For 1990-2009 cars
Engine Controls Components
Engine Data Sensors, MAF, EVAP Switch, EVAP Valve, EGR
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The evaporative system includes the following components:

• | The fuel tank.

• | The EVAP canister vent valve.

• | The fuel tank pressure sensor.

• | The fuel pipes and hoses.

• | The fuel cap.

• | The EVAP vapor lines.

• | Ther EVAP purge lines.

• | The evaporative emission canister.

• | The EVAP purge valve.

A restricted or blocked EVAP canister vent path is detected by monitoring fuel tank pressure during normal operation (EVAP canister vent valve open, EVAP purge valve normal). With the EVAP canister vent valve open, vacuum level in the system should be very low unless the vent path is blocked. A blockage can be caused by the following conditions:

• | Malfunctioning EVAP canister vent valve (stuck closed).

• | Plugged kinked or pinched EVAP canister vent hose.

• | Shorted EVAP canister vent valve control circuit.

• | Plugged evaporative canister.

An incorrect fuel tank pressure sensor signal is detected by monitoring fuel tank pressure when the key is first turned ON during a cold start. If the fuel tank pressure signal is out of range, the EVAP diagnostic will not be able to detect leaks.

If any of the conditions described above are present, DTC P0446 will set.

### Conditions for Running the DTC

• | No VSS, TP sensor, HO2S, Misfire, IAT, MAP, Fuel Trim, Injector Circuit, EGR Pintle Position, ECT, IAT, or MAF sensor DTCs set.

• | Fuel tank level is between 15% and 85%.

• | BARO is greater than 75 kPa.

• | System voltage is between 8 and 16 volts.

### Conditions for Setting the DTC

• | Fuel tank pressure is greater than 10 in. H2O.

• | The above conditions are present for up to 4 seconds.

### Action Taken When the DTC Sets

Important: Although these diagnostics are considered type A, they act like type B diagnostics under certain conditions. Whenever the EVAP diagnostics report that the system has passed, or if the battery has been disconnected, the diagnostic must fail during two consecutive cold start trips before setting a DTC. The initial failure is not reported to the diagnostic executive or displayed on a scan tool. A passing system always reports to the diagnostic executive immediately.

• | The PCM will illuminate the MIL during the first trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.

• | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

### 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 canister vent valve 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 canister vent valve is not restricted.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused 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:

1. If a EVAP canister vent valve 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.

2. Checks the fuel tank pressure sensor at ambient pressure.

3. Verifies that the fuel tank pressure sensor reacts to EVAP system pressure changes.

4. Checks for a blocked EVAP canister.

#### DTC P0446 - EVAP Canister Vent Blocked

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain OBD System Check performed? | -- | Go to Step 2 | Go to the Powertrain On Board Diagnostic (OBD) System Check
2 | Is DTC P1676 also set? | -- | Go to DTC P1676 Evaporative Emission (EVAP) Purge Solenoid Control Circuit | Go to Step 3
3 |

1. Turn on the ignition switch.
2. Capture Fail Record data for DTC P0446 and clear DTCs.
3. Turn OFF the ignition switch.
4. Remove the fuel cap.
5. Turn on the ignition switch.
6. Observe Fuel Tank Pressure on the scan tool.

Is Fuel Tank Pressure at the specified value?

0 in. H2O

Go to Step 4

Go to DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage

4 | Important: : Before continuing with diagnosis, zero the EVAP Pressure and Vacuum (inches of H2O) gauges on the

(1) | Main Valve
(2) | Evaporative Emission System Purge/Presure Diagnostic Station J 41413
(3) | Nitrogen Cylinder
(4) | Black Connecting Hose
(5) | Threaded Fitting
(6) | Gauge Set

EVAP pressure/purge diagnostic station (refer to tool operating instructions).

1. Replace the fuel cap.
2. Using the scan tool, command the EVAP canister vent valve on (Closed).
3. Connect the

   (1) | Main Valve
   (2) | Evaporative Emission System Purge/Presure Diagnostic Station J 41413
   (3) | Nitrogen Cylinder
   (4) | Black Connecting Hose
   (5) | Threaded Fitting
   (6) | Gauge Set

   EVAP pressure/purge diagnostic station to the EVAP service port.
4. Pressurize the EVAP system to the specified value using the

   (1) | Main Valve
   (2) | Evaporative Emission System Purge/Presure Diagnostic Station J 41413
   (3) | Nitrogen Cylinder
   (4) | Black Connecting Hose
   (5) | Threaded Fitting
   (6) | Gauge Set

   EVAP pressure/purge diagnostic station (monitor pressure using the EVAP pressure gauge on the

   (1) | Main Valve
   (2) | Evaporative Emission System Purge/Presure Diagnostic Station J 41413
   (3) | Nitrogen Cylinder
   (4) | Black Connecting Hose
   (5) | Threaded Fitting
   (6) | Gauge Set

   EVAP pressure/purge diagnostic station).
5. Observe Fuel Tank Pressure on the scan tool.

Is Fuel Tank Pressure at the specified value?

5 in. H2O

Go to Step 5

Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage

5 |

1. Maintain EVAP pressure at the first specified value.
2. Using the scan tool, command the EVAP canister vent valve OFF (Open) while observing the EVAP pressure gauge on the EVAP pressure/purge diagnostic station.

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

5 in. H2O

0 in. H2O

Go to Diagnostic Aids

Go to Step 6

6 |

1. Disconnect the large vent hose (marked AIR ) from the EVAP canister.
2. Switch the rotary switch on the EVAP pressure/purge diagnostic station to PURGE.
3. Start the vehicle and allow to reach operating temperature
4. Using the scan tool, command the EVAP purge valve on (open).
5. Monitor the Vacuum (inches H2O) gauge on the EVAP pressure/purge diagnostic station for 5 seconds while holding the engine speed at 2500 RPM.

Does the vacuum remain less than the specified value?

-45 in. H2O

Go to Step 7

Go to Step 9

7 |

1. Inspect the vent hose between the EVAP canister and the EVAP vent solenoid for being kinked, pinched, or otherwise blocked.
2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 10

Go to Step 8

8 | Replace the EVAP canister vent valve. Refer to Evaporative Emission Vent Valve Replacement . Is the action complete? | -- | Go to Step 10 | --
9 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Is the action complete? | -- | Go to Step 10 | --
10 |

1. Using the scan tool, command the EVAP canister vent valve on (Closed).
2. Pressurize the EVAP system to the first specified value.
3. Switch the rotary switch on the EVAP pressure/purge diagnostic station to HOLD.
4. Using the scan tool, command the EVAP canister vent valve OFF (Open) while observing the EVAP pressure gauge on the EVAP pressure/purge diagnostic station.

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

5 in. H2O

0 in. H2O

System OK

Go to Step 3