Circuit Description
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 ECM monitors the EVAP system for circuit faults in the fuel tank
pressure sensor, EVAP purge solenoid and EVAP vent solenoid circuits. The ECM also
monitors the EVAP system for small and large leaks. During DTC P0440 diagnostic, the
EVAP purge solenoid is commanded to a fixed duty cycle (pulses valve) and the EVAP
vent solenoid is commanded On (closed) in order to build vacuum. Once vacuum is obtained,
the EVAP vent solenoid is commanded Off and the vacuum should decrease rapidly. DTC
P0440 sets when the fuel tank pressure sensor indicates less than atmospheric pressure
after a certain length of time (vent system is either blocked or closed).
DTC Parameters
DTC P0440 sets when the fuel tank pressure sensor indicates less than 2.0 volts
(vent system is either blocked or closed) during the diagnostic system test when:
| • | Engine load less than 35 %. |
| • | MAP is greater than 40 kPa. |
| • | Battery voltage is greater than 11.0 volts. |
| • | ECT at engine startup is between 8°C and 75°C (46° and 167°F). |
| • | IAT is between 8°C and 50°C (46° and 122°F). |
| • | Long term fuel cells not cleared (if cleared, engine must run longer than
16 minutes and 45). |
| • | Fuel level between 1.3 and 12.7 gallons (5-48 liters). |
| • | Altitude less than 9842 ft. |
| • | No battery voltage, ECM internal fault, ECT, EGR, EVAP purge control,
EVAP vent control, fuel tank pressure, HO2S, IAC, MAP, misfire, TP or VSS DTCs have
been set. |
DTC P0440 diagnostic is run once (usually for 40 seconds if no faults
exist) during the EVAP diagnostic test once the above conditions have been met.
If the ECM cannot run this test during the ignition cycle, it will monitor the
fuel tank pressure sensor a maximum of two times for 15 seconds and set this DTC if
the reading is less than 2.0 volts (11.25 mmHg lower than atmospheric pressure).
P0440 is a (type B) DTC.
Diagnostic Aids
Important: The ECM uses the fuel tank pressure sensor
to detect the vacuum decay of the EVAP vent solenoid diagnostic. Make sure the fuel
pressure sensor is not skewed by verifying FUEL TANK PRESS. SENSOR on Scan tool is
between 2.35 and 2.85 volts with ignition On and fuel cap removed.
Check the following for causes of a blocked vent system:
| • | EVAP vent solenoid blocked or stuck valve. |
| • | Vent hose plugged, kinked or pinched. |
| • | EVAP canister restricted. |
