DTC P0446. Chevrolet Tahoe

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2001 🢒 Tahoe - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 DTC P0446

Circuit Description

The powertrain control module (PCM) monitors the performance of the evaporative emission (EVAP) system by applying a predetermined level of vacuum to the EVAP system then monitors the vacuum decay rate. The PCM sets this diagnostic trouble code (DTC) if the vacuum decay rate is more than a predetermined value.

Conditions for Running the DTC

•	DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0443, P0449, P0452, P0453, P1111, P1112, P1114, P1115, P1121 or P1122 are not set.

•	The ignition voltage is between 10-18 volts.

•	The barometric pressure is more than 75 kPa.

•	The fuel level is between 15-85 percent of full capacity.

•	The engine coolant temperature (ECT) is between 4-30°C (39-86°F).

•	The intake air temperature is between 4-30°C (39-86°F).

•	The start up engine coolant temperature and the intake air temperature are within 9°C (16°F) of each other.

Conditions for Setting the DTC

•	The EVAP vacuum decay rate is more than a predetermined value.

•	The conditions are present for more than 2 seconds.

•	The vacuum present in the EVAP system is more than a predetermined value.

•	The conditions are present for more 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 control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

•	The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

•	The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

•	A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

•	A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Important:

•	Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

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

•	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.

•	Inspect for charcoal release from the vapor canister. Refer to the Evaporative Emission System Cleaning procedure.

Conditions for Running the Service Bay Test

•	The battery voltage is between 10.5-17.5 volts.

•	The fuel level is between 15 percent and 85 percent of the full capacity.

•	The engine temperature is between 3.5-35°C (38-95°F).

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 malfunctioning or damaged vapor canister

•	Inspect for charcoal release from the vapor canister. Refer to the Evaporative Emission System Cleaning procedure.

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

in H2O	in Hg.	psi
1 in 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.

Tests the fuel tank pressure.

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

Tests the vapor canister and the EVAP vent valve for restriction.

A fuel tank pressure sensor that does not correctly respond to pressure, or vacuum, causes this DTC to set.

Step

Action

Values

Yes

Schematic Reference: Emission Hose Routing Diagram and Engine Controls Schematics

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

Turn OFF the ignition.
Remove the fuel tank cap.
Turn ON the ignition, with the engine OFF.

Important: An open in the fuel tank pressure sensor ground circuit causes the voltage to go high. An open ground circuit may cause DTC P0446 to set, because the PCM senses a fuel tank pressure sensor voltage that is stuck in range, which indicates a restricted EVAP system.

An intermittent leak or restriction is indicated if the vehicle passes the Service Bay Test.

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

Monitor the fuel tank pressure using a scan tool. If another DTC sets, refer to the appropriate DTC table for further diagnosis.

Is the fuel tank pressure near the specified value?

0 in Hg

Go to Step 3

Go to DTC P0453

Inspect the EVAP system for the following conditions:

•	Improperly routed, kinked, or damaged EVAP purge and tank vent lines

•	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 13

Go to Step 4

Important: Ensure that the Conditions for Running the Service Bay Test 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 5

Important: The DTCs must be cleared from the PCM in order to use the output control function on the scan tool.

Clear the DTCs using a scan tool.
Turn OFF the ignition.
Disconnect the fuel tank vapor and the EVAP purge lines from the EVAP vapor canister.
Plug the canister port for the fuel tank vapor line using an appropriate plug.
Connect the J 23738-A hand-held vacuum pump to the EVAP purge line canister fitting.
Turn ON the ignition, with the engine OFF.

Important: If an audible solenoid click cannot be heard and DTC P0449 is not set, inspect the EVAP canister vent solenoid circuits for high resistance.

Command the EVAP vent valve ON, or closed, using the scan tool.
Attempt to apply and hold the specified amount of vacuum using the hand-held vacuum pump.
Command the EVAP vent valve OFF, or 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 8

Go to Step 6

Leave the system as connected in step 5.
Disconnect the vent line at the EVAP vent valve.
Plug the vent line using an appropriate plug.
Attempt to apply and hold the specified amount of vacuum using the hand-held vacuum pump.
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 10

Go to Step 7

Inspect the EVAP vent line from the canister to the EVAP vent valve for restrictions.
Repair as necessary if you find a condition.

Did you find and correct the condition?

Go to Step 13

Go to Step 11

Inspect the fuel tank vapor line for a restriction.
Repair condition, as necessary.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

Turn OFF the ignition.
Remove the plug and the hand-held vacuum pump.
Reconnect the EVAP vapor canister purge and vent lines.

Important: Always zero the EVAP pressure and vacuum (in H2O) gauges on the EVAP pressure and purge diagnostic station before proceeding with diagnosis.

Connect the J 41413 EVAP pressure and purge diagnostic station to the EVAP system service port.
Turn ON the ignition, with the engine OFF.
Seal the EVAP system with the scan tool.
Pressurize the EVAP system with the EVAP pressure and purge diagnostic station.
Allow the system pressure to stabilize, on the scan tool, and then rotate the J 41413 EVAP diagnostic station selector to the OFF or HOLD position.

Important: The fuel tank pressure sensor range is from +7.5 in. H2O of pressure to -17.5 in. H2O of pressure or vacuum. In order to test the fuel tank pressure sensor for vacuum response, command the EVAP purge solenoid valve ON with the engine running and quickly SEAL the system using the scan tool. Leaving the EVAP purge solenoid valve ON for a longer period of time allows a greater level of vacuum to develop.

Compare the pressure gauge (in H2O) on the EVAP pressure and purge diagnostic station to the fuel tank pressure shown on the scan tool.

Does the fuel tank pressure sensor indicate the actual amount of pressure in the EVAP system?

Go to Step 4

Go to Step 12

Replace the EVAP vent valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement .

Is the action complete?

Go to Step 13

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

Is the action complete?

Go to Step 13

Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement .

Is the action complete?

Go to Step 13

Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 14

Go to Step 2

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