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 Setting the DTC
| • | The BARO is greater than 75 kPa. |
| • | The intake air temperature is between 5°C and 29°C (41°F and 84°F) at engine start up. |
| • | The engine coolant temperature is between 5°C and 29°C (41°F and 84°F) at engine start up. |
| • | The Intake Air Temperature is not more than 1°C (2°F) greater than the Engine Coolant Temperature at start up. |
| • | The Engine Coolant Temperature is not more than 7°C (12°F) greater than the Intake Air Temperature at start up. |
| • | The fuel tank level is between 26 percent and 74 percent. |
| • | The TP sensor is between 7 percent and 35 percent. |
| • | The EVAP solenoid is at 50 percent PWM within 65 seconds of the engine run time. |
| • | The EVAP System detects a vacuum and is unable to release the vacuum during the diagnostic test. |
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134 and P1133 are not set. |
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
Although this DTC is considered a type A diagnostic, this DTC acts like a type B diagnostic under certain conditions. Refer to Serial Data Communications . Whenever this diagnostic reports that the system has passed, or if the battery is disconnected, the diagnostic must fail twice before setting a DTC. The initial failure does not report to the diagnostic executive or display on a scan tool. A passing system always reports to the diagnostic executive immediately.
If a DTC P0460 is set along with an EVAP System DTC, the EVAP DTC cannot be considered valid until you repair and clear DTC P0460.
Check for the following conditions:
| • | A poor connection at the PCM. Inspect the harness connectors for the following conditions: |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed connectors |
| - | Damaged terminals |
| - | A poor terminal to wire connection |
| • | A damaged harness. Inspect the wiring harness to the EVAP vent 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 canister and the EVAP vent solenoid is not restricted. |
| • | Refer to Evaporative Emission System Cleaning for further procedure. |
Test Description
The number(s) below refer(s) to the step number(s) 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 or P0460 also set? | -- | Go to Component 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? | 0 mmHg (±2.4 mmHg) | 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 12 mmHg (±4.8 mmHg) | 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 | Refer 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 Diagnostic Aids. Is the action complete? | -- | -- | |
10 | Replace the EVAP canister. Refer to Diagnostic Aids. 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 applicable DTC table | System OK |
