Diagnostic Aids

WARNING: This page is about a different car, the 2007 Hummer H2. However, it is still accessible from the selected car via links, so may be relevant.

When using the Evaporative 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 inches H2O. More than 5 inches 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 Testing for Intermittent Conditions and Poor Connections .
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.

DTC P0446

Step	Action	Values	Yes	No
Schematic Reference: Evaporative Emissions Hose Routing Diagram
1	Did you perform the Diagnostic System Check - Vehicle?	-	Go to Step 2	Go to Diagnostic System Check - Vehicle
2	Inspect the Evaporative Emission (EVAP) System for the following conditions: A damaged EVAP canister vent solenoid valve-Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . A pinched EVAP vent hose A damaged EVAP canister-Refer to Evaporative Emission Canister Replacement . Did you find and correct the condition?	-	Go to Step 15	Go to Step 3
3	Turn OFF the ignition. Remove the fuel filler cap. Turn ON the ignition, with the engine OFF. Is the fuel tank pressure sensor parameter within the specified range?	-1 to +1 in H2O	Go to Step 4	Go to Step 9
4	Turn OFF the ignition. Connect the J 41413-200 Evaporative Emission System Tester (EEST) power supply clips to a known good 12-volt source. See Special Tools . Install the J 41415-40 Fuel Tank Cap Adapter or GE-41415-50 Fuel Tank Cap Adapter to the fuel fill pipe. See Special Tools . Connect the fuel fill cap to the J 41415-40 or to GE-41415-50 . See Special Tools . Connect the J 41413-200 nitrogen/smoke supply hose to J 41415-40 or to GE-41415-50 . See Special Tools . Turn ON the ignition, with the engine OFF. Command the EVAP canister vent solenoid valve closed with a scan tool. Turn the nitrogen/smoke valve on the J 41413-200 control panel to NITROGEN. See Special Tools . IMPORTANT: DO NOT exceed the specified value in this step. Exceeding the specified value may cause the EVAP canister vent solenoid valve to remain closed, or produce incorrect test results. Use the remote switch to pressurize the EVAP system to the first specified value. Observe the fuel tank pressure sensor in H2O with a scan tool. Command the EVAP canister vent solenoid valve open with a scan tool. Is the fuel tank pressure sensor parameter less than the second specified value?	5 in H2O 1 in H2O	Go to Step 5	Go to Step 7
5	Connect the J 41413-200 nitrogen/smoke supply hose and the vehicle fuel fill cap to the J 41415-40 or GE-41415-50 . See Special Tools . Start the engine. Allow the engine to idle. Use the purge/seal function to seal the system with a scan tool. Command the EVAP canister purge solenoid valve to 20 percent. Observe the vacuum/pressure gage of the J 41413-200 and the FTP parameter on the scan tool. See Special Tools . Allow the vacuum to increase on the gage of the J 41413-200 until it reaches approximately 16 inches H2O. See Special Tools . Did the pressure reading on the J 41413-200 gage agree with the scan tool FTP parameter until the vacuum reached the abort limit on the scan tool?. See Special Tools .	-	Go to Step 6	Go to Step 9
6	Did the FTP parameter on a scan tool display more than the specified value?	3.2 V	Go to Diagnostic Aids	Go to Step 12
7	Disconnect the EVAP vent hose from the EVAP canister vent solenoid valve. Is the fuel tank pressure sensor parameter less than the specified value?	1 in H2O	Go to Step 13	Go to Step 8
8	Disconnect the EVAP vent hose from the EVAP canister. Is the fuel tank pressure sensor parameter less than the specified value?	1 in H2O	Go to Step 11	Go to Step 14
9	Test for an intermittent and for a poor connection at the fuel tank pressure (FTP) sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition?	-	Go to Step 15	Go to Step 10
10	Test the low reference circuit of the FTP sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition?	-	Go to Step 15	Go to Step 12
11	Repair the pinched or restricted EVAP vent hose. Did you complete the repair?	-	Go to Step 15	-
12	Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement?	-	Go to Step 15	-
13	Replace the EVAP canister vent solenoid valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement . Did you complete the replacement?	-	Go to Step 15	-
14	Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Did you complete the replacement?	-	Go to Step 15	-
15	Turn OFF the ignition. Remove the fuel filler cap. Turn ON the ignition, with the engine OFF. Is the fuel tank pressure sensor parameter within the specified range?	-1 to +1 in H2O	Go to Step 16	Go to Step 2
16	IMPORTANT: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results. Turn OFF the ignition. Reconnect all disconnected components. Connect J 41413-200 to the fuel fill pipe. See Special Tools . Turn ON the ignition, with the engine OFF. Command the EVAP canister vent solenoid valve closed with a scan tool. Turn the nitrogen/smoke valve on the J 41413-200 control panel to NITROGEN. See Special Tools . Use the remote switch to pressurize the EVAP system to the first specified value. Observe the fuel tank pressure sensor in H2O with a scan tool. Command the EVAP canister vent solenoid valve open with a scan tool. Is the fuel tank pressure sensor parameter less than the second specified value?	5 in H2O 1 in H2O	Go to Step 17	Go to Step 2
17	Observe the Capture Info with a scan tool. Have any other DTCs not been diagnosed?	-	Go to Diagnostic Trouble Code (DTC) List - Vehicle	System OK