Circuit Description
The EVAP vacuum switch is a normally closed switch positioned in the purge line between the canister and the EVAP purge valve. 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 vacuum switch signal to determine if the evaporative emission control system is working properly. If the EVAP vacuum switch signal circuit is open when vacuum sufficient to open the EVAP vacuum switch should not be present, DTC P1442 will set.
Conditions for Setting the DTC
| • | No active TP sensor, IAT sensor, MAP sensor, MAF sensor 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.
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The EVAP vacuum switch is normally closed when no vacuum is present. With the key ON and the engine not running, there shouldn't be any vacuum present in the EVAP system.
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Determines if the PCM is able to control the EVAP purge solenoid valve.
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Determines if the DTC will set under the conditions present when the DTC was originally stored. If not, the fault is intermittent.
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This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||
With the ignition ON, engine not running, observe EVAP Vacuum Sw. display on the scan tool. Does EVAP Vacuum Sw. display No Purge? | -- | |||||||||
Does the scan tool indicate DTC P1442 failed? | -- | Refer to DTC P1442 Diagnostic Aids | ||||||||
Does EVAP Vacuum Sw. display No Purge? | -- | |||||||||
5 |
Was a problem found? | -- | ||||||||
6 |
Was a problem found? | -- | ||||||||
Replace the PCM. Important:: The replacement PCM must be programmed. Go to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||||||||
8 |
Was a problem found? | -- | ||||||||
9 |
Was a problem found? | -- | ||||||||
10 | Replace the EVAP vacuum switch. Go to Evaporative Emission Vacuum Switch . Is action complete? | -- | -- | |||||||
11 |
Does EVAP Vacuum Sw. display No Purge? | -- | System OK |
