P0440, P0441, P0442, P0446 EVAP codes on GM vehicles
Shops report problems with P0440, P0441, P0442, P0446 EVAP codes on GM vehicles. In order to troubleshoot any of the GM EVAP codes, it’s important to understand how the system works. The evaporative emissions system is designed to prevent raw gas vapors from entering the atmosphere. That means the entire fuel supply system must be sealed and tested on a regular basis.
Gas vapors are absorbed by a canister of activated charcoal. When certain driving conditions are met, the engine sucks the gas vapors out of the canister and allows fresh air in to completely purge the charcoal. The gas vapors are burned by the engine.
However, before the computer performs a “purge” cycle, certain conditions must be met. For example: The computer wants to avoid dumping gas vapors into a cold engine. So it checks barometric pressure, intake air temperature, engine coolant temperature, and fuel level. In addition, the computer checks how long the vehicle has been in the off condition and the miles driven since the last purge cycle and EVAP test.
Once those conditions are met, the computer opens the vent and purge solenoid valves and purges the canister. At the completion of the purge, the computer closes the vent valve (closing off the fresh air) and leaves the purge valve open (to pull a vacuum on the system.) Then it closes the purge valve and watches the fuel tank pressure sensor to see if the correct vacuum level was achieved. If it isn’t, the computer determines how large or small the leak is by the vacuum level achieved as compared to what it should be. It retains this information in memory until it conducts the test a second time. If the system fails two times in a row, it will light the check engine light and provide a code.
The computer also monitors voltage readings to the purge and vent solenoids. By monitoring the voltage drop on the power and ground wires, it can determine whether the solenoid activated. (Whether the mechanical part of the valve opened and closed properly or sealed properly is an entirely different question).
A P0445 code usually indicates a bad seal on the gas cap or a defective cap. If you have rust forming around the filler tube, that would cause a large leak. If the O-ring on the gas cap is worn, distorted, or missing, that would also be a large leak.
A P0442 small leak is usually caused by a crack in the vacuum hose somewhere in the system. It can also be caused by dirt or spider webs blocking the complete sealing of the purge or vent solenoids. GM has reported some issues with spiders building nests in the vent solenoid which prevents it from sealing properly. They’ve issued TSBs for vehicles most prone to the problem and released new vacuum lines that contain a spider blocking screen.
Shops use a special low pressure smoke machine with nitrogen to pressurize the system and find leaks. Under NO circumstances should you inject compressed air into this system. First, it cannot handle high pressure. Second, the compressed air will pick up fuel vapors and turn the leak into a potential flame thrower.
You can check for cracks in vacuum lines by squeezing the line and examining with a flashlight. If you get a valve circuit malfunction code, you’ll need to purchase a subscription to eautorepair for the wiring diagram and testing procedure.
P0441 Evaporative Emission Control System Incorrect Purge Flow
P0442 Evaporative Emission Control System Leak Detected (small leak)
P0443 Evaporative Emission Control System Purge Control Valve Circuit Malfunction
P0444 Evaporative Emission Control System Purge Control Valve Circuit Open
P0445 Evaporative Emission Control System Purge Control Valve Circuit Shorted
P0446 Evaporative Emission Control System Vent Control Circuit Malfunction
P0447 Evaporative Emission Control System Vent Control Circuit Open
P0448 Evaporative Emission Control System Vent Control Circuit Shorted
P0449 Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction
P0450 Evaporative Emission Control System Pressure Sensor Malfunction
P0451 Evaporative Emission Control System Pressure Sensor Range/Performance
P0452 Evaporative Emission Control System Pressure Sensor Low Input
P0453 Evaporative Emission Control System Pressure Sensor High Input
P0454 Evaporative Emission Control System Pressure Sensor Intermittent
P0455 Evaporative Emission Control System Leak Detected (gross leak)
P0456 EVAP Leak Monitor Small Leak Detected
© 2012 Rick MuscoplatPosted on by Rick Muscoplat