Diagnostic Aids

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP vent solenoid valve inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill condition.
An EVAP canister, vent hose, or vent solenoid valve that has restricted flow may cause this DTC to set. Using 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.
For intermittent conditions, refer to Intermittent Conditions .

DTC P0446

Step	Action	Values	Yes	No
Schematic Reference: Evaporative Emissions (EVAP) Hose Routing Diagram Connector End View Reference: Powertrain Control Module (PCM) Connector End Views or Engine Controls Connector End Views
1	Did you perform the Diagnostic System Check-Engine Controls?	-	Go to Step 2	Go to Diagnostic System Check - Engine Controls
2	Inspect the Evaporative Emission (EVAP) System for the following conditions: A damaged EVAP canister vent solenoid valve-Refer to Evaporative Emission (EVAP) Canister Vent Solenoid Valve Replacement (Pickup) or Evaporative Emission (EVAP) Canister Vent Solenoid Valve Replacement (Cab/Chassis) . A pinched EVAP vent hose A damaged EVAP canister-Refer to Evaporative Emission (EVAP) Canister Replacement (Pickup) or Evaporative Emission (EVAP) Canister Replacement (Cab/Chassis) . Did you find and correct the condition?	-	Go to Step 15	Go to Step 3
3	Turn OFF the ignition. Disconnect the purge line from the EVAP canister purge solenoid valve. Refer to Evaporative Emission (EVAP) Canister Purge Solenoid Valve Replacement . 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	IMPORTANT: DO NOT exceed the specified value in this step. Exceeding the specified value may produce incorrect test results. Turn OFF the ignition. Connect the EVAP purge pipe. Connect the J 41413-200 Evaporative Emissions System Tester (EEST) power supply clips to a known good 12-volt source. Install the J 41415-40 Fuel Tank Cap Adapter to the fuel fill pipe. Connect the fuel fill cap to the J 41415-40 . Connect the J 41413-200 nitrogen/smoke supply hose to the J 41415-40 . 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. Pressurize the EVAP system to the first specified value with the remote switch. Observe the fuel tank pressure (FTP) sensor in H2O with a scan tool. Command the EVAP 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 nitrogen/smoke hose to the EVAP service port. Remove the J 41415-40 . Install the fuel fill cap to the fuel fill pipe. 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 30 percent. Observe the vacuum/pressure gage on the J 41413-200 and the FTP parameter on the scan tool. Allow the vacuum to increase on the gage of the J 41413-200 , until it reaches approximately 16 inches H2O. Use the purge/seal function to seal the system, with a scan tool. Is the difference between the FTP parameter on a scan tool and the vacuum/pressure gage on the J 41413-200 within the specified value, until the vacuum reached the abort limit on a scan tool?	1 in H2O	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 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 FTP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. 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 for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. 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 (EVAP) Canister Vent Solenoid Valve Replacement (Pickup) or Evaporative Emission (EVAP) Canister Vent Solenoid Valve Replacement (Cab/Chassis) . Did you complete the replacement?	-	Go to Step 15	-
14	Replace the EVAP canister. Refer to Evaporative Emission (EVAP) Canister Replacement (Pickup) or Evaporative Emission (EVAP) Canister Replacement (Cab/Chassis) . Did you complete the replacement?	-	Go to Step 15	-
15	Turn OFF the ignition. Disconnect the purge line from the EVAP canister purge solenoid valve. Refer to Evaporative Emission (EVAP) Canister Purge Solenoid Valve Replacement . 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. Connect all disconnected components. Connect the J 41413-200 to the fuel fill pipe. 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. Pressurize the EVAP system to the first specified value with the remote switch. Observe the FTP 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. Are there any DTCs that have not been diagnosed?	-	Go to Diagnostic Trouble Code (DTC) List	System OK