Circuit Description
The evaporative system (EVAP) includes the following components:
| • | The fuel tank |
| • | The EVAP vent solenoid |
| • | Fuel tank pressure sensor |
| • | The fuel pipes and hoses |
| • | The fuel vapor lines |
| • | The fuel cap |
| • | The EVAP canister |
| • | The purge lines |
| • | The EVAP canister purge solenoid valve |
| • | The EVAP service port |
The EVAP system is checked by applying vacuum to the EVAP system and by monitoring for a vacuum decay. The Powertrain Control Module (PCM) monitors the vacuum level through the fuel tank pressure sensor signal. At an appropriate time, the EVAP canister purge solenoid valve and the EVAP vent solenoid are turned ON, allowing the engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP canister purge solenoid valve is turned OFF, sealing the system.
A restricted or blocked EVAP canister vent path is detected by drawing a vacuum on the EVAP system, turning OFF the EVAP vent solenoid and the EVAP canister purge solenoid valve, with the EVAP vent solenoid open and the EVAP purge pulse width modulation (PWM) 0 percent, and monitoring the fuel tank vacuum sensor signal. With the EVAP vent solenoid open, any vacuum in the system should decrease quickly unless the vent path is blocked. A blockage can be caused by the following conditions:
| • | A malfunctioning EVAP vent solenoid, stuck closed |
| • | The vent hose for the following conditions: |
| - | Plugs |
| - | Kinks |
| - | Pinches |
| • | A shorted EVAP vent solenoid driver circuit |
| • | A plugged evaporative canister |
If any of these conditions are present, DTC P0446 will set.
Conditions for Running the DTC
| • | No active MAP DTC's |
| • | No active IAT DTC's |
| • | No active ECT DTC's |
| • | No active TP DTC's |
| • | No active Oxygen Sensor DTC's |
| • | No active Fuel Tank Pressure DTC's |
| • | No active VSS DTC's |
| • | No active PCM Memory DTC's |
| • | The BARO is more than 75 kPa. |
| • | The Start-up ECT and IAT are between 4°C and 30°C (39°F and 86°F). |
| • | The Start-up ECT is less than 8°C (14°F) above Start-up IAT. |
| or |
| The Start-up IAT is less than 1.5°C (3°F) above Start-up ECT. |
| • | The fuel level is between 15 percent and 85 percent. |
| • | The TP sensor is between 7 percent and 35 percent. |
| • | The Vehicle Speed is less than 70MPH (113KPH). |
| • | The engine is running. |
Conditions for Setting the DTC
The EVAP system is unable to release vacuum during the diagnostic test.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information. |
| • | The EVAP purge function is disabled until the diagnostic passes. |
| • | A history DTC stores. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs a pass. |
| • | A history DTC will clear after 40 consecutive warm up cycles without a malfunction. |
| • | A scan tool can clear the DTCs. |
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 to the EVAP vent solenoid and the fuel tank pressure sensor for an intermittent open or short circuit. |
| • | Kinked, pinched or plugged vent hose: Verify that the vent hose between the canister and the EVAP vent solenoid is not restricted. |
Check for charcoal particles. Refer to Evaporative Emission System Cleaning before starting repairs.
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that causes the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
-
The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.
-
If a vent solenoid electrical malfunction is present, the purge system will not operate correctly. Repairing the electrical malfunction will very likely correct the condition that set DTC P0446.
-
This step checks the fuel tank pressure sensor at the ambient pressure.
-
This step verifies that the fuel tank pressure sensor accurately reacts to the EVAP system pressure changes.
-
This step checks for a blocked EVAP canister.
-
This step duplicates the Powertrain On-Board Diagnostic test.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
2 |
Is DTC P0452, P0453, P0460, P0462 or P0463 also set? | -- | Go to applicable DTC table | |
Does the purge valve and the vent solenoid click when commanded ON and OFF? | -- | |||
Is the fuel tank pressure at the specified value? | -2.4 to 2.4 mmHg (-1.28 to 1.28 in. H2O) | Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage or | ||
|
Important: : Before continuing with the diagnosis, zero the EVAP Pressure and Vacuum gauges on the EVAP pressure/purge cart J 41413 . Refer to tool operating instructions.
Important: Do not exceed the pressure in the first specified value. Is the fuel tank pressure at the second specified value? | 12 mmHg (6.42 in. H2O) 7.2 to 16.8 mmHg (3.85 to 8.99 in. H2O) | Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage or | ||
6 |
Does the EVAP pressure return to the second specified value within 5 seconds? | 5 in. H2O 0 in. H2O | Go to Diagnostic Aids | |
Does the vacuum remain below the second specified value? | 2500 RPM 10 in. H2O | |||
8 |
Were there any necessary repairs? | -- | ||
9 | Replace the EVAP vent solenoid. Refer to Evaporative Emission Vent Valve Replacement . Is the action complete? | -- | -- | |
10 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Is the action complete? | -- | -- | |
Does the EVAP pressure return to the second specified value within 5 seconds? | 5 in. H2O 0 in. H2O | |||
12 |
Does the scan tool indicate that the diagnostic ran and passed? | -- | ||
13 | Check to see if any additional DTC are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
