Circuit Description
A solenoid valve controls the canister purge. A solenoid valve allows the ported vacuum to purge the canister when energized. The Vehicle Control Module (VCM) supplies a ground 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 Closed Loop feed back from the Heated Oxygen Sensor (HO2S) determines the duty cycle (a pulse width). The VCM calculates the duty cycle, the VCM commands the output when certain conditions have been met.
A vacuum switch in the purge line detects when the system is being purged. The normally closed switch will open when less than 1 in. Hg is present in the purge line. The VCM supplies a 12 volt reference to the vacuum switch in order to monitor if the evaporative switch emission control system is working properly. If the switch is closed meaning there is nor purge detected when the VCM is commanding a purge, a DTC will set. This DTC is a type B DTC.
Conditions for Setting the DTC
Test Conditions
| • | The EVAP vacuum switch state = high vacuum for a period greater than 4 seconds. |
| • | The EVAP purge solenoid diagnostic vacuum switch DTC is not set. |
| • | No IAC DTCs set |
| • | No MAP DTCs set |
| • | No TP sensor DTCs set |
| • | No EGR DTCs set |
| • | The BARO is greater than 75 kPa. |
| • | The ECT is less than 110°C. |
| • | The IAT is less than 90°C. |
| • | The difference between the ECT and the IAT reading is less than 90°C. |
| • | The purge DC is less than 0% |
| • | The MAP is at least than 20 kPa. |
| • | The throttle position is greater than 5% but less than 60%. |
| • | The engine speed is greater than 800 RPM but is less than 3000 RPM |
Action Taken When the DTC Sets
The VCM turns the MIL ON after 2 consecutive driving cycles with the fault active.
Conditions for Clearing the MIL/DTC
The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.
Diagnostic Aids
A poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation may cause an intermittent.
Throroughly check any circuitry, that is suspected as causing the intermittent complaint, for the following conditions:
| • | 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 .
Refer to Carbon Particle Removal from EVAP System before starting repairs.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
This step checks for the possibility of vacuum being trapped in the EVAP system.
-
This step begins the checks for a bad Vacuum switch.
-
This step begins the checks for a bad EVAP Purge solenoid.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing DTCs, use the scan tool in order to record the Freeze Frame and Failure Records for reference. Using the Clear Info function will lose this data. Was the On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 | Turn the ignition ON while keeping the engine off. Does the scan tool display the EVAP Vacuum switch ON? | -- | ||
Disconnect the EVAP Vacuum Switch vacuum hose (canister side). Does the scan tool display the EVAP Vacuum switch ON? | -- | |||
Does the scan tool indicate the EVAP Vacuum switch OFF? | -- | |||
5 |
Does the DVM display a voltage near the specified value? | B+ | ||
6 | With the EVAP Vacuum switch still disconnected, probe the EVAP Vacuum switch ground circuit with a test lamp to B+. Is the test lamp on? | -- | ||
7 |
Was a problem found? | -- | ||
Does the EVAP canister purge solenoid click when commanded ON and OFF? | -- | |||
9 |
Is the test lamp on? | -- | ||
10 |
Does the test lamp flash ON and OFF? | -- | ||
11 | The DTC is an intermittent. Refer to the Diagnostic Aids. | -- | -- | -- |
12 | Repair the open in the EVAP Vacuum switch ground circuit. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
13 | Repair the open in the EVAP solenoid ignition feed circuit. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
14 |
Important: If the EVAP Canister Purge Solenoid is faulty, the EVAP Canister may be leaking charcoal. Replace the faulty EVAP Canister Purge Solenoid. Refer to Diagnostic Aids. Refer to EVAP Canister Purge Solenoid . Is the action complete? | -- | -- | |
15 |
Did charcoal particles fall from the EVAP canister? | -- | ||
16 |
Is the action complete? | -- | -- | |
17 | Check the EVAP purge solenoid control circuit for an open or short to ground. Was a problem found? | -- | ||
18 | Check the EVAP Vacuum switch control circuit for an open or short to ground. Was the problem found? | -- | ||
19 | Replace the EVAP Vacuum switch. Refer to Diagnostic Aids. Refer to EVAP Vacuum Switch . Is the action complete? | -- | -- | |
20 | Repair as necessary. Is the action complete? | -- | -- | |
21 | Replace the faulty VCM. Important: If the VCM is faulty, program the new VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
22 |
Does the scan tool indicate that this diagnostic Ran and Passed? | -- | ||
23 | Using the scan tool, select Capture Info and Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to Applicable DTC Table | System OK |
