2006 Sierra 1500; check engine light 446

Scooter Randy

New member
Baffling me. I've changed: TPS, plugs, wires, distributer thingy, evap container, had fuel lines blown clear, coils and ECM. What is left? Even changed out Torque converter -- twice --. Runs OK, but blasted light ................. Any one else solved it? ( 300+K , Amsoil oil since new ).


New member
Mine is a 2005 seirra this may help you I am unable to show you the test procedure chart the web site will not let me copy it.

Your Vehicle: 2005 GMC Truck Sierra 1500 2WD V8-4.8L VIN V

Vehicle » A L L Diagnostic Trouble Codes ( DTC ) » Testing and Inspection » P Code Charts » P0446


DTC P0446

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

This diagnostic procedure supports the following DTC:
DTC P0446 Evaporative Emission (EVAP) Vent System Performance


DTCs P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0156, P0157, P0158, P0160, P0161, P0220, P0442, P0443, P0449, P0451, P0452, P0453, P0454, P0455, P0464, P0502, P0503, P1111, P1112, P1114, P1115, P1121, P1122, P1125, P2135 are not set.
The ignition voltage is between 10-18 volts .
The barometric pressure (BARO) is greater than 75 kPa .
The fuel level is between 15-85 percent .
The engine coolant temperature (ECT) is between 4-30°C (39-86°F) .
The intake air temperature (IAT) is between 4-30°C (39-86°F) .
The start up ECT and IAT are within 9°C (16°F) of each other.
DTC P0446 runs once per cold start when the above conditions are met.
The fuel tank pressure sensor is less than -12 inches H2O.
The above condition is present for more than 5 seconds .
The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
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.
When using the electronic emission system tester (EEST) to apply pressure, you can regulate the amount of pressure by activating the remote switch ON and OFF while observing pressure in the EVAP system using a scan tool. DO NOT use more than 5 in H2O. More than 5 in H2O applied to the EVAP system can cause the canister vent solenoid valve to temporarily remain in the closed position, which could lead to misdiagnosis in this procedure.
An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP canister vent solenoid valve inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem.
For intermittent conditions, refer to Intermittent Conditions. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Initial Inspection and Diagnostic Overview\Diagnostic Strategies\Intermittent Conditions
An EVAP canister, vent hose, or vent solenoid valve that has restricted flow may cause this DTC to set. Using a purge solenoid valve command with a scan tool will allow vacuum to be applied to the system instead of pressure. With the EVAP canister vent solenoid valve open and the EVAP canister purge solenoid valve commanded to 100 percent , vacuum should not increase to more than 9 inches H2O.