DTC P0446 Evaporative Emission (EVAP) Vent System Performance


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Circuit Description

The PCM monitors the performance of the EVAP system by applying a predetermined level of vacuum to the EVAP system then monitors the vacuum decay rate. The PCM sets this DTC if the vacuum decay rate is greater than a predetermined value.

Conditions for Running the DTC

  • DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0420, P0430, P0452, P0453, P0500, P0502, P0503, P1111, P1112, P1114, P1115 or HO2S DTCs are not set.
  • The ignition voltage is between 10 and 17 volts.
  • The barometric pressure is more than 75 kPa.
  • The fuel level is between 15% and 85% of full capacity.
  • The engine coolant temperature is between 4C (39F) and 30C (86F).
  • The intake air temperature is between 4C (39F) and 30C (86F).
  • The start up engine coolant temperature and the intake air temperature are within 9C (16F) of each other.

Conditions for Setting the DTC

  • The EVAP vacuum decay rate is greater than a predetermined value.
  • The conditions are present for greater than 2 seconds.

OR

  • The vacuum present in the EVAP system is greater than a predetermined value.
  • The conditions are present for greater than 4 seconds.

Important

This DTC does not report a first failed test. A first fail of this DTC will have a scan tool status as Not Run.

Action Taken When the DTC Sets

  • The PCM will illuminate the Malfunction Indicator Lamp (MIL) after two consecutive drive trips that the diagnostic runs and fails.
  • The PCM will record operating conditions at the time the DTC sets. This information will be stored in the Freeze Frame and Failure Records.
  • A first failure of this DTC will NOT store in Last Test Failed or History.

Conditions for Clearing the MIL/DTC

  • The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
  • A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
  • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
  • Use a scan tool in order to clear the MIL and the DTC.

Diagnostic Aids

Important

An accurate indication of fuel level is required for the PCM to properly Pass or Fail this DTC. Always diagnose the fuel level sensor DTC's before performing this DTC's diagnostic table. Always inspect for fuel level sensor DTC's stored as History.

Important

The Service Bay Test may have to be performed in cold ambient air temperatures when the vehicle is running a winter grade fuel. The scan tool displays a message when the service bay test does not run.

Conditions for Running the Service Bay Test

  • The battery voltage is between 10.5 and 17.5 volts.
  • The fuel level is between 15% and 85% of the full capacity.
  • The engine temperature is between 3.5C (38F) and 35C (95F).

Perform a physical inspection of the EVAP system. Inspect for the following conditions:

  • A loose, missing, defective, or incorrect fuel tank cap
  • Incorrectly routed or defective EVAP system vacuum and vapor lines
  • A stuck closed EVAP Vent Valve
  • A restricted or blocked EVAP system hose
  • A restricted or stuck closed fuel tank rollover valves
  • A malfunctioning or damaged vapor canister

Inspect for charcoal release from the vapor canister. Refer to the EVAP System Cleaning procedure.

The vacuum and pressure in the EVAP system is measured in inches of water (H2O). Most gauges measure vacuum in inches of mercury (Hg) and pressure in pounds per square inch (psi). The following shows how the values compare:

in H2O

in Hg

psi

1in H2O

0.07 in Hg

0.0361 psi

5 in H2O

0.36 in Hg

0.180 psi

10 in H2O

0.73 in Hg

0.361 psi

15 in H2O

1.10 in Hg

0.541 psi

Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

  1. An intermittent leak or restriction is indicated if the vehicle passes the Service Bay Test. A fuel tank cap that is loose or off causes this DTC to set.

If the Service Bay Test can not be run, proceed to Step 5. If a fault is not currently present the diagnostic table steps will return you to Step 3.

  1. Testing the vapor canister and the EVAP Vent Valve for restriction.
  1. A Fuel Tank Pressure sensor that does not correctly respond to pressure (or vacuum) causes this DTC to set.

An open fuel tank pressure sensor ground circuit causes this DTC to set. If the fuel tank pressure sensor does not respond to pressure (or vacuum), inspect the ground circuit for an open.

The Fuel Tank Pressure sensor monitors a range from 7.5 in. H2O of pressure to -17.5 in. H2O of pressure (vacuum).

In order to test the Fuel Tank Pressure sensor for vacuum response, command the EVAP Purge Solenoid Valve to 100 percent with the engine running and quickly SEAL the system. Leaving the EVAP Purge Solenoid Valve activated for a longer period of time allows a greater level of vacuum to develop.

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to A Powertrain On Board Diagnostic (OBD) System Check

2

Inspect the EVAP system for the following conditions:

  1. Improperly routed, kinked or damaged EVAP purge and tank vent lines.
  2. A damaged EVAP system component.

Repair the EVAP system as necessary if you find a condition. Did you find and correct the condition?

--

Go to Step 12

Go to Step 3

3

Important

Ensure that The Conditions for Running the Service Bay are met before proceeding with this diagnostic. Refer to Diagnostic Aids.

Perform the EVAP system Service Bay Test.

Does the vehicle pass the Service Bay Test?

--

Go to Diagnostic Aids

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the fuel tank vapor and the EVAP purge lines from the EVAP vapor canister. Refer to EVAP Canister Replacement .
  3. Plug the CANISTER fitting for the fuel tank vapor line.
  4. Connect the hand held vacuum pump J 23738-A to the EVAP purge line canister fitting.
  5. Turn ON the ignition leaving the engine OFF.
  6. Command the EVAP Vent Valve ON (closed) using the scan tool.
  7. Attempt to apply and hold the specified amount of vacuum using the hand held vacuum pump.
  8. Command the EVAP Vent Valve OFF (open) while monitoring the hand held vacuum pump gauge.

Does the vacuum drop from the specified value when the EVAP Vent Valve is opened?

5 in. Hg.

Go to Step 7

Go to Step 5

5

  1. Leave the system as connected in Step 4.
  2. Disconnect the vent line at the EVAP Vent Valve.
  3. Plug the vent line.
  4. Attempt to apply and hold the specified amount of vacuum using the hand held vacuum pump J 23738-A .
  5. Remove the plug from the vent line while monitoring the hand held vacuum pump gauge.

Does the vacuum drop from the specified value when the vent line is unplugged?

5 in. Hg.

Go to Step 9

Go to Step 6

6

  1. Inspect the EVAP Vent line from the canister to the EVAP Vent Valve for restrictions.
  2. Repair as necessary if you find a condition.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

7

  1. Inspect the fuel tank vapor line for a restriction.
  2. Repair as necessary if you find a condition.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 8

8

Important

The following steps require the EVAP pressure/purge diagnostic station J 41413 .

Always zero the EVAP Pressure and Vacuum (in. H2O) gauges on the EVAP pressure/purge diagnostic station before proceeding with diagnosis.

  1. Turn OFF the ignition.
  2. Remove the plug and the hand held vacuum pump.
  3. Reconnect the EVAP vapor canister purge and vent lines.
  4. Connect the EVAP pressure/purge diagnostic station to the EVAP system service port.
  5. Operate the vehicle until the EVAP Purge Solenoid Valve can be commanded to a percentage with a scan tool.
  6. Command the EVAP Purge Solenoid Valve to 100 percent with the engine running and quickly SEAL the system with the scan tool.
  7. Compare the EVAP pressure/purge diagnostic station's vacuum gauge (in. H2O) to the vacuum shown on the scan tool from the Fuel Tank Pressure sensor while the system is sealed.

Does the Fuel Tank Pressure sensor indicate the actual amount of vacuum in the EVAP system?

--

Go to Step 3

Go to Step 11

9

Replace the EVAP Vent Valve. Refer to EVAP Vent Valve Replacement . Is the action complete?

--

Go to Step 13

--

10

Replace the EVAP Vapor Canister. Refer to EVAP Canister Replacement . Is the action complete?

--

Go to Step 13

--

11

Replace the Fuel Tank Pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete?

--

Go to Step 13

--

12

  1. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool.
  2. Idle the engine at the normal operating temperature.
  3. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test ran and passed?

--

Go to Step 13

Go to Step 2

13

Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed?

--

Go to the applicable DTC

System OK