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
- No MAP sensor DTCs.
- No TP sensor DTCs.
- No VSS DTCs.
- No HO2S DTCs.
- No ECT DTCs.
- The DTC P0125 not active.
- No IAT sensor DTCs.
- No Fuel Level DTCs.
- The Fuel Level is greater than 12.5% and 87.5%.
- Vacuum decay for a period of at least 15 seconds.
- Vacuum less than 7 in. H2O for a time less than 25 seconds.
- Vacuum greater than .1 in. H2O for a time no more than 35 seconds.
Cold Start Test
| • | The ECT is greater than 3.75°C but less than 30°C. |
| • | The IAT is greater than 3.75°C but less than 30°C. |
| • | Start up ECT is not more than 8.25°C greater than the start up IAT. |
| • | Start up IAT is not more than 1.5°C greater than the start up ECT. |
| • | The Baro is greater than 75 kPa. |
| • | Fuel level input test has passed. |
Fuel Slosh Test
| • | The change in fuel tank vacuum is greater than .6 in. H2O. |
| • | The fuel level change is greater than 7.8%. |
Weak Vacuum Test
| • | TP less than 75%. |
| • | Vehicle speed less than 65 mph. |
| • | Fuel tank vacuum is at least 9 in. H2O within 12.5 seconds. |
Action Taken When the DTC Sets
| • | The VCM illuminates the MIL during the second key cycle in which the DTC sets. |
| • | The VCM stores the conditions which were present when the DTC sets as the Freeze Frame and the 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 the EVAP canister fuel vapor and purge line fittings |
| • | A cracked or punctured EVAP canister |
| • | A damaged source vacuum line, an EVAP purge line, a 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 |
| - | A 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. |
| • | A missing or damaged weather-pack on the EVAP Purge Solenoid connector. |
Refer to Carbon Particle Removal from EVAP System before starting the repairs.
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
-
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.
-
This step verifies that the fuel tank pressure accurately reacts to EVAP system pressure changes.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool to record the Freeze Frame and the Failure Records for reference. This data will be lost when the Clear Info function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||
Is the Fuel Tank Pressure at the specified value? | 0 in. H2O ±1 in. H2O | |||||||||
|
Important: Before continuing with the diagnosis, zero the EVAP Pressure and Vacuum gauges on the Enhanced EVAP Pressure Purge Diagnostic Cart J 41413. Refer to tool operating instructions.
Is the Fuel Tank Pressure at the specified value? | 5 in. H2O 5 in. H2O (±1 in. H2O | |||||||||
4 |
Does the pressure decrease to less than the specified value within 2 minutes? | 15 in. H2O 10 in. H2O | Refer to Diagnostic Aids | |||||||
5 |
Can the specified vacuum be maintained? | 5 in. Hg | ||||||||
6 |
Was a problem found? | -- | ||||||||
7 | Replace the EVAP vent valve. Refer to Diagnostic Aids. Refer to EVAP Vent Valve Replacement . Is action complete? | -- | -- | |||||||
8 |
Was a problem found? | -- | ||||||||
9 |
Is the action complete? | -- | -- | |||||||
10 |
Does the pressure decrease to less than the specified value within 2 minutes? | 15 in. H2O 10 in. H2O | System OK |
