Circuit Description
The evaporative system includes the following components:
| • | The Fuel Tank |
| • | The EVAP Vent Valve |
| • | The Fuel Tank Pressure sensor |
| • | The Fuel Pipe and hoses |
| • | The Vapor Lines |
| • | The Fuel Cap |
| • | The EVAP Canister |
| • | The Purge Line |
| • | The EVAP Purge Solenoid |
The following items detect a restricted or blocked EVAP Canister vent path:
| • | Drawing a vacuum into the EVAP system |
| • | Turning OFF the EVAP Vent Valve and the EVAP Purge Solenoid (EVAP Vent Valve Open, the EVAP Purge Solenoid PWM 0%) |
| • | Monitoring the Fuel Tank Pressure sensor input |
With the EVAP Vent Valve open, any vacuum in the system should decrease quickly unless the vent path is blocked. The following conditions can cause a blockage:
| • | A malfunctioning EVAP Vent Valve (stuck closed) |
| • | A plugged kinked or pinched vent hose |
| • | A shorted EVAP Vent Valve Driver circuit |
| • | A plugged EVAP Canister. |
If any of these conditions are present, a DTC P0446 set.
Conditions for Running the DTC
| • | No active MAP sensor DTCs |
| • | No active TP sensor DTCs |
| • | No active VS sensor DTCs |
| • | No active O2 sensor DTCs |
| • | No active ECT sensor DTCs |
| • | No active IAT sensor DTCs |
| • | DTC P0125 not active |
| • | The fuel level is between 12.5-87 %. |
| • | The system voltage is between 10-17 volts. |
| • | The ECT is between 4°C-30°C (39°F-86°F). |
| • | The IAT is between 4°C-30°C (39°F-86°F). |
| • | The cold start temperature difference (ECT minus IAT) is less than |
| - | 1.5°C(35°F) when the IAT is greater than the ECT or |
| - | 8°C(46°F) when the ECT is greater than the IAT |
| • | The BARO is greater than 72 kPa. |
| • | The change in fuel tank vacuum is less than 0.6 in. of H2O, or the change in fuel level is less than 8 %. |
| • | The fuel tank vacuum level remains above a calibrated value for a specified number of seconds. |
Conditions for Setting the DTC
The VCM fails to detect a drop in the EVAP system vacuum over a calibrated number of seconds with the vent solenoid open.
Action Taken When the DTC Sets
| • | The VCM illuminates the MIL during the first key cycle in which the DTC sets. |
| • | The VCM stores the conditions which were present when the DTC sets as a Freeze Frame and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after one ignition cycle in which the diagnostic runs without a fault. |
| • | The Freeze Frame information and the history DTC will clear after one ignition cycle in which the diagnostic runs without a fault. |
| • | A scan tool can clear the DTC(s). |
Diagnostic Aids
Check for the following conditions:
| • | 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 connections |
| • | A damaged harness: Inspect the wiring harness to the EVAP Vent Valve, EVAP Purge Solenoid and the Fuel Tank Pressure sensor for an intermittent open or short circuit. |
| • | A kinked, pinched or plugged vent hose. Verify that the vent hose between the EVAP Canister and the EVAP Vent Valve is not restricted. |
Refer to Symptoms before starting 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 be set occurs. This may assist in diagnosing the condition.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
This step checks the Fuel Tank Pressure sensor at atmospheric pressure.
-
This step verifies that the Fuel Tank Pressure sensor accurately reacts to EVAP system pressure changes.
-
Checks for a blocked EVAP Canister.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and the Failure Records for reference. This data will be lost when the Clear DTC Information function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Is the Fuel Tank Pressure at the specified value? | -1-1 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 the tool operating instructions.
Does the scan tool indicate the fuel tank pressure at the second specified value? | 5 in.H2O 4-5 in.H2O | |||
4 |
Does the EVAP pressure return to the second specified value within 10 seconds? | 5 in.H2O -1-1 in.H2O | Refer to Diagnostic Aids | |
Can the specified value of vacuum be obtained? | 5 in.Hg | |||
6 |
Was a problem found? | -- | ||
7 |
Is test light ON. | -- | ||
8 |
Is the test light ON? | -- | ||
9 | Repair short to ground in EVAP Vent Control circuit. Refer to Wiring Repairs in Repair Instructions. Is the action complete? | -- | -- | |
10 | Replace the EVAP Vent Valve. Refer to Diagnostic Aids. Refer to EVAP Vent Valve Replacement (EVAP) in Repair Instructions. Is the action complete? | -- | -- | |
11 | Replace EVAP Canister. Refer to Diagnostic Aids. Refer to Evaporative Emission Canister Replacement in Repair Instructions. Is the action complete? | -- | -- | |
12 |
Is the action complete? | -- | -- | |
13 |
Does the EVAP pressure return to the second specified value within 10 seconds? | 5 in.H2O 0 in.H2O | ||
14 |
Was the test performed and passed? | -- | ||
15 | Use the scan tool in order to display the Capture Info and the Review Capture Info functions. Are there any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
