Powertrain Diagnosis

EVAP System Test:

The Evaporative Emission (EVAP) system is used to store fuel vapors as to reduce the amount of unburned fuel from escaping into the atmosphere. The EVAP system consists of the EVAP canister, fuel tank pressure sensor, EVAP lines and hoses, EVAP purge solenoid (normally closed), EVAP service port, EVAP vent solenoid (normally open) and fuel tank. The PCM monitors the EVAP system for circuit faults in the fuel tank pressure sensor, EVAP purge solenoid and EVAP vent solenoid circuits. The PCM also monitors the EVAP system for small and large leaks. During the DTC P0440 diagnostic, the PCM monitors the fuel tank pressure sensor for an atmospheric pressure reading when all of the DTC parameters have been met with engine running. The PCM will then command the EVAP vent solenoid On (close valve) and command the EVAP purge solenoid On (open valve). The PCM will let the pressure drop in the fuel tank for a certain length of time after which it will turn Off the EVAP purge solenoid. DTC P0440 sets when a certain vacuum in the fuel tank could not be achieved due to a large leak.

DTC PARAMETERS
DTC P0440 will set if 8 inches of H2O cannot be pulled on the EVAP system indicating a large EVAP leak when:
^ EVAP vent solenoid is commanded On (closed)
^ EVAP purge solenoid is commanded On (open)
^ Engine run time is greater than 2 seconds
^ Fuel tank level is between 15 and 85% full
^ Baro is greater than 81 kPa
^ IAT at engine start-up is between 5° and 32°C (41° and 90°F)
^ ECT and IAT are within 10°C (50°F) of each other
^ No ECT, fuel tank pressure, IAT, MAP or VSS DTCs have been set

DTC P0440 diagnostic runs once per ignition cycle once the above conditions have been met. If this test fails, a warm test will be performed and can only PASS a diagnostic test, not fail it. The purpose of this test is keep the MIL Off during the initial test if the customer starts the vehicle with the fuel cap off.

DTC P0440 is a type A DTC.


DIAGNOSTIC AIDS

IMPORTANT:
^ If DTC P0444, P0445, P0447, P0448 or P1441 is set, diagnose that DTC first as they are most likely the cause of this DTC. A diagnosed EVAP purge solenoid or EVAP vent solenoid circuit fault may have caused this DTC to set.
^ The PCM uses the fuel tank pressure sensor to detect the amount of vacuum pulled on the EVAP system during the large leak diagnostic. Make sure the fuel pressure sensor is not skewed by verifying FUEL TANK PRESSURE on Scan tool is between 1.3 and 1.7 volts with ignition On and fuel cap removed.

Make a visual inspection for a large leak of the EVAP system. Using Scan tool, perform the EVAP SERVICE BAY TEST which will verify that a large leak is present. Use the EVAP Pressure/Purge Diagnostic Chart and Ultrasonic leak detector to locate the large leak.

Possible causes of a large leak:
^ Fuel cap missing, incorrectly installed or leaking
^ EVAP vent solenoid stuck open
^ EVAP purge solenoid stuck closed or blocked
^ EVAP vent hose loose or damaged
^ EVAP canister leaking
^ Fuel sender assembly 0-ring leaking
^ Fuel tank or filler neck leaking

NOTE: A very large leak such as a missing fuel cap may be difficult to pickup with the ultrasonic leak detector.