Refer to
EVAP and EGR Controls
for wiring view.
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). The duty cycle (pulse width) is determined by Closed Loop feed back from the Oxygen Sensor 1 (O2S 1). 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 in. 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 control system is working properly. If the switch is OFF (no purge detected) when the PCM is commanding purge, a DTC will be set.
Conditions for Setting the DTC
| • | Vacuum is less than 4.5V. |
| • | The BARO is greater than 83kPa. |
| • | The MAP is greater than 20kPa and less than 70kPa. |
| • | The engine coolant temperature is between 4°C (39°F) and 30°C (86° F) at engine start up. |
| • | The intake air temperature is between 2°C (36°F)and 30°C (86°F) at engine start up. |
| • | ECT and IAT are within 6°C (43°F) of one another. |
| • | The throttle position angle is between 9% and 20%. |
| • | The engine run time is less than 1300 seconds. |
| • | The engine speed is between 1700 and 4000 RPM. |
| • | One or more of the following DTCs are not set P0107, P0108, P0122, P0123 not set. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) illuminates. |
| • | The PCM records the operating conditions at the time when the diagnostic fails. This information stores in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
| • | The coolant fan turns ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | The MIL/DTCs can be cleared by using the scan tool. |
Diagnostic Aids
Make a visual check of vacuum hose(s). Check throttle body for possible cracked, broken, or plugged vacuum block. Check 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 Intermittents, in Symptoms.
Refer to Carbon Particle Removal from EVAP System for further procedures.
Test Description
Number(s) below refer to the step number(s) 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 gauge.
-
Whenever 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 couldn't 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 | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
Does the EVAP canister purge valve turn ON when commanded? | -- | |||
Did the vacuum gage indicate the specified vacuum or more while snapping the throttle? | 2500 RPM 10Hg (34kPa) | Go to Diagnostic Aids | ||
Did the test light illuminate? | -- | |||
Does EVAP Vacuum Switch indicate ON? | -- | |||
6 |
Does the test light flash ON when the purge valve is commanded ON? | -- | ||
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? | -- | ||
9 | Check the EVAP vacuum switch signal circuit for a short to the voltage and repair as necessary. Was a repair necessary? | -- | ||
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? | -- | ||
14 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
15 | Check to see if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
