Chevy P0446: GM EVAP Vent Fixes for Silverado, Tahoe, Cruze

P0446 appears in three GM service bulletins, each written for a different set of vehicles and each with its own cause. Two of them, 23-NA-073 and 09-06-04-028D, also list P0442, P0455 and P0449. 17-NA-233 lists P0446 alone.

GM bulletins that list P0446, with the vehicles each one covers.

23-NA-073 is a June 2023 technical bulletin for Silverado and Sierra trucks, 1500 and heavy duty. Its condition is narrow: customers who operate their trucks in extremely dusty environments may get dust into the EVAP system, enough to plug the canister and the canister vent solenoid.

The retrofit places an in-line filter on the canister vent hose. GM’s service procedure for modifying the hose is written for technicians. Because the work is a customer-pay alteration, the bulletin carries no warranty labor time, and it needs the owner’s authorization.

The filter does not end the matter. GM describes it as a maintenance item to be checked periodically so the code does not return, and says that when a retrofitted truck comes back with the condition, the repair can be the filter.

09-06-04-028D, revision D from April 2014, pairs P0446 with a fuel tank that is hard to fill. GM’s explanation centers on the CVS valve, which pulls fresh air into the EVAP system via a vent atop a conduit fastened to the fuel filler pipe.

Three things can go wrong on that path. Dirt and dust can restrict airflow. Water can reach the valve, corrode it and restrict the fresh-air intake when the valve is closed. And water caught by the valve’s cyclonic filter can, once the filter’s capacity is exceeded, get into the canister and restrict refueling.

The revised valve assembly, P/N 20995472, is the replacement GM specifies for all vehicles in the bulletin, the 2008–2009 hybrids included.

17-NA-233 covers the 2016–2019 Chevrolet Cruze with the 1.4L LE2. The complaint is a lit MIL, the code is P0446, and the cause is water trapped in the evaporative emission canister filter pipe.

GM’s correction replaces that pipe with a newly designed one, P/N 42708103 for 2016–2017 and 42703257 for 2018–2019. The labor operation is titled Evaporative Emission Canister Filter Relocation, and the procedure, written for technicians, gives the new pipe an added mounting point on the wheelhouse panel.

The bulletin’s second version, released November 21, 2019, added the 2018–2019 model years.

09-06-04-028D and 17-NA-233 each list one labor operation, both under GM’s Emission coverage, and both mark it as unique to the bulletin. The figures are hours; neither bulletin gives a price. 23-NA-073 lists no labor time because the dust filter is customer pay.

GM warranty labor time for P0446 repairs, from 09-06-04-028D, PDF p. 7, and 17-NA-233, PDF p. 4. Hours, not dollars.

Each of these bulletins states that it is meant for professional technicians, not do-it-yourselfers, and that a described condition may not apply to a given vehicle. Owners are pointed to a GM dealer to ask whether their vehicle may benefit from a bulletin. Details worth bringing: the model year and engine, the stored codes, whether the tank is hard to fill, and whether the truck works in heavy dust.