fuel vapor to the engine is also examined.

The EVAP Running Loss System Monitor relies on the individual components of the EVAP system to apply vacuum to the fuel tank and then seal the system. The fuel tank pressure is then monitored to determine the total vacuum lost (bleed-up) for a calibrated period of time. Inputs from the Engine Coolant Temperature (ECT) sensor or Cylinder Head Temperature (CHT) sensor, Intake Air Temperature (IAT) sensor, Mass Air Flow (MAF) sensor, Vehicle Speed Sensor (VSS) or Output Shaft Sensor (055), Fuel Level Input (FLI) sensor, and Fuel Tank Pressure (FTP) sensor are required to enable the EVAP Running Loss System Monitor. The Powertrain Control Module (PCM) monitors the time since power down and will not allow the EVAP Running Loss System Monitor to run until the minimum soak timer (6-10 hours) has expired.

NOTE
DURING THE EVAP RUNNING LOSS SYSTEM MONITOR DRIVE CYCLE, A PCM RESET (CLEARING CONTINUOUS CODES) WITH KEY ON, ENGINE OFF (KOEO) WILL BYPASS THE MINIMUM SOAK TIME REQUIRED TO COMPLETE THE MONITOR. THE EVAP RUNNING LOSS SYSTEM MONITOR WILL NOT RUN IF THE KEY IS TURNED OFF AFTER A PCM RESET UNLESS THE MINIMUM SOAK TIME WAS REACHED. THE EVAP RUNNING LOSS SYSTEM MONITOR WILL NOT RUN IF A MAF, ECT, IAT, VSS, FLI, OR FTP SENSOR FAILURE(S) IS INDICATED. THE EVAP RUNNING LOSS SYSTEM MONITOR WILL NOT INITIATE UNTIL THE HEATED OXYGEN SENSOR (H025) MONITOR HAS COMPLETED.

The EVAP Running Loss System Monitor is executed by the individual components of the EVAP Running Loss System as follows:

1. The EVAP canister purge valve applies a vacuum to the fuel tank. A minimum duty cycle on the EVAP canister purge valve (75%) must be met before the EVAP Running Loss System Monitor can begin.

2. The Canister Vent (CV) solenoid will close (100% duty cycle) to seal the EVAP system.

3. The FTP sensor will be used by the EVAP Running Loss System Monitor to determine if the target vacuum on the fuel tank is being reached to perform the leak check.

4. If the initial target vacuum cannot be reached, DTC P0455 (large leak detected) will be set. The EVAP Running Loss System Monitor will abort and not continue with the leak check portion of the test.

Once the target vacuum is obtained on the fuel tank, the EVAP canister purge valve closes and the change in the fuel tank vacuum will be monitored over a calibrated period of time. If the change in fuel tank vacuum is less than the calibrated threshold, the EVAP Running Loss System Monitor passes.

If the change in fuel tank vacuum exceeds the calibrated threshold, the test will rerun up to three (3) times. If the calibrated threshold is still being exceeded after three tests, a vapor generation check must be performed before DTC P0442 (small leak detected) will be set. The system accomplishes this by returning the EVAP system to atmospheric pressure by closing the EVAP canister purge valve and opening the CV solenoid.

Once the FTP sensor observes the fuel tank is at atmospheric pressure (approximately 2.6 volts), the CV solenoid closes (seals the EVAP system). If the fuel tank pressure buildup exceeds the calibrated threshold, the leak test results are invalidated due to excessive vapor (the EVAP Running Loss System Monitor will pass and complete). If the fuel tank pressure buildup does not exceed the calibrated threshold, the leak test results are valid and DTC P0442 will be set.

5. The MIL is activated for DTCs P0442 and P0455 after two (2) occurrences of the same fault.

NOTE
REFER TO THE LATEST POWERTRAIN CONTROL/EMISSIONS DIAGNOSIS (PC/ED) SERVICE MANUAL ON SBDS OR SERVICE BAY TECHNICAL SYSTEM (SBTS) FOR INFORMATION ON DTCs P0443, P0446, P0452, P0453, P1450, AND P1451.