Chevy P0442 Small EVAP Leak: GM’s Seven Connections, 2000–2021

21-NA-124 handles both EVAP leak codes in one bulletin and gives each its own causes. P0442 is the small-leak code. P0455 is the large-leak code, and GM adds purge blockage as a second way it sets.

The valve conditions split between the two. A canister vent valve stuck open can set either code. A purge valve stuck open belongs to P0442, a purge valve stuck closed to P0455. An unsealed system is GM’s third P0442 cause, while the P0455 paragraph names unseated or damaged tubes.

How 21-NA-124, PDF p. 1, assigns causes to each code. The bulletin’s connection list and four-step inspection order apply to both.

These are the seven points GM calls critical connections, the ones that could likely set the leak codes. The bulletin’s reasoning is brief: it is likely that a joint on the list is not properly seated, or that its line is damaged.

Six of the seven are EVAP line joints that a technician inspects. The seventh item is whether the fuel tank cap is closed properly.

The seven critical connections in 21-NA-124, PDF p. 1, in GM’s order and wording.

The technician begins by confirming the EVAP system was properly assembled and each purge connection properly installed, watching for damage or wear along the lines at the same time. When damage turns up, GM sends the technician to a smoke test to confirm it.

Two notes in the bulletin bear on small leaks. Some leaks are noticeable only under pressure and some only under vacuum, so GM recommends checking both ways. GDS2 also has a role: cycling the purge and vent solenoids during the inspection may show a valve that sticks. These are shop procedures, not owner checks.

After the lines, the order is the vent valve, checked for a stuck-open position, then the purge valve. GM asks that the cause and correction be documented on the repair order.

This June 2023 bulletin names P0442 among four EVAP codes, with P0446, P0455 and P0449, that can set when dust gets into the system on trucks run in extremely dusty environments. Enough dust can block the canister and the canister vent solenoid. GM says the condition may be caused by normal use in severe dusty environments.

GM’s remedy is a retrofit filter installed between the air inlet and the canister. GM is explicit that this is not a warranty repair but a customer-pay alteration, with repair and payment authorization coming from the customer. The bulletin lists two parts, a filter assembly and a foam filter, and describes the filter as a maintenance item meant to be checked periodically.

Coverage by year differs between the 1500 and the heavy-duty trucks; see the application list on this page.

This bulletin covers the 2007–2010 Cadillac Escalade models, Chevrolet Avalanche, Suburban 1500 and Tahoe, and GMC Yukon and Yukon XL 1500 models. Its subject joins a lit MIL and one of four codes, P0442 included, to a fuel tank that is hard to fill and to moisture, water or corrosion at the CVS valve.

Fresh air reaches the CVS valve through a vent on a conduit attached to the fuel filler pipe, and dirt or dust in that intake can restrict the flow. Water can corrode the valve and restrict the fresh-air path while the valve is closed. Water that overfills the valve’s cyclonic filter can reach the canister and restrict refueling.

The labor figure comes from 09-06-04-028D, for vehicles repaired under GM’s Emission coverage; coverage itself is checked in GM’s Investigate Vehicle History (IVH) under Applicable Warranties. It is a time allowance, not a price.

There is nothing to add from the other two bulletins. 21-NA-124 is a diagnostic tip with no parts required, and 23-NA-073 is a customer-pay alteration that lists no labor time.

GM warranty labor time from 09-06-04-028D, PDF p. 7, for the 2007–2010 models it covers. Hours, not dollars.