PO446 Please Help!!!!
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Junior Member
Joined: Oct 2017
Posts: 9
PO446 Please Help!!!!
My H3 has been in the shop now multiple times for a PO446 code.In the past it has also given PO445 & PO455. I have Changed the purge valve, vapor canister vent selonoid. Sent it back to the shop they then said it had a clogged line going from the Gas tank to the evap canister so all that was replace. Brought it home and within 24 miles the check engine light went off again. Brought it back they dropped the tank down thinking they crimped the line when putting it back together. They drove it for awhile and gave it a clean bill of health again. I drove our daughter back to Albany from Rochester ny. Put another 200+ on it and again the check engine light went off again. I have changed everything out on this and can not figure it out. I have paid shops to figure it out and they have not been very successful. Everything from a new gas cap to the steering rack. Everything is new, do you have any suggestions. I know the steering rack isn’t relevant I was just making a point. I changed the engine out with a new one and in that process I started replacing everything, steering rack was bad. I’m lost on this everything pertaining to emissions has been replaced as well. Please help me if you can, if you can’t and I give up what would a fair price be if I sold this. Thank you
Last edited by Deano; Dec 30, 2020 at 10:52 PM.
Senior Member
Joined: Jul 2012
Posts: 8,999
From: C-Town
Hi Jeff, I hope you enjoyed your holiday. I wasn’t sure where to post this question so I thought I would message you, I am sorry if this was wrong to do. My H3 has been in the shop now multiple times for a PO446 code.In the past it has also given PO445 & PO455. I have Changed the purge valve, vapor canister vent selonoid. Sent it back to the shop they then said it had a clogged line going from the Gas tank to the evap canister so all that was replace. Brought it home and within 24 miles the check engine light went off again. Brought it back they dropped the tank down thinking they crimped the line when putting it back together. They drove it for awhile and gave it a clean bill of health again. I drove our daughter back to Albany from Rochester ny. Put another 200+ on it and again the check engine light went off again. I have changed everything out on this and can not figure it out. I have paid shops to figure it out and they have not been very successful. Everything from a new gas cap to the steering rack. Everything is new, do you have any suggestions. I know the steering rack isn’t relevant I was just making a point. I changed the engine out with a new one and in that process I started replacing everything, steering rack was bad. I’m lost on this everything pertaining to emissions has been replaced as well. Please help me if you can, if you can’t and I give up what would a fair price be if I sold this. Thank you
Super Moderator
Joined: Jul 2007
Posts: 13,090
From: Boat Town USA MI
Me. I asked him to post it out in the forums after a PM exchange.
I think the shop(s) he took it to for diagnosis never bothered, they just threw parts at the code. A P0446 is not a code that points to a specific problem, rather it indicates a voltage irregularity in the EVAP vent control circuit. It could be many different things, hence all the work/parts thrown at it. IMHO a P0446 in a late model GM points to the simple vent valve solenoid in most cases, but definitely not all. Deano already had the vent valve replaced, or that is what the shop told him they did.
I think the shop(s) he took it to for diagnosis never bothered, they just threw parts at the code. A P0446 is not a code that points to a specific problem, rather it indicates a voltage irregularity in the EVAP vent control circuit. It could be many different things, hence all the work/parts thrown at it. IMHO a P0446 in a late model GM points to the simple vent valve solenoid in most cases, but definitely not all. Deano already had the vent valve replaced, or that is what the shop told him they did.
Super Moderator
Joined: Jul 2007
Posts: 13,090
From: Boat Town USA MI
With as much as has been thrown at Deano's 3, I think a scan is going to be needed, but and inspection of the EVAP hoses for cracks or holes is a good idea.
We have no scan info other than past codes. A guess would be the fuel tank pressure sensor.
We have no scan info other than past codes. A guess would be the fuel tank pressure sensor.
Super Moderator
Joined: Jul 2007
Posts: 13,090
From: Boat Town USA MI
Here is the list of things that need to be ran down.
What can cause the code P0446:
- faulty vent control valve
- blockage at the vent hose, vent filter or vent control valve
- open or short in the vent control valve circuit
- bad charcoal canister
- EVAP system leak
- faulty EVAP system pressure sensor
- bad vacuum switching valve (VSV) (Toyota, Lexus)
- stuck open purge valve (solenoid)
Add a bad PCM or fault in the PCM wire to the vent control circuit.
What can cause the code P0446:
- faulty vent control valve
- blockage at the vent hose, vent filter or vent control valve
- open or short in the vent control valve circuit
- bad charcoal canister
- EVAP system leak
- faulty EVAP system pressure sensor
- bad vacuum switching valve (VSV) (Toyota, Lexus)
- stuck open purge valve (solenoid)
Add a bad PCM or fault in the PCM wire to the vent control circuit.
Senior Member
Joined: Jul 2012
Posts: 8,999
From: C-Town
DTC P0446
System Description
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 following 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.
Control Module Command
EVAP Canister Purge Solenoid Valve
EVAP Canister Vent Solenoid Valve
ON
Open
Closed
OFF
Closed
Open
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0446 Evaporative Emissions (EVAP) Vent System Performance
Conditions for Running the DTC
• DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0125, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0442, P0443, P0449, P0452, P0453, P0455, P0502, P0503, P1111, P1112, P1114, P1115, P1120 are not set.
• The ignition voltage is between 10-18 volts.
• The barometric pressure (BARO) is more 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 continuously once the above conditions are met.
Conditions for Setting the DTC
The FTP is not within a calibrated amount for a calibrated period of time.
Action Taken When the DTC Sets
• 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.
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
• 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.
• 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 .
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 in Vehicle DTC Information
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 12
Go to Step 3
3
Turn OFF the ignition.
Disconnect the purge pipe at the EVAP service port.
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 8
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 line.
Connect the J 41413-200 Evaporative Emissions System Tester (EEST) power supply clips to a known good 12-volt source.
Install the GE-41415-50 Interrupted Thread Fuel Tank Cap Adapter to the fuel fill pipe.
Connect the fuel fill cap to the GE-41415-50 .
Connect the J 41413-200 nitrogen/smoke supply hose to the GE-41415-50 .
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.
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 Diagnostic Aids
Go to Step 5
5
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 10
Go to Step 6
6
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 7
Go to Step 11
7
Repair the pinched or restricted EVAP vent hose.
Did you complete the repair?
--
Go to Step 12
--
8
Test for poor connections at the harness connector of the fuel tank pressure (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 12
Go to Step 9
9
Replace the FTP sensor. Refer to Fuel Tank Replacement .
Did you complete the replacement?
--
Go to Step 12
--
10
Replace the EVAP vent solenoid valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement .
Did you complete the replacement?
--
Go to Step 12
--
11
Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement .
Did you complete the replacement?
--
Go to Step 12
--
12
Turn OFF the ignition.
Disconnect the purge line from the EVAP canister purge solenoid valve. Refer to Evaporative Emission 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 13
Go to Step 2
13
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 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.
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 14
Go to Step 2
14
Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?
--
Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information
System OK
System Description
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 following 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.
Control Module Command
EVAP Canister Purge Solenoid Valve
EVAP Canister Vent Solenoid Valve
ON
Open
Closed
OFF
Closed
Open
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0446 Evaporative Emissions (EVAP) Vent System Performance
Conditions for Running the DTC
• DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0125, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0442, P0443, P0449, P0452, P0453, P0455, P0502, P0503, P1111, P1112, P1114, P1115, P1120 are not set.
• The ignition voltage is between 10-18 volts.
• The barometric pressure (BARO) is more 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 continuously once the above conditions are met.
Conditions for Setting the DTC
The FTP is not within a calibrated amount for a calibrated period of time.
Action Taken When the DTC Sets
• 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.
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
• 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.
• 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 .
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 in Vehicle DTC Information
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 12
Go to Step 3
3
Turn OFF the ignition.
Disconnect the purge pipe at the EVAP service port.
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 8
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 line.
Connect the J 41413-200 Evaporative Emissions System Tester (EEST) power supply clips to a known good 12-volt source.
Install the GE-41415-50 Interrupted Thread Fuel Tank Cap Adapter to the fuel fill pipe.
Connect the fuel fill cap to the GE-41415-50 .
Connect the J 41413-200 nitrogen/smoke supply hose to the GE-41415-50 .
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.
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 Diagnostic Aids
Go to Step 5
5
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 10
Go to Step 6
6
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 7
Go to Step 11
7
Repair the pinched or restricted EVAP vent hose.
Did you complete the repair?
--
Go to Step 12
--
8
Test for poor connections at the harness connector of the fuel tank pressure (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 12
Go to Step 9
9
Replace the FTP sensor. Refer to Fuel Tank Replacement .
Did you complete the replacement?
--
Go to Step 12
--
10
Replace the EVAP vent solenoid valve. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement .
Did you complete the replacement?
--
Go to Step 12
--
11
Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement .
Did you complete the replacement?
--
Go to Step 12
--
12
Turn OFF the ignition.
Disconnect the purge line from the EVAP canister purge solenoid valve. Refer to Evaporative Emission 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 13
Go to Step 2
13
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 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.
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 14
Go to Step 2
14
Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?
--
Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information
System OK