Circuit Description
The evaporative emission (EVAP) system includes the following components:
| • | The fuel tank |
| • | The EVAP vent valve |
| • | The fuel tank pressure sensor |
| • | The fuel pipes and hoses |
| • | The vapor lines |
| • | The fuel cap |
| • | The evaporative emission canister |
| • | The purge lines |
| • | The EVAP purge valve |
The EVAP purge solenoid valve allows the manifold vacuum to purge the canister. The vehicle control module (VCM) supplies a ground in order to energize the solenoid valve (purge ON). The EVAP purge solenoid control by the VCM is pulse width modulated (PWM), or turned ON and OFF several times a second. The duty cycle (pulse width) is determined by the engine operating conditions including the load, the throttle position, the coolant temperature, and the ambient temperature. The duty cycle is calculated by the VCM, and the purge valve is commanded ON when certain conditions have been met.
The system checks for conditions that cause the EVAP system to purge continuously by commanding the EVAP vent valve ON and the EVAP purge valve OFF. If the fuel tank vacuum level increases during the test, a continuous purge flow condition is indicated. The following items can cause this condition:
| • | A leaking EVAP purge valve |
| • | A grounded EVAP purge valve driver circuit |
If any of these conditions are present, DTC P1441 sets.
Conditions for Running the DTC
| • | No active manifold absolute pressure (MAP) sensor DTCs |
| • | No active throttle position (TP) sensor DTCs |
| • | No active vehicle speed sensor (VSS) DTCs |
| • | No active heated oxygen sensor (HO2S) DTCs |
| • | No active engine coolant temperature (ECT) sensor DTCs |
| • | No active intake air temperature (IAT) sensor DTCs |
| • | DTC P0125 is not active |
| • | The fuel level is more than 12.5 percent but less than 88 percent. |
| • | The system voltage is more than 10 volts but less than 17 volts. |
| • | The ECT is 4°C - 30°C (39°F - 86°F) |
| • | The IAT is 4°C - 30°C (39°F - 86°F) |
| • | The cold start ECT minus IAT is less than the following: |
| 1.5°C when the IAT is more than the ECT |
| 8°C when the ECT is more than the IAT |
| • | The barometric pressure (BARO) is more than 72.5 kPa. |
| • | The vent valve is commanded open. |
| • | The fuel tank vacuum is less than 7 inches H2O. |
| • | The throttle position is less than 75 percent. |
| • | The vehicle speed is less than 65 MPH. |
Conditions for Setting the DTC
The EVAP system develops a vacuum of more than a calibrated value when purge is not commanded
Action Taken When the DTC Sets
The VCM will turn ON the malfunction indicator lamp (MIL) after 2 consecutive driving cycles with the fault active.
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Diagnostic Aids
Important: An accurate indication of the fuel level is required for the VCM to properly Pass or Fail this DTC. Always diagnose any fuel level sensor DTCs before performing this DTCs diagnostic. Always check for fuel level sensor DTCs stored in History.
Check for the following conditions:
| • | A missing, damaged, or improperly installed fuel cap |
| • | Any missing or damaged O-rings at EVAP canister fuel vapor and purge line fittings |
| • | A cracked or punctured EVAP canister |
| • | A damaged or disconnected source vacuum line, EVAP purge line, vent hose, or fuel tank vapor line |
| • | A poor connection at the VCM: Inspect the harness connectors for the following conditions. |
| - | Any backed-out terminals |
| - | Any improper mating |
| - | Any broken locks |
| - | Any improperly formed or damaged terminals |
| - | Any poor terminal-to-wire connections |
| • | A damaged harness. Inspect the wiring harness to the EVAP vent valve, the EVAP purge valve, and the fuel tank pressure sensor for an intermittent open or short circuit. |
| • | A kinked, pinched, or plugged vacuum source, EVAP purge, or fuel tank vapor line. Verify that the lines are not restricted |
Refer to Evaporative Emission System Cleaning before starting repairs.
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
Determines if the EVAP purge valve is leaking.
-
Determines if the driver circuit for the EVAP canister purge valve is shorted to ground.
-
Determines if the driver circuit wiring for the EVAP canister purge valve or the VCM are at fault.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Does the vacuum gauge indicate any vacuum while commanded OFF? | -- | Go to Diagnostic Aids | ||
Disconnect the electrical connector from the purge valve. Does the vacuum gauge still indicate vacuum? | -- | |||
4 |
Important:: Check for carbon contamination. Refer to Evaporative Emission System Cleaning . Replace the EVAP purge valve. Is the action complete? | -- | -- | |
Does the test lamp Illuminate? | -- | |||
6 |
Important: The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
7 | Repair the short to ground in the driver circuit of the EVAP canister purge valve . Is the action complete? | -- | -- | |
8 |
Does the scan tool indicate the diagnostic Passed? | -- | -- | |
9 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to applicable DTC table | System OK |
