Circuit Description
The evaporative system (EVAP) includes the following components:
| • | The fuel tank |
| • | The EVAP vent solenoid |
| • | The fuel tank pressure sensor |
| • | The fuel pipes and the hoses |
| • | The fuel vapor lines |
| • | The fuel cap |
| • | The EVAP canister |
| • | The purge lines |
| • | The EVAP canister purge solenoid valve |
| • | The EVAP service port |
The EVAP system is checked by applying vacuum to the EVAP system and by monitoring for a vacuum decay. The Powertrain Control Module (PCM) monitors the vacuum level through the fuel tank pressure sensor signal. At an appropriate time, the EVAP canister purge solenoid valve and the EVAP vent solenoid are turned ON, allowing the engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP canister purge solenoid valve is turned OFF, sealing the system.
The EVAP canister purge solenoid valve controls the amount of engine vacuum applied to the EVAP canister. The PCM supplies a ground in order to purge ON, the solenoid valve. The EVAP canister purge solenoid valve control is pulse width modulated (PWM) from 8 to 16 cycles per second. The duty cycle, or pulse width, is determined by the engine operating conditions, including the following items:
| • | The engine load |
| • | The throttle position |
| • | The engine coolant temperature |
| • | The ambient temperature |
The system checks for conditions that cause the EVAP system to purge continuously by commanding the EVAP canister purge solenoid valve OFF. If the fuel tank vacuum level increases during the test, a continuous purge flow condition is indicated. This can be caused by the following conditions:
| • | A leak in the EVAP canister purge solenoid valve. |
| • | The following lines may be switched at the EVAP canister purge solenoid valve: |
| - | The EVAP purge |
| - | The engine vacuum |
| • | The EVAP canister purge solenoid valve driver circuit is grounded. |
If any of these conditions are present, DTC P1441 will set.
Conditions for Running the DTC
| • | No active MAP DTC's |
| • | No active IAT DTC's |
| • | No active ECT DTC's |
| • | No active TP DTC's |
| • | No active Oxygen Sensor DTC's |
| • | No active Fuel Tank Pressure DTC's |
| • | No active VSS DTC's |
| • | No active PCM Memory DTC's |
| • | The BARO is more than 75 kPa. |
| • | The Start-Up ECT and IAT are between 4° C and 30° C (39°F and 86°F) |
| • | The Start-Up ECT is not more than 8° C (14°F) above Start-Up IAT. |
| • | The Start-Up IAT is not more than 1.5° C (3°F) above Start-Up ECT. |
| • | The fuel tank level is between 15 percent and 85 percent. |
| • | The TP sensor is between 7 percent and 35 percent. |
| • | The Vehicle Speed is less than 70° MPH (113 KPH). |
| • | The engine is running. |
Conditions for Setting the DTC
The EVAP system is unable to detect vacuum during the diagnostic test.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information. |
| • | The EVAP purge function is disabled until the diagnostic passes. |
| • | A history DTC stores. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs a pass. |
| • | A history DTC will clear after 40 consecutive warm up cycles without a malfunction. |
| • | A scan tool can clear the DTCs. |
Diagnostic Aids
Although this DTC is considered a type A diagnostic, the DTC acts like a type B diagnostic under certain conditions. Whenever this diagnostic reports the system has passed, or if the battery is disconnected, the diagnostic must fail twice before setting a DTC. The initial failure is not reported to the diagnostic executive or displayed on a scan tool. A passing system always reports to the diagnostic executive immediately.
Check for the following conditions:
| • | A poor connection at the PCM: Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | A damaged harness: Inspect the wiring harness for damage. If the harness appears to be OK, connect the EVAP pressure/purge cart to the EVAP service port, pressurize the EVAP system to 10 in. H2O and observe the Fuel Tank Vacuum Pressure display on the scan tool while moving the connectors and the wiring harnesses related to the EVAP canister purge valve. A sudden change in the display will indicate the location of the fault. |
| • | An incorrect vacuum line routing: Verify that the source vacuum line routing to the EVAP canister purge valve is correct and that the EVAP purge and source vacuum lines to the EVAP canister purge valve are not switched. |
Check for charcoal particles. Refer to Evaporative Emission System Cleaning before starting repairs.
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
-
The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data captured when this DTC sets. The scan tool stores this data for later reference.
-
If an EVAP canister purge valve electrical malfunction is present, the purge system will not operate correctly. Repairing the electrical malfunction will very likely correct the condition that set DTC P1441.
-
This step checks the fuel tank pressure sensor at the ambient pressure.
-
This step verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes.
-
If the EVAP purge and engine vacuum lines are switched at the EVAP canister purge valve, the solenoid valve will leak vacuum.
-
This step duplicates the Powertrain On-Board Diagnostic test.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
2 |
Are any DTCs set? | -- | Go to the applicable DTC table | |
Does the purge valve and vent solenoid click when command ON and OFF? | -- | |||
Is the fuel tank pressure at the specified value? | 0 mmHg (±2.4 mmHg) | Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage or | ||
5 |
Important:: Before continuing with the diagnosis, zero the EVAP Pressure and Vacuum gauges on the EVAP pressure/purge cart J 41413 . Also read the temperature variation. Refer to tool operating instructions.
Important: Do not exceed the pressure in the specified value. Can the specified value be achieved? | 5 in H2O | ||
Is the fuel tank pressure at the specified value? | 12 mmHg (±4.8 mmHg) | Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage or | ||
7 |
Does the EVAP canister purge valve achieve and maintain vacuum at the specified value? | 15 in. Hg | ||
Check the EVAP purge and source vacuum line routing and connections at the EVAP canister purge valve. Are the EVAP purge and source vacuum lines connected correctly at the EVAP canister purge valve? | -- | Go to Diagnostic Aids | ||
9 | Replace the EVAP canister purge valve. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement . Is the action complete? | -- | -- | |
10 | Correct the EVAP purge and source vacuum line routing and connections. Is the action complete? | -- | -- | |
Does the fuel tank pressure remain at or above the specified value while the EVAP SYSTEM SEAL ON? | 2500 RPM 0 in. H2O | |||
12 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
13 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
