Circuit Description
Canister purge is controlled by a purge valve that allows ported vacuum to purge the canister when energized. The powertrain control module (PCM) supplies a ground to energize the purge valve, purge ON. The purge valve control by the PCM is pulse width modulated (PWM) or turned ON and OFF several times a second. The duty cycle, or pulse width is determined by Closed Loop feed back from the oxygen sensor (O2S). The duty cycle is calculated by the PCM and the output is commanded when certain conditions have been met.
A vacuum switch in the purge line is used to detect when the system is being purged. The normally closed switch will open when 5 inch H2O or more is present in the purge line. The PCM supplies a 5-volt reference to the switch to monitor if the Evaporative Emission (EVAP) Control System is working properly. If the switch is OFF or no purge is detected when the PCM is commanding purge, a DTC will be set.
Conditions for Setting the DTC
| • | The EVAP vacuum switch indicates OFF when the EVAP purge valve is commanded to 100 percent. |
| • | The BARO is more than 84 kPa. |
| • | The manifold absolute pressure (MAP) is more than 40 kPa and less than 75 kPa. |
| • | The engine coolant temperature (ECT) is less than 105°C (221°F). |
| • | The intake air temperature (IAT) is more than 2°C (35.6°F). |
| • | The throttle position (TP) is between 10-22 percent. |
| • | The engine run time is less than 1,300 seconds. |
| • | The engine speed is between 1,700-5,000 RPM. |
| • | DTCs P0107, P0108, P0122, and P0123 are not set. |
Action Taken When the DTC Sets
The malfunction indicator lamp (MIL) illuminates after two consecutive driving cycles with the fault active.
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after passing three consecutive diagnostic tests. |
| • | A history DTC will clear after 40 consecutive ignition cycles have occurred without a fault. |
| • | History and current DTCs can be cleared by using a scan tool. |
Diagnostic Aids
| • | Make a visual check of the vacuum hoses. check the throttle body for possible cracked, broken, or plugged vacuum block. Check the engine for a possible mechanical problem. |
| • | An intermittent problem may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation. |
| • | Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness. |
| • | Refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The purge valve will click when commanded ON by the scan tool. This determines if the PCM can control the purge valve.
-
Ported, off idle vacuum is used at the purge valve. Vacuum will only be seen off idle with a vacuum gage.
-
If voltage is not available to the purge valve, the PCM will not be able to command the purge valve ON.
-
Disconnecting the vacuum switch electrical connector opens the 5-volt reference circuit from the PCM which indicates that purge is present. Leaving the switch disconnected will cause a DTC P1441.
-
Determines if the purge valve could not be commanded due to an electrical circuit problem or faulty purge valve. If the test light remains ON steady, check the EVAP driver circuit for a short to ground. If the test light is OFF, check the EVAP driver circuit for an open or short to voltage.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Was the On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | |
Does the EVAP canister purge valve turn ON when commanded? | -- | Go to Step 3 | Go to Step 4 | |
Did the vacuum gage indicate the specified vacuum or more while snapping the throttle? | 2,500 RPM 10 in Hg (34 kPa) | Go to Step 5 | Go to Diagnostic Aids | |
Did the test light illuminate? | -- | Go to Step 6 | Go to Step 7 | |
Does the EVAP Vac Switch indicate ON? | -- | Go to Step 8 | Go to Step 9 | |
Does the test light flash ON when the purge valve is commanded ON? | -- | Go to Step 12 | Go to Step 13 | |
7 | Repair the open ignition circuit. Is the action complete? | -- | -- | |
8 | Inspect the vacuum hoses to the vacuum switch for being pinched, kinked, or blocked and repair as necessary. Was a repair necessary? | -- | Go to Step 10 | |
9 | Check the EVAP vacuum switch signal circuit for a short to voltage and repair as necessary. Was a repair necessary? | -- | Go to Step 11 | |
10 | Replace the EVAP vacuum switch. Is the action complete? | -- | -- | |
11 | Replace the PCM. Is the action complete? | -- | -- | |
12 | Replace the EVAP canister purge valve. Is the action complete? | -- | -- | |
13 | Check the EVAP driver circuit for an open, short to ground, or voltage and repair as necessary. Was a repair necessary? | -- | Go to Step 11 |
