Circuit Description
Canister purge is controlled by an EVAP purge valve that allows manifold vacuum to purge the canister. The Powertrain Control Module (PCM) supplies a ground to energize the EVAP purge valve (purge ON ). The EVAP purge valve control is Pulse Width Modulated (PWM) or turned ON and OFF several times a second. The PCM controlled PWM output is commanded when the following conditions have been met:
| • | Engine coolant temperature above 60°C (140°F). |
| • | After the engine has been running about 3 minutes on a cold start or 20 seconds on a warm start. |
Canister purge PWM duty cycle varys according to operating conditions determined by mass air flow, fuel trim, and intake air temperature.
Canister purge operation is also affected by throttle position.
| • | VIN 1 -- Canister purge will be disabled if TP angle increases to above 33 percent. Canister purge will be re-enabled when TP angle decreases below 29 percent. |
| • | VIN K -- Canister purge will be disabled if TP angle increases to above 70 percent. Canister purge will be re-enabled when TP angle decreases below 66 percent. |
The EVAP vacuum switch is a normally closed switch positioned in the purge line between the canister and the EVAP purge valve. The EVAP vacuum switch will open when vacuum increases to greater than 5 inches of water (in H2O) in the purge line. The PCM monitors the EVAP vacuum switch signal to determine if the evaporative emission control system is working properly. If the switch is open (purge flow detected) when the PCM is not commanding the EVAP purge valve ON, DTC P1441 will be set.
Conditions for Setting the DTC
| • | No active EVAP vacuum switch, TP sensor, IAT sensor, MAP sensor, or ODM DTC(s) set. |
| • | BARO reading is greater than 70 kPa. |
| • | Engine speed is between 650-5,000 RPM. |
| • | Intake Air Temperature is between 10-70°C (50-158°F). |
| • | The difference between Engine Coolant Temperature and Intake Air Temperature is less than 10°C (18°F). |
| • | EVAP Purge PWM is less than 3 percent. |
| • | The EVAP vacuum switch is open. |
| • | The above conditions are present for longer than 4 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed. |
| • | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool. |
Diagnostic Aids
Check for the following conditions:
| • | Poor connection at the PCM. |
| Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. If the harness appears to be OK, observe the EVAP vacuum switch display on the scan tool while moving connectors and wiring harnesses related to the switch. A change in the display will indicate the location of the fault. |
| • | Incorrect vacuum hose routing. |
| Verify that the vacuum hose routing to the canister purge vacuum switch and the canister purge solenoid is correct and that the vacuum hoses to the canister purge solenoid are not switched. |
| • | Restricted fuel vapor line, purge hose, canister vent, or blocked canister. |
| A condition that causes the EVAP system to trap vacuum can keep the EVAP vacuum switch open, causing DTC P1441 to be set. |
| • | Faulty or damaged canister. |
| A faulty canister may intermittenly allow charcoal into the EVAP purge solenoid, vacuum switch, and associated lines causing a DTC to be set. Use the following procedure to check for a carbon release condition: |
| 1. | Turn OFF the ignition switch. |
| 2. | Remove the EVAP purge solenoid. Refer to Evaporative Emission Canister Purge Solenoid . |
| 3. | Remove the EVAP vacuum switch. Refer to Evaporative Emission Vacuum Switch . |
| 4. | Lightly tap the purge solenoid and (if applicable) the vacuum switch on a clean work area looking for carbon particles exiting either of the vacuum ports. |
| 5. | If no carbon release is evident, reinstall the components and continue with the DTC P1441 diagnostic table. If carbon is being released from either component, continue with this service procedure. |
| 6. | Remove the charcoal canister from the vehicle. |
| 7. | Ensure that the main cylinder valve is turned off on the
|
| 8. | Disconnect the black hose that connects the nitrogen cylinder to the EVAP purge/pressure diagnostic station at the pressure regulator by unscrewing the knurled nut on the regulator. No tools are required to remove the black hose from the regulator. |
| 9. | Using a section of vacuum line, connect one end over the open threaded fitting of the EVAP purge/pressure diagnostic station pressure regulator. |
| 10. | Connect the remaining end to the purge solenoid end of the EVAP purge line at the vehicle and turn on the main nitrogen cylinder valve. Continue to blow any debris from the purge line for 15 seconds. |
| 11. | Return the EVAP Pressure/Purge Diagnostic Station to its original condition by re-installing the black hose that was disconnected in step 8. |
| 12. | Replace the following components: |
| • | The EVAP purge solenoid. Refer to Evaporative Emission Canister Purge Solenoid . |
| • | The EVAP canister. Refer to Evaporative Emission Canister Replacement . |
| • | The EVAP vacuum switch. Refer to Evaporative Emission Vacuum Switch . |
| 13. | Proceed with the DTC P1441 diagnostic table. |
Reviewing the Fail 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
Number(s) below refer to the step number(s) on the Diagnostic Table.
-
The canister purge vacuum switch is normally closed when no vacuum is present. With the ignition switch ON and the engine not running, there should not be any vacuum applied to the EVAP system.
-
Determines if the PCM is able to control the EVAP purge solenoid valve.
-
Determines if the DTC will set under the conditions present when the DTC was originally stored. If not, the fault is intermittent.
-
Checks for a grounded EVAP purge solenoid control circuit, a faulty EVAP vacuum switch, or a leaking EVAP purge solenoid valve.
-
Checks for an open EVAP vacuum switch.
-
This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||
Does EVAP Vacuum Sw. display No Purge? | -- | |||||||||
Does EVAP Vacuum Sw. display No Purge with the EVAP purge solenoid commanded OFF? | -- | |||||||||
Does the scan tool indicate DTC P1441 failed? | -- | Refer to Diagnostic Aids | ||||||||
Does EVAP Vacuum Sw. display No Purge? | -- | |||||||||
6 |
Was a problem found? | -- | ||||||||
7 |
Is the vacuum greater than the specified value? | 5 inches H2O | ||||||||
8 |
Was a problem found? | -- | ||||||||
9 | Replace the EVAP purge solenoid. Refer to Evaporative Emission Canister Purge Solenoid . Is Action complete? | -- | -- | |||||||
10 |
Was a problem found? | -- | ||||||||
11 |
Was a problem found? | -- | ||||||||
Does EVAP Vacuum Sw. display No Purge? | -- | |||||||||
13 |
Was a problem found? | -- | ||||||||
14 |
Was a problem found? | -- | ||||||||
15 | Replace the EVAP vacuum switch. Refer to Evaporative Emission Vacuum Switch . Is Action complete? | -- | -- | |||||||
Replace the PCM. Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is Action complete? | -- | -- | ||||||||
17 |
Does the scan tool indicate DTC P1441 failed? | -- | System OK |
