P0442

Diagnostic Chart:

Wiring Diagram:

****TSB Update 77-65-08, Feb. 1997, EVAP Vent Valve plunger may be trapped (sometimes intermittently) by the plunger spring. Refer to EVAP Vent Valve. An improved EVAP Vent Valve (P/N 12559015) has been put into production and release for service.****

Circuit Description
The evaporative system includes the following components:

^ The fuel tank
^ The EVAP vent solenoid
^ The fuel tank pressure sensor
^ The fuel pipes and hoses
^ The vapor lines
^ The fuel cap
^ The evaporative emission canister
^ The purge lines
^ The EVAP purge solenoid

The evaporative leak detection diagnostic strategy is based on applying a vacuum to the EVAP system and monitoring the vacuum decay. The VCM monitors vacuum level via the fuel tank vacuum sensor input. At an appropriate time, the EVAP purge solenoid and the EVAP vent solenoid are turned on, allowing the engine vacuum to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP purge solenoid turns OFF sealing the system. A leak is detected by monitoring for a decrease in the vacuum level over a given time period with all other variables remaining constant. A small leak in the system will cause DTC P0442 to be set. This DTC is a Type A DTC.

Conditions for Setting the DTC
1. No MAP sensor DTCs
2. No Throttle Position (TP) sensor DTCs
3. No Vehicle Speed Sensor (VSS) DTCs
4. No HO2S DTCs
5. No ECT DTCs
6. The DTC P0125 not active
7. No IAT sensor DTCs
8. No Fuel Level DTCs
9. The Fuel Level is greater than 12.5% and 87.5%
10. A vacuum decay for a period of at least 15 seconds
11. A vacuum less than 7 in. H2O for a time less than 25 seconds
12. A vacuum greater than 0.1 in. H2O for a time less than 35 seconds

Cold Start Test

^ The ECT is greater than 3.75°C (38.75°F) but less than 30°C (86°F).
^ The IAT is greater than 3.7°C (38.75°F) but less than 30°C (86°F).
^ Start up ECT is not more than 8.25°C (46.85°F) greater than the start up IAT.
^ Start up IAT is not more than 1.5°C (34.7°F) greater than the start up ECT.
^ The Baro is greater than 75 kPa.
^ The fuel level input test has passed.

Fuel Slosh Test

^ The change in the fuel tank vacuum is greater than 0.6 in. H20.
^ The fuel level change is greater than 7.8%.

Weak Vacuum Test

^ The Throttle Position (TP) is less than 75%.
^ The Vehicle speed is less than 65 mph.
^ The fuel tank vacuum is at least 9 in. H20 within 12.5 seconds.

Action Taken When the DTC Sets

^ The VCM illuminates the Malfunction Indicator Lamp (MIL) during the second key cycle in which the DTC sets.
^ The VCM stores the conditions which were present when the DTC set as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC
The following conditions will clear the DTC:

^ The VCM turns the MIL off on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
^ A history DTC clears after 40 consecutive warm-up cycles have occurred without a fault.
^ The scan tool Clear Info function or disconnecting the VCM battery feed can clear the DTC.

Diagnostic Aids
Check for the following conditions:

^ Damaged O-rings at EVAP canister fuel vapor and purge line fittings
^ A cracked or punctured EVAP canister
^ A damaged source vacuum line, EVAP purge line, vent hose or fuel tank vapor line
^ A poor connection at the VCM: Inspect the harness connectors for the following conditions:

- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wire connection

^ A damaged harness: Inspect the wiring harness to the EVAP vent solenoid EVAP purge solenoid and the fuel tank pressure sensor for an intermittent open or short circuit.
^ Missing or damaged weather-pack on the EVAP Purge Solenoid connector

Refer to Carbon Particle Removal from EVAP System before starting repairs. Service and Repair

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.

Test Description
The numbers below refer to the step numbers on the diagnostic table

2. This step checks the fuel tank pressure sensor at ambient pressure. The fuel tank pressure sensor is zeroed at every key on to compensate for changes in atmospheric pressure.
3. This step verifies that the fuel tank pressure accurately reacts to EVAP system pressure changes.