I own a 2000 Chevrolet Silverado and am experiencing a recurring P0446 diagnostic code. The code appears only when my fuel tank reads half or less, but disappears entirely when the tank is full. I've already replaced the EVAP canister vent control valve and filter, yet the issue persists. Why does this happen? Is there a known fix or troubleshooting step specific to this model year?
I replaced the EVAP Canister Vent Control Valve. Any suggestions or further troubleshooting steps would be greatly appreciated!
P0446 indicates a circuit issue. Start by verifying 12 volts at the vent valve with the key off (KOEO). Did you follow the GM TSB #02-06-04-037F when replacing the valve? This may help ensure proper installation and function.
No, I did not use the TSB during replacement. That was my oversight — thanks for pointing it out.
This might be a software or sensor timing bug. I experience the same P0446 code when fuel levels drop below half, and it clears once I refill the tank.
I have the exact same problem — replaced both filter and vent valve, and I'm getting 12 volts at the plug. Anyone else with this issue? KEV, any ideas?
Looking for the ohm specifications of the vent valve. Without a scanner, you can manually test whether the vent valve opens (releases vacuum) when the tank is full. If it's stuck or there’s restriction in the line, that could cause P0446. Note: The code sets when the EVAP system fails to release vacuum quickly enough. You can verify this by using a scanner — close the vent valve, open it during purge cycle, and monitor TPS readings as pressure returns to atmospheric levels.
I've been troubleshooting this P0446 code for over two months. I’ve confirmed good voltage at all electrical connectors and have replaced multiple components. My key observation: when I fill the tank to about three-quarters full, the check engine light goes off and no code appears on scan — not even a yellow warning. The issue only triggers when I refill below half capacity. Please don’t suggest simply 'don't fill the tank' as a solution. Any real technical insights or diagnostics would be helpful.
You mentioned replacing the EVAP Canister Vent Control Valve — confirm that was done correctly. First, check for 12 volts at the vent valve with the key off (KOEO). There's a GM Technical Service Bulletin (TSB) relevant to this issue: TSB #02-06-04-037F. Search online for a copy if needed. Also note: the Powertrain Control Module (PCM) does not perform EVAP system checks when the fuel tank is full, so the code only triggers under low-fuel conditions.