Evaporative Emission Leak Check Monitor

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Evaporative Emission (EVAP) Leak Check Monitor is an on-board strategy designed to detect a leak from a hole (opening) equal to or more than 0.040" (1.016 mm) in enhanced EVAP system. Proper function of individual components of enhanced EVAP system as well as its ability to flow fuel vapor to engine is also examined. EVAP leak check monitor relies on individual components of enhanced EVAP system to apply vacuum to fuel tank and then seal entire enhanced EVAP system from atmosphere. Fuel tank pressure is then monitored to determine total vacuum lost (bleed-up) for a calibrated period of time. Inputs from Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) sensor, Intake Air Temperature (IAT) sensor, Mass Air Flow (MAF) sensor, vehicle speed, Fuel Level Input (FLI) and Fuel Tank Pressure (FTP) sensor are required to enable EVAP Leak Check Monitor.

NOTE: During EVAP Leak Check Monitor Repair Verification Drive Cycle, a PCM reset will bypass the minimum soak time required to complete monitor. See OBD-II DRIVE CYCLE DESCRIPTION under DRIVE CYCLE PROCEDURE. EVAP Leak Check Monitor will not run if key is turned off after a PCM reset. EVAP Leak Check Monitor will not run if a MAF sensor failure is indicated. EVAP Leak Check Monitor will not initiate until Heated Oxygen Sensor (HO2S) Monitor has completed.

EVAP Leak Check Monitor is executed by individual components of enhanced EVAP system as follows:

EVAP canister purge valve function is to create a vacuum on fuel tank. A minimum duty cycle on EVAP canister purge valve (75 percent) must be met before EVAP Leak Check Monitor can begin.
Canister Vent (CV) solenoid will close (100 percent duty cycle) with EVAP canister purge valve at its minimum duty cycle to seal enhanced EVAP system from atmosphere and obtain a target vacuum on fuel tank.
Fuel Tank Pressure (FTP) sensor will be used by EVAP Leak Check Monitor to determine if target vacuum on fuel tank is being reached to perform leak check. Some vehicle applications with EVAP Leak Check Monitor use a remote in-line FTP sensor. Once target vacuum on fuel tank is achieved, change in fuel tank vacuum for a calibrated period of time will determine if a leak exists. If initial target vacuum cannot be reached, DTC P0455 (gross leak detected) will be set. EVAP Leak Check Monitor will abort and not continue with leak check portion of test. For some vehicle applications; if initial target vacuum cannot be reached after a refueling event and purge vapor flow is excessive, DTC P0457 (fuel cap off) is set. If initial target vacuum cannot be reached and purge flow is too small, DTC P1443 (no purge flow condition) is set. If initial target vacuum is exceeded, a system flow fault exists and DTC P1450 (unable to bleed-up fuel tank vacuum) is set. EVAP Leak Check Monitor will abort and not continue with leak check portion of test.
If target vacuum is obtained on fuel tank, change in fuel tank vacuum (bleed-up) will be calculated for a calibrated period of time. Calculated change in fuel tank vacuum will be compared to a calibrated threshold for a leak from a hole (opening) of 0.040" (1.016 mm) in enhanced EVAP system. If calculated bleed-up is less than calibrated threshold, enhanced EVAP system passes. If calibrated bleed-up exceeds calibrated threshold, test will abort and rerun test up to 3 times. If bleed-up threshold is still being exceeded after 3 tests, a vapor generation check must be performed before DTC P0442 (small leak detected) will be set. This is accomplished by returning enhanced EVAP system to atmospheric pressure by closing EVAP canister purge valve and opening CV solenoid. Once FTP sensor observes fuel tank is at atmospheric pressure, CV solenoid closes and seals enhanced EVAP system. The fuel tank pressure build-up for a calibrated period of time will be compared to a calibrated threshold for pressure build-up due to vapor generation. If fuel tank pressure build-up exceeds threshold, leak test results are invalid due to vapor generation. EVAP Leak Check Monitor will attempt to retest again. If fuel tank pressure build-up does not exceed threshold, leak test results are valid and DTC P0442 will be set.

NOTE: If the vapor generation is high on some vehicle Enhanced EVAP Systems, where the monitor does not pass, the result is treated as a no test. Thereby, the test is complete for the day.

If the 0.40" (1.016 mm) test passes, test time is extended to allow 0.020" (0.508 mm) test to run. Calculated change in fuel tank vacuum over extended time is compared to a calibrated threshold for a leak from a 0.020" (0.508 mm) hole (opening). If calculated bleed-up exceeds calibrated threshold, vapor generation is run. If vapor generation passes (no vapor generation), an internal flag is set in PCM to run a 0.020" (0.508 mm) test at idle (vehicle stopped). On the next start following a long engine off period, enhanced EVAP system will be sealed and evacuated for first 10 minutes of operation. If appropriate conditions are met, a 0.020" (0.508 mm) leak check is conducted at idle. If test at idles fails, a DTC P0456 will be set. There is no vapor generation test with idle test.
Malfunction Indicator Lamp (MIL) is activated for DTCs P0442, P0455, P0456, P0457, P1443 and P1450 (or P446) after two occurrences of the same fault. The MIL can also be activated for any Enhanced EVAP system component DTCs in the same manner. The Enhanced EVAP system component DTCs P0443, P0452, P0453 and P1451 are tested as part of Comprehensive Component Monitor (CCM). For additional information, see COMPREHENSIVE COMPONENT MONITOR .