P0446 Replaced Purge Sol. And Vent Valve. What Next?

helomechs · January 28, 2008

this started about 9 months after i bought the truck, (bought in jul 03) its an 03 silverado extended cab 4.8L

i got a p0446 evap sys malf. i also noticed my hisssing sound when i open the fuel tank had dissappeared. i know the system vacuums out air during cold start ups 15-85% fuel level etc. and that was probably my hiss right? regardless i ignored the code cause i dont have to smog it anytime soon. well i erased it and it didnt come back for a year. erased it again maybe anothe 6 mo. before it came back. so i did lots of research on this site and concluded i should replaced the purge solenoid and upgrade to the "robust vent valve" since these were the 2 most likely causes judging by several topics on this site. i erased the code and it has yet to come back. but i really expected to hear that hissing noise again and since i dont i am expecting to get that light back again. will somebody clue me in on whats happening? how do i know replacing those two components did anything?? and should i be concerned that my tank no longer hisses? be advised i currently have a loss of injector pressure problem which i am sure is a back check valve on the pump assy. i already replaced the pump assy. once because a wires rubbed through the transfer tube coming from pump top top of unit. so it leaked down all pressure at injectors. currently i just give it a 2 second pause after turning the key to let the pump run before starting. so what do i do next???? how do i test the tank to see if its working, i see an attaching point at the purge solenoid... should i check here for vacuum or something??

helomechs · March 17, 2008

i know the system vacuums out air during cold start ups 15-85% fuel level etc. and that was probably my hiss right?

Not right, the system should not be doing anything when you are at a stop.

EVAP System Operation

The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and EVAP vent solenoid to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge solenoid ON, allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent solenoid OFF, fresh air is drawn through the vent solenoid and the vent line to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge solenoid into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking.

Large Leak Test

This tests for large leaks and blockages in the EVAP system. The control module commands the EVAP vent solenoid ON and commands the EVAP purge solenoid ON, with the engine running, allowing engine vacuum into the EVAP system. The control module monitors the fuel tank pressure (FTP) sensor voltage to verify that the system is able to reach a predetermined level of vacuum within a set amount of time. The control module then commands the EVAP purge solenoid OFF, sealing the system, and monitors the vacuum level for decay. If the control module does not detect that the predetermined vacuum level was achieved, or the vacuum decay rate is more than a calibrated level on 2 consecutive tests, DTC P0455 will set.

Small Leak Test

The engine off natural vacuum (EONV) diagnostic is the small-leak detection diagnostic for the EVAP system. While previous leak detection methods were performed with the engine running, the EONV diagnostic monitors the EVAP system pressure or vacuum with the key OFF. Because of this, it may be normal for the control module to remain active for up to 40 minutes after the engine is turned OFF. This is important to remember when performing a parasitic draw test on vehicles equipped with EONV.

The EONV utilizes the temperature changes in the fuel tank immediately following a drive cycle to use the naturally occurring vacuum or pressure in the fuel tank. When the vehicle is driven, the temperature rises in the tank. After the vehicle is parked, the temperature in the tank continues to rise for a period of time, then start to drop. The EONV diagnostic relies on this temperature change and it's corresponding pressure change to determine if an EVAP system leak is present.

The EONV diagnostic is designed to detect leaks as small as 0.51 mm (0.020 inches). The diagnostic can determine if a small leak is present based on vacuum or pressure readings in the EVAP system. When the system is sealed, a finite amount of pressure or vacuum will be observed. When a 0.51 mm (0.020 inches) leak is present, often little or no pressure or vacuum is observed. If the test reports a failing value, DTC P0442 will set.

Canister Vent Restriction Test

If the EVAP vent system is restricted, fuel vapors will not be properly purged from the EVAP canister. The control module tests this by commanding the EVAP purge solenoid ON, commanding the EVAP vent solenoid OFF, and monitoring the FTP sensor for an increase in vacuum. If the vacuum increases more than a calibrated value, DTC P0446 will set.

Purge Solenoid Leak Test

If the EVAP purge solenoid does not seal properly fuel vapors could enter the engine at an undesired time, causing driveability concerns. The control module tests for this by commanding the EVAP purge solenoid OFF and the vent solenoid ON, sealing the system, and monitors the FTP for an increase in vacuum. If the control module detects that the EVAP system vacuum increases above a calibrated value, DTC P0496 will set.

The 15 to 85% value you are speaking of refers to a perameter that must be met for the self diagnostics to run. But they will not run every time your fuel level is between those values. The vehicle must meet the following criteria.

DTC P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0147, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0167, P0220, 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 startup engine coolant temperature (ECT) is between 4-30°C (39-86°F).

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

The startup ECT and IAT are within 9°C (16°F) of each other.

And even if all these things look right it still might not run. I have cleared some out that didn't run a month later.

LONG long long story short, your vehicle was hissing because you had a vent restriction, it looks like you fixed that restriction and no longer have the hiss or the light. You can get someone to check the IM status to see if the p0446 has ran and passed since cleared this should ease your mind. In most states the smog test is a quick check of codes to make sure there are no stored codes and that all I/M flags have run and passed.

yes i know of the parameters the test runs in, as well as it does not run every time. i thought placing "etc." next to that 15-85% would let everybody know i understand that without actually typing it out.

BESIDES all that everybody here sound so smart i appreciate the help. the 0446 is gone... the IM readiness now reads OK which means it did run a test and passed, so the fix was the purge valve or vent valve i did both since they were only 50-60$ together. now i got a 0442, which may have always been there and been masked by the lack of a complete test, but thats where i stand. thanks for the help.

helomechs · February 1, 2008

Why would you want your tank to hiss when you take the cap off? Wouldn't that mean the tank is building too much pressure? My tank doesn't hiss and has not for 171 thousand miles.

Has the MIL come back on??

the tank used to hiss because of vacuum, not pressure. when the purge solenoid opens on the intake manifold, and the vent valve closes, the tank begins a self test drawing down to 12"s of vacuum. it then times how long it holds that vacuum to determine if there is a leak. i beleuive it cant drop 1" in 5 sec or the light trips. the hiss was an indicator that the test is taking place and all is ok. if there is a leak in the tank there will be no vacuum and no hiss. if componets that administer the test do not work, there will be no vacuum and no hiss. i have already replaced the two components most likely to fix the prob ( the P0446 i get every few months) but i was hoping somebody could tell me how to test the thing without going to the dealer. no DTC hasn't returned yet. but it only comes back every few months anyways. the tank test only takes place when 11 or 12 different conditions are present. so i assume you dont know what to do either huh?

helomechs · February 1, 2008

Why would you want your tank to hiss when you take the cap off? Wouldn't that mean the tank is building too much pressure? My tank doesn't hiss and has not for 171 thousand miles.

Has the MIL come back on??

the tank used to hiss because of vacuum, not pressure. when the purge solenoid opens on the intake manifold, and the vent valve closes, the tank begins a self test drawing down to 12"s of vacuum. it then times how long it holds that vacuum to determine if there is a leak. i believe it cant drop more than 1" in 5 sec or the light trips. the hiss was an indicator that the test is taking place and all is ok. if there is a leak in the tank there will be no vacuum and no hiss. if componets that administer the test do not work, there will be no vacuum and no hiss. i have already replaced the two components most likely to fix the prob ( the P0446 i get every few months) but i was hoping somebody could tell me how to test the thing without going to the dealer. no DTC hasn't returned yet. but it only comes back every few months anyways. the tank test only takes place when 11 or 12 different conditions are present. so i assume you dont know what to do either huh?

and im not sure 99' even has this test. i have an 03' a late 03' so maybe thats why yours has never hissed, or maybe its broken too?

Norseman · March 19, 2008

i know the system vacuums out air during cold start ups 15-85% fuel level etc. and that was probably my hiss right?

Not right, the system should not be doing anything when you are at a stop.

EVAP System Operation

The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and EVAP vent solenoid to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge solenoid ON, allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent solenoid OFF, fresh air is drawn through the vent solenoid and the vent line to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge solenoid into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking.

Large Leak Test

This tests for large leaks and blockages in the EVAP system. The control module commands the EVAP vent solenoid ON and commands the EVAP purge solenoid ON, with the engine running, allowing engine vacuum into the EVAP system. The control module monitors the fuel tank pressure (FTP) sensor voltage to verify that the system is able to reach a predetermined level of vacuum within a set amount of time. The control module then commands the EVAP purge solenoid OFF, sealing the system, and monitors the vacuum level for decay. If the control module does not detect that the predetermined vacuum level was achieved, or the vacuum decay rate is more than a calibrated level on 2 consecutive tests, DTC P0455 will set.

Small Leak Test

The engine off natural vacuum (EONV) diagnostic is the small-leak detection diagnostic for the EVAP system. While previous leak detection methods were performed with the engine running, the EONV diagnostic monitors the EVAP system pressure or vacuum with the key OFF. Because of this, it may be normal for the control module to remain active for up to 40 minutes after the engine is turned OFF. This is important to remember when performing a parasitic draw test on vehicles equipped with EONV.

The EONV utilizes the temperature changes in the fuel tank immediately following a drive cycle to use the naturally occurring vacuum or pressure in the fuel tank. When the vehicle is driven, the temperature rises in the tank. After the vehicle is parked, the temperature in the tank continues to rise for a period of time, then start to drop. The EONV diagnostic relies on this temperature change and it's corresponding pressure change to determine if an EVAP system leak is present.

The EONV diagnostic is designed to detect leaks as small as 0.51 mm (0.020 inches). The diagnostic can determine if a small leak is present based on vacuum or pressure readings in the EVAP system. When the system is sealed, a finite amount of pressure or vacuum will be observed. When a 0.51 mm (0.020 inches) leak is present, often little or no pressure or vacuum is observed. If the test reports a failing value, DTC P0442 will set.

Canister Vent Restriction Test

If the EVAP vent system is restricted, fuel vapors will not be properly purged from the EVAP canister. The control module tests this by commanding the EVAP purge solenoid ON, commanding the EVAP vent solenoid OFF, and monitoring the FTP sensor for an increase in vacuum. If the vacuum increases more than a calibrated value, DTC P0446 will set.

Purge Solenoid Leak Test

If the EVAP purge solenoid does not seal properly fuel vapors could enter the engine at an undesired time, causing driveability concerns. The control module tests for this by commanding the EVAP purge solenoid OFF and the vent solenoid ON, sealing the system, and monitors the FTP for an increase in vacuum. If the control module detects that the EVAP system vacuum increases above a calibrated value, DTC P0496 will set.

The 15 to 85% value you are speaking of refers to a perameter that must be met for the self diagnostics to run. But they will not run every time your fuel level is between those values. The vehicle must meet the following criteria.

DTC P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0147, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0167, P0220, 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 startup engine coolant temperature (ECT) is between 4-30°C (39-86°F).

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

The startup ECT and IAT are within 9°C (16°F) of each other.

And even if all these things look right it still might not run. I have cleared some out that didn't run a month later.

LONG long long story short, your vehicle was hissing because you had a vent restriction, it looks like you fixed that restriction and no longer have the hiss or the light. You can get someone to check the IM status to see if the p0446 has ran and passed since cleared this should ease your mind. In most states the smog test is a quick check of codes to make sure there are no stored codes and that all I/M flags have run and passed.

yes i know of the parameters the test runs in, as well as it does not run every time. i thought placing "etc." next to that 15-85% would let everybody know i understand that without actually typing it out.

BESIDES all that everybody here sound so smart i appreciate the help. the 0446 is gone... the IM readiness now reads OK which means it did run a test and passed, so the fix was the purge valve or vent valve i did both since they were only 50-60$ together. now i got a 0442, which may have always been there and been masked by the lack of a complete test, but thats where i stand. thanks for the help.

A code P0442 most likely means one or more of the following has happened:

A loose or improperly affixed gas cap

A non-conforming gas cap (i.e. not factory/original brand)

A small leak/hole in a fuel vapor hose/tube

Other small leak in EVAP system

Faulty vent o-ring seal

Possible SolutionsWith a P0442, the most common repair is to:

Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.

Otherwise, replace the gas cap, or

Inspect the EVAP system for cuts/holes in tubes/hoses

Mikeee · February 4, 2008

When I replaced the purge valve on my 3.8 (same concept) I reversed the 2 lines by accident. Since they were not "keyed" in any manner I thought that it did not matter which went where.

Well after much troubleshooting I found my error.

The spring in the valve is not strong enough to hold the valve closed when vacuum is applied to the spring side of the port.

When plumbed correctly, the vacuum pulls the valve closed even tighter than the spring can close it.

A simple fix but took me weeks to find it.

May not fix your problem but then again.....

Norseman · January 31, 2008

Why would you want your tank to hiss when you take the cap off? Wouldn't that mean the tank is building too much pressure? My tank doesn't hiss and has not for 171 thousand miles.

Has the MIL come back on??

Norseman · February 6, 2008

the tank used to hiss because of vacuum, not pressure.

I do not believe that is correct. You're not venting properly, that is why there is a hiss.

I'd wait to see if the MIL comes back before you get to worked up. Good luck.

minibike132 · February 2, 2008

i know the system vacuums out air during cold start ups 15-85% fuel level etc. and that was probably my hiss right?

Not right, the system should not be doing anything when you are at a stop.

EVAP System Operation

The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and EVAP vent solenoid to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge solenoid ON, allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent solenoid OFF, fresh air is drawn through the vent solenoid and the vent line to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge solenoid into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking.

Large Leak Test

This tests for large leaks and blockages in the EVAP system. The control module commands the EVAP vent solenoid ON and commands the EVAP purge solenoid ON, with the engine running, allowing engine vacuum into the EVAP system. The control module monitors the fuel tank pressure (FTP) sensor voltage to verify that the system is able to reach a predetermined level of vacuum within a set amount of time. The control module then commands the EVAP purge solenoid OFF, sealing the system, and monitors the vacuum level for decay. If the control module does not detect that the predetermined vacuum level was achieved, or the vacuum decay rate is more than a calibrated level on 2 consecutive tests, DTC P0455 will set.

Small Leak Test

The engine off natural vacuum (EONV) diagnostic is the small-leak detection diagnostic for the EVAP system. While previous leak detection methods were performed with the engine running, the EONV diagnostic monitors the EVAP system pressure or vacuum with the key OFF. Because of this, it may be normal for the control module to remain active for up to 40 minutes after the engine is turned OFF. This is important to remember when performing a parasitic draw test on vehicles equipped with EONV.

The EONV utilizes the temperature changes in the fuel tank immediately following a drive cycle to use the naturally occurring vacuum or pressure in the fuel tank. When the vehicle is driven, the temperature rises in the tank. After the vehicle is parked, the temperature in the tank continues to rise for a period of time, then start to drop. The EONV diagnostic relies on this temperature change and it's corresponding pressure change to determine if an EVAP system leak is present.

The EONV diagnostic is designed to detect leaks as small as 0.51 mm (0.020 inches). The diagnostic can determine if a small leak is present based on vacuum or pressure readings in the EVAP system. When the system is sealed, a finite amount of pressure or vacuum will be observed. When a 0.51 mm (0.020 inches) leak is present, often little or no pressure or vacuum is observed. If the test reports a failing value, DTC P0442 will set.

Canister Vent Restriction Test

If the EVAP vent system is restricted, fuel vapors will not be properly purged from the EVAP canister. The control module tests this by commanding the EVAP purge solenoid ON, commanding the EVAP vent solenoid OFF, and monitoring the FTP sensor for an increase in vacuum. If the vacuum increases more than a calibrated value, DTC P0446 will set.

Purge Solenoid Leak Test

If the EVAP purge solenoid does not seal properly fuel vapors could enter the engine at an undesired time, causing driveability concerns. The control module tests for this by commanding the EVAP purge solenoid OFF and the vent solenoid ON, sealing the system, and monitors the FTP for an increase in vacuum. If the control module detects that the EVAP system vacuum increases above a calibrated value, DTC P0496 will set.

The 15 to 85% value you are speaking of refers to a perameter that must be met for the self diagnostics to run. But they will not run every time your fuel level is between those values. The vehicle must meet the following criteria.

DTC P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0147, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0167, P0220, 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 startup engine coolant temperature (ECT) is between 4-30°C (39-86°F).

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

The startup ECT and IAT are within 9°C (16°F) of each other.

And even if all these things look right it still might not run. I have cleared some out that didn't run a month later.

LONG long long story short, your vehicle was hissing because you had a vent restriction, it looks like you fixed that restriction and no longer have the hiss or the light. You can get someone to check the IM status to see if the p0446 has ran and passed since cleared this should ease your mind. In most states the smog test is a quick check of codes to make sure there are no stored codes and that all I/M flags have run and passed.