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For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2000 🢒 Alero 🢒 Engine 🢒 Engine Controls - 2.4L 🢒 DTC P0446 Evaporative Emission (EVAP) Vent System Performance

Object Number: 621241 Size: LF
Engine Controls Components
Power, Ground, EVAP, and EGR
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice

Circuit Description

The evaporative emission (EVAP) system is tested by applying vacuum to the system and by monitoring for a vacuum decay. The PCM monitors the vacuum level through the fuel tank pressure sensor signal. At an appropriate time, the EVAP canister purge valve and the EVAP vent solenoid are turned on, allowing the engine to draw a small vacuum on the entire EVAP system. After the desired vacuum level has been achieved, the EVAP canister purge 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 valve, and monitoring the fuel tank pressure sensor signal. With the EVAP vent solenoid open, any vacuum in the system should decrease quickly unless the vent path is blocked.

The evaporative system includes the following components:

    • The EVAP canister
    • The EVAP canister purge valve
    • The EVAP service port
    • The EVAP vent valve
    • The fuel cap
    • The fuel pipes and hoses
    • The fuel tank
    • The fuel tank pressure sensor
    • The fuel vapor lines
    • The purge lines

Conditions for Running the DTC
    • The following DTCs are not set: P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0452, P0453, P0502, P0503, P0601, P0602, P1621 and P1133.
    • The barometric pressure (BARO) is more than 75 kPa.
    • The intake air temperature (IAT) is between 5°C and 29°C (41°F- 84°F) at engine start up.
    • The engine coolant temperature (ECT) is between 5°C and 29°C (41°F- 84°F) at engine start up.
    • The IAT is not more than 1°C (2°F) above the ECT at start up.
    • The ECT is not more than 7°C (12°F) above the IAT at start up.
    • The fuel tank level is between 26 percent and 74 percent.
    • The throttle position (TP) angle is between 7 percent and 35 percent.
    • The EVAP solenoid is at 40 percent PWM.

Conditions for Setting the DTC

The EVAP system is unable to release the 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.
    • 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.
    • Use a scan tool to clear the DTCs.

Diagnostic Aids

Although this DTC is considered a type A diagnostic, the DTC acts like a type B diagnostic under certain conditions. 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, P0461, P0462 or P0463 is set along with an EVAP System DTC, the EVAP DTC cannot be considered valid until you repair and clear DTC P0460, P0461, P0462 and P0463.

Any of these conditions can cause DTC P0446 to set.

Inspect the following components for the indicated conditions:

    • A poor electrical connection at the PCM. Inspect the harness connectors for the following conditions:
       - Any backed out terminals
       - Any incorrect mating
       - Any broken locks
       - Any improperly formed connectors
       - Any damaged terminals
       - A poor terminal-to-wire connection
    • A damaged wiring harness. Inspect the wiring harness to the following components for an intermittent open or short:
       - The EVAP canister purge valve
       - The EVAP vent valve
       - The fuel tank pressure sensor

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests the fuel tank pressure sensor at the ambient pressure.

    2.

  2. This step verifies that the fuel tank pressure sensor accurately reacts to the EVAP system pressure changes.

    3.

  3. This step tests for a blocked EVAP canister.

DTC P0446-Evaporative Emission (EVAP) Control System Vent Control

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Are DTC P0452, P0453, P0460, P0461, P0462 or P0463 set?

--

Go to Diagnostic Trouble Code (DTC) List/Type

Go to step 3

3

With the scan tool, command the EVAP canister purge valve and vent solenoid on and off.

Does the purge valve and the vent solenoid click when commanded on and off?

--

Go to Step 4

Go to Powertrain Control Module Outputs Diagnosis

4
  1. Turn off the ignition.
  2. Disconnect the vapor line from the fuel tank at the EVAP canister.
  3. Turn on the ignition, with the engine off.
  4. With the scan tool, observe the fuel tank pressure.

Does the fuel tank pressure equal the specified value?

-0.32 - +0.32 kPa (-1.28 - +1.28 in. H2O)

Go to Step 6

Go to Step 5

5
  1. Turn off the ignition.
  2. Inspect the EVAP vapor line from the fuel tank to the EVAP canister for restrictions.
  3. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 12

Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage or DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage

6

Important: : Before continuing with the diagnosis, zero the EVAP Pressure and Vacuum gauges on the J 41413 EVAP pressure/purge diagnostic station, refer to tool operating instructions.

  1. Reconnect all of the EVAP hardware that was previously disconnected.
  2. Connect the J 41413 EVAP pressure/purge diagnostic station to the EVAP service port.
  3. Connect the Vacuum Gauge to engine vacuum.
  4. With the scan tool, command the EVAP vent solenoid on .

    5. Important:: Do not exceed the pressure given in the first specified value.

  5. Pressurize the EVAP system to the first specified value, monitor the pressure using the gauge on the station.
  6. With the scan tool, observe the fuel tank pressure.

Does the fuel tank pressure equal the second specified value?

1.25 kPa

(5 in. H2O)

.96 kPa (3.85 in. H2O)

Go to Step 7

Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage

or

DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage

7
  1. Maintain the EVAP pressure at the first specified value.
  2. With the scan tool, command the EVAP vent solenoid off , while observing the EVAP pressure gauge on the J 41413 EVAP pressure/purge diagnostic station.

Does the EVAP pressure return to the second specified value within 5 seconds?

1.25 kPa (5 in. H2O)

0 kPa (0 in. H2O)

Go to Diagnostic Aids

Go to Step 8

8
  1. Disconnect the AIR vent hose from the EVAP canister.
  2. Switch the rotary switch on the J 41413 EVAP pressure/purge diagnostic station to PURGE.
  3. Start the engine.
  4. Allow the engine to reach the normal operating temperature.
  5. With the scan tool command the EVAP purge solenoid valve on.
  6. Observe the vacuum gauge for 5 seconds while holding the engine speed at 2,500 RPM.

Does the vacuum remain less than the second specified value?

2.49 kPa (10 in. H2O)

Go to Step 9

Go to Step 11

9
  1. Turn off the ignition.
  2. Inspect the EVAP vent hose between the EVAP canister and the EVAP vent solenoid for restrictions.
  3. If a problem is found, repair the as necessary.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

10

    Notice: The EVAP canister may have released carbon particles which caused this part to fail and may cause damage to other components. Check the EVAP canister for loose carbon before returning the vehicle to service.

  1. Replace the EVAP vent solenoid. Refer to Evaporative Emission Vent Valve Replacement .
  2. If carbon particles are found in the component refer to Evaporative Emission System Cleaning .

Did you complete the replacement?

--

Go to Step 12

--

11
  1. Turn off the ignition.

    2. Notice: The EVAP canister may have released carbon particles which caused this part to fail and may cause damage to other components. Check the EVAP canister for loose carbon before returning the vehicle to service.

  2. Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement .
  3. Inspect the EVAP System for carbon particles for the canister, refer to Evaporative Emission System Cleaning .

Did you complete the replacement?

--

Go to Step 12

--

12
  1. Reconnect all the EVAP hardware that was previously disconnected.
  2. Turn on the ignition, with the engine off.
  3. With the scan tool, command the EVAP vent solenoid on.
  4. Pressurize the EVAP system to the first specified value.
  5. Switch the rotary switch on the J 41413 EVAP pressure/purge diagnostic station to HOLD.
  6. With the scan tool, command the EVAP vent solenoid off while observing the J 41413 EVAP pressure gauge on the station.

Does the EVAP pressure return to the second specified value within 5 seconds?

1.25 kPa (5 in. H2O)

0 kPa (0 in. H2O)

Go to Step 13

Go to Step 3

13
  1. Use a scan tool to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 3

System OK