New member here. Posted this to detail my experience with this code as I know it is a headache for most. In my experience, the gas cap is rarely the issue unless you can clearly determine the cap is defective.
My wife's 2007 Tahoe LTZ has 150K miles with ZERO issues. All I've done is change oil, rotate tires, tune up, and fill with gas. Oh yeah, transmission service done at 75K so due again. Anyhoo, got 2 codes about a month ago. One was the throttle position sensor code and the other the dreaded P0445 large leak code.
The TPS code is usually fairly simple. Pull the throttle body off and clean it good but DON'T MOVE THE THROTTLE VANE WHILE DOING THIS! Just spray it down generously with carb cleaner and get the gunk off. If this doesn't work to resolve the code, the sensor may actually be kaput. The sensor is built into the throttle body so the whole unit needs replaced but they are relatively cheap and simple as the new one just bolts into place and plugs in.
Now, on to the P0445 large leak code. The good news is that it is usually NOT a leak unless the gas cap is bad, which is usually NOT the case as mentioned. Of course, you'll want to make sure the cap is on properly. Also, the first thing to do is check underhood and under the truck at all the EVAP lines to make sure nothing is disconnected, loose, or split etc. The EVAP system relies on vacuum to register properly with the computer. If any of the components are not functioning or are gunked up and clogged, vacuum will not pull the way it should or not at all and this disruption in flow is interpreted as a "leak" by the computer. Voila! Check engine light!: First thing I did was change cap. Buy an AC Delco OEM cap. I did this and light stayed on. I then changed the vent solenoid under the truck. Light stayed off for about 4 days but came back on. The next thing was to replace the underhood purge solenoid. Light has been off for 3 weeks running now so this looks like this was the culprit. Cap $30. Vent solenoid $69. Purge solenoid $30. Still a lot cheaper than what a shop would've cost.
My wife's 2007 Tahoe LTZ has 150K miles with ZERO issues. All I've done is change oil, rotate tires, tune up, and fill with gas. Oh yeah, transmission service done at 75K so due again. Anyhoo, got 2 codes about a month ago. One was the throttle position sensor code and the other the dreaded P0445 large leak code.
The TPS code is usually fairly simple. Pull the throttle body off and clean it good but DON'T MOVE THE THROTTLE VANE WHILE DOING THIS! Just spray it down generously with carb cleaner and get the gunk off. If this doesn't work to resolve the code, the sensor may actually be kaput. The sensor is built into the throttle body so the whole unit needs replaced but they are relatively cheap and simple as the new one just bolts into place and plugs in.
Now, on to the P0445 large leak code. The good news is that it is usually NOT a leak unless the gas cap is bad, which is usually NOT the case as mentioned. Of course, you'll want to make sure the cap is on properly. Also, the first thing to do is check underhood and under the truck at all the EVAP lines to make sure nothing is disconnected, loose, or split etc. The EVAP system relies on vacuum to register properly with the computer. If any of the components are not functioning or are gunked up and clogged, vacuum will not pull the way it should or not at all and this disruption in flow is interpreted as a "leak" by the computer. Voila! Check engine light!: First thing I did was change cap. Buy an AC Delco OEM cap. I did this and light stayed on. I then changed the vent solenoid under the truck. Light stayed off for about 4 days but came back on. The next thing was to replace the underhood purge solenoid. Light has been off for 3 weeks running now so this looks like this was the culprit. Cap $30. Vent solenoid $69. Purge solenoid $30. Still a lot cheaper than what a shop would've cost.
