Circuit Description
Canister purge is controlled by a solenoid valve that allows manifold vacuum to purge the canister. The Powertrain Control Module (PCM) supplies a ground to energize the solenoid valve (purge ON). The EVAP purge solenoid control is Pulse Width Modulated (PWM) or turned ON and OFF several times a second. The duty cycle (pulse width) is determined by engine operating conditions including load, throttle position, coolant temperature and ambient temperature. The duty cycle is calculated by the PCM and the output is commanded when the appropriate conditions have been met.
The EVAP purge vacuum switch is a normally closed switch positioned in the purge line between the canister and the EVAP purge solenoid. The EVAP purge vacuum switch will open when vacuum increases to greater than 5 inches of water in the purge line. The PCM monitors the EVAP purge vacuum switch signal to determine if the evaporative emission control system is working properly. If the switch is open when sufficient vacuum should not be present, DTC P1442 will be set.
Conditions for Setting the DTC
| • | No active TP sensor, IAT sensor, MAP sensor, or Output Driver DTC(s) set. |
| • | Intake Air Temperature is between 0°C (32°F) and 70°C (158°F). |
| • | The EVAP purge vacuum switch is open during key ON (before the engine is cranked). |
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 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 sensor. A change in the display will indicate the location of the fault. |
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 (purge) is present. With the key ON and the engine OFF, there should not be any vacuum (purge) present in the EVAP system.
-
Checks if the PCM is able to control the EVAP purge solenoid valve.
-
Checks if the DTC will set under the conditions present when the DTC was originally stored. If not, the fault is intermittent.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic System Check performed? | -- | Go to Powertrain OBD System Check | |||||||
With the ignition ON, engine not running, observe EVAP Vacuum Sw. display on the scan tool Engine 1 data list. Does EVAP Vacuum Sw. display Closed? | -- | |||||||||
Does scan tool indicate DTC P1442 failed? | -- | Refer to Diagnostic Aids | ||||||||
Does EVAP Vacuum Sw. display No Purge? | -- | |||||||||
5 |
Was a problem found? | -- | ||||||||
6 |
Was a problem found? | -- | ||||||||
7 | Replace the PCM. Important: Replacement PCM must be programmed. Refer to PCM Replacement/Programming. Is action complete? | -- | -- | |||||||
8 | Replace EVAP vacuum switch. Is action complete? | -- | -- | |||||||
9 |
Does EVAP Vacuum Sw. display No Purge? | -- | Repair complete |
