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 (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 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 set.
Conditions for Setting the DTC
| • | EVAP vacuum switch indicates OFF when the EVAP purge valve is commanded to 100%. |
| • | BARO is greater than 84 kPa. |
| • | MAP is greater than 40 kPa and less than 75 kPa. |
| • | ECT is less than 105°C. |
| • | IAT is greater than 2°C. |
| • | TP is between 10% and 22%. |
| • | Engine run time is less than 1300 seconds. |
| • | Engine speed is between 1700 and 5000 RPM. |
| • | DTCs P0107, P0108, P0122, and P0123 not set. |
Action Taken when the DTC Sets
Malfunction indicator lamp (MIL) illuminates after two consecutive driving cycle with the fault active.
Conditions for Clearing the 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 DTC(s) can be cleared by using a 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 check for backed out terminals, improper mating, broken locks, improper formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness.
Refer to Intermittents, in Symptoms, Section 6E3-B.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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When commanded by the scan tool, the EVAP canister purge valve should make a "clicking" noise. This verifies if the PCM has control of purge valve.
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The EVAP vacuum switch normally displays OFF when no vacuum (purge) is present. With the key ON and the engine OFF, there shouldn't be any vacuum (purge) present in the EVAP system.
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Determine if the reason the EVAP canister purge valve could not be commanded was the result of a faulty purge valve, faulty wiring or faulty PCM.
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Determine if the vacuum switch, wiring or PCM is at fault.
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The PCM supplies a 5-volt reference to the vacuum switch on CKT 416. This step determines if the wiring or the PCM is at fault.
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If the 5-volt reference was not available to the vacuum switch and no other DTCs were set, then the connection is faulty or the circuit is open between the sensor and the wiring splice from the 5-volt reference circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
Was the On-Board Diagnostic (OBD) System Check perform? | -- | Go to Step 2 | ||
Install scan tool, view DTC screens. Is a MAP sensor DTC also set? | -- | Go to MAP DTC Chart | Go to Step 3 | |
Does the EVAP canister purge valve turn ON when commanded? | -- | Go to Step 4 | Go to Step 5 | |
View Engine 1 screens. Does scan tool display EVAP Vac Switch ON? | -- | Go to Step 6 | Go to Diagnostic Aids | |
Does the test light flash ON when the purge valve is commanded ON? | 0.5 ohms | Go to Step 7 | Go to Step 8 | |
6 |
Does scan tool display EVAP Vac Switch OFF? | -- | Go to Step 10 | Go to Step 11 |
7 | Replace EVAP canister purge valve. Is action complete? | -- | -- | |
8 | Check the EVAP purge valve driver circuit for a short to ground and repair as necessary. Was a repair necessary? | -- | Go to Step 9 | |
9 | Replace the PCM. Is action complete? | -- | -- | |
10 | Check for poor connection at the EVAP vacuum switch connector and repair as necessary. Was a repair necessary? | -- | Go to Step 12 | |
11 | With DVM connected to ground, probe the 5-volt reference circuit. Is voltage near the specified value? | 5.0 V | Go to Step 13 | Go to Step 14 |
12 | Replace EVAP vacuum switch. Is action complete? | -- | -- | |
13 | Check vacuum signal circuit for an open or poor connection and repair as necessary. Was a repair necessary? | -- | Go to Step 9 | |
Repair open or poor connection in the vacuum switch 5-volt reference circuit. Is action complete? | -- | -- | ||
