2001 Chevrolet/Geo Camaro  

DTC P0446

System Description

This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path. The control module commands the EVAP canister purge solenoid Open and the EVAP canister vent solenoid Closed. This allows vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the EVAP canister purge solenoid Closed and the EVAP canister vent solenoid Open. The control module monitors the fuel tank pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near 0 inches H2O in a calibrated time, this DTC sets.

The following table illustrates the relationship between the ON and OFF states, and the Open or Closed states of the EVAP canister purge and vent valves.

Control Module Command

EVAP Canister Purge Solenoid

EVAP Canister Vent Solenoid

ON

Open

Closed

OFF

Closed

Open
Conditions for Running the DTC
Action Taken When the DTC Sets
Conditions for Clearing the MIL/DTC
Diagnostic Aids

An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP vent valve inlet or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This test determines if the fuel tank pressure (FTP) sensor is functioning.

Step

Action

Value(s)

Yes

No

Schematic Reference: Evaporative Emissions (EVAP) Hose Routing Diagram

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Did DTC P0443, P0449, P0452, or P0453 set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

Inspect the evaporative emission (EVAP) system for the following conditions:

  • A damaged EVAP vent valve
  • A pinched EVAP fresh air vent hose

Did you find and correct the condition?

--

Go to Step 14

Go to Step 4

4
  1. Disconnect the purge line from the EVAP purge valve.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the fuel tank pressure (FTP) parameter.

Does the scan tool indicate fuel tank pressure near the specified value?

0 in H2O

Go to Step 5

Go to Step 8

5

Important

Always zero the EVAP pressure and vacuum (in H2O) gauges on the J 41413 EVAP Pressure/Purge Diagnostic Station before proceeding with diagnosis.

  1. Turn OFF the ignition.
  2. Reconnect all previously disconnected hardware.
  3. Install the J 41416 Fuel Tank Cap Adaptor.
  4. Connect the J 41413 and the vehicle fuel fill cap to the J 41416 .
  5. Turn ON the ignition, with the engine OFF.
  6. Command the EVAP canister vent valve ON with a scan tool.

    Important

    Do not exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.

  7. With the J 41413 , pressurize the EVAP system to the first specified value.
  8. Rotate the EVAP pressure/purge diagnostic station rotary switch to the OFF/HOLD position.
  9. Command the EVAP canister vent valve OFF with a scan tool.

Does the scan tool indicate fuel tank pressure FTP near the second specified value?

5 in H2O

0 in H2O

Go to Diagnostic Aids

Go to Step 6

6

Disconnect the EVAP canister vent hose from the EVAP canister vent valve.

Does the scan tool indicate that the fuel tank pressure is within the specified range?

-0.5 to +0.5 in H2O

Go to Step 10

Go to Step 7

7

Disconnect the EVAP vent hose from the EVAP canister.

Does the scan tool indicate FTP near the second specified value?

0 in H2O

Go to Step 13

Go to Step 11

8

With a scan tool, observe the FTP sensor voltage.

Is the FTP sensor voltage more than the specified value?

4.3 V

Go to DTC P0453

Go to Step 9

9

Test for poor connections at the harness connector of the FTP sensor. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 12

10

Replace the EVAP canister vent valve. Refer to Evaporative Emission (EVAP) Canister Vent Valve Replacement .

Did you complete the replacement?

--

Go to Step 14

--

11

Replace the EVAP canister. Refer to Evaporative Emission (EVAP) Canister Replacement .

Did you complete the replacement?

--

Go to Step 14

--

12

Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 14

--

13

Repair for a blockage in the EVAP vent hose.

Did you complete the repair?

--

Go to Step 14

--

14
  1. Turn ON the ignition, with the engine OFF.
  2. Command the EVAP canister vent valve ON with a scan tool.

    Important

    Do not exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.

  3. Pressurize the EVAP system to the specified value with the J 41413 .
  4. Place the control knob on the J 41413 to the OFF/HOLD position.
  5. Monitor the J 41413 pressure gage.
  6. Command the EVAP canister vent valve OFF.

Does the EVAP system pressure decrease?

--

Go to Step 15

Go to Step 3

15

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK