P0442 Code on a Cadillac: EVAP System Small Leak Detected (Cadillac Guide)

P0442 on a Cadillac is GM's "Evaporative Emission (EVAP) System Small Leak Detected": the engine computer sealed the fuel vapor system, watched it, and decided it was losing pressure or vacuum through a hole about 0.020 inch across. It won't hurt the engine, but it is the EVAP code Cadillac owners chase longest, because the test runs only under narrow conditions. The surprise is how specific GM's Cadillac paperwork gets: a 2013 ATS hose that rubs on the engine cover, a filler-pocket rubber that rolls over the neck, a 2012 CTS vent valve under special coverage and a broken filler vent connector on the 2013–2014 Escalade all set this exact code. And every Cadillac reports its smallest leak as P0442 — no Cadillac in GM's tables uses P0456.

What Does P0442 Mean on a Cadillac?

Gasoline in the tank gives off vapor all the time. The EVAP system stores that vapor in a charcoal canister and later lets the engine draw it in and burn it through a purge valve. A canister vent valve lets fresh air into the canister, and a fuel tank pressure sensor tells the engine control module (ECM) what is happening inside the system.

To check for leaks, the ECM closes the vent valve so the tank, filler neck, cap (or capless filler), lines and canister form one sealed volume. GM's 2019 diagnostic tables for the engine group that covers most Cadillac V6s and the Escalade's 6.2L V8 describe the small-leak test as detecting a leak of 0.020 inch anywhere between the fuel fill cap and the purge solenoid.

That is a pinhole. GM's diagnostic tip bulletin 21-NA-124, which names Cadillac and covers 2000–2023 gasoline vehicles, adds the part most owners miss: P0442 can also set from a purge valve or vent valve stuck slightly open, not only from a hole. For the cross-brand overview, see our GM EVAP leak codes guide (P0442/P0455).

Which Cadillacs Set P0442

Every gasoline Cadillac from the late 1990s on. We searched GM's published OBD tables for Cadillac engines from 1996 to 2025. What changes over the years is the leak size the test looks for and how it runs.

So if a generic reader shows P0456 on a Cadillac, re-read it with a tool that shows GM descriptions. In GM's tables P0456 belongs only to supplier engines in Saab, the Saturn Astra, the Aveo and a few others. We explain that on our P0456 page.

How a Cadillac Runs the Small-Leak Test

Knowing the test explains why P0442 can take a week to come back — or to prove a repair.

On current Cadillacs, GM uses engine-off natural vacuum. After you park a warm car, the ECM checks fuel volatility, closes the vent, and watches tank pressure rise during the hot soak and then fall into vacuum as the fuel cools. A sealed system builds and holds both; a leaking one doesn't. GM's 2019 table for that engine group lists the enable conditions:

• Fuel level between 10% and 90%
• At least 600 seconds of drive time and 5 miles before shut-off
• Coolant at or above 63 °C, and an estimated outside temperature between 0 and 35 °C
• The test runs during the hot soak, for up to 2,400 seconds

GM averages the results (an "EWMA") over several completed tests. The light comes on when the average passes 0.59 and goes off only after it stays below the re-pass level for three more trips — one good night doesn't clear it.

Older Cadillacs did it differently. The 1998–2003 front-drive Northstar cars pulled engine vacuum on the sealed system once per cold start and measured the decay. The Catera and the 2004 rear-drive Northstar used European-style calibrations that calculate a leak size from the pressure change.

What GM's Cadillac Documents Say

GM has issued a surprising number of Cadillac-specific documents for this code. Each points at a different part, which is why "replace the gas cap" is so often the wrong first move.

2013 ATS 3.6L (LFX) — a hose that rubs through (PI0872, December 2012). On cars built before November 1, 2012, the EVAP pipe can rub against the engine cover, the battery cable or the diagonal brace and wear a hole. GM's fix is to slide a 435 mm piece of conduit over the nylon section, or replace the pipe if it is already damaged.

2013 ATS — a vent valve that only leaks under vacuum (PI0979, May 2013). The canister vent solenoid can seal when pressurized but leak under vacuum — and the small-leak test runs under vacuum. A standard smoke machine pressurizes to no more than about 13 inches of water, so the leak may never show. GM's procedure: command the vent closed, open purge to pull vacuum, seal the system and watch for decay; replace the vent solenoid if it leaks down. GM also says do not replace the canister unless it fails the leak test.

2013–2015 ATS sedan — the filler-pocket rubber (PIC6030, September 2014). On cars built before August 9, 2014, the rubber insulator in the fuel filler pocket can be rolled over the filler neck. Roll it back into place and check the cap seal for damage.

2012 CTS — a vent valve that doesn't fully close (12154C and Special Coverage 14264). Bulletin 12154C says the vent valve on some 2012 CTS may not fully seal and "may falsely indicate a leak" and set P0442. Special Coverage 14264 then covered the valve on 2012 CTS with the 3.0L (LFW), 3.6L (LFX) or 6.2L (LSA) for 10 years or 120,000 miles from the in-service date. For a 2012 CTS that window has passed for practical purposes, though a dealer VIN check is free.

2013–2014 Escalade, ESV and EXT — fuel smell while filling (15-NA-019). A fractured connector on the filler neck recirculation line can cause a strong fuel odor during fill-ups or at idle and set P0442 or P0455. The fix is a new fuel tank filler vent hose.

2019 XT5 — the canister itself (PIE0528, July 2019). This engineering request names P0442 with P0455, P0446, P0449 and P0498, and describes two leak points GM wanted returned: the O-ring between the canister body and the vent solenoid, and the fresh-air filter box.

NHTSA also lists older Cadillac items naming P0442 that it holds only as summaries: bulletin 3003 for the front-drive Northstar cars ("inspect at fuel filler neck"), 01680 for the 2004 CTS and SRX, 3078 for the 2004 Escalade, and TB-09-06-04-024 for the 2008–2009 Escalade, which concerns the fuel tank pressure sensor.

Symptoms of P0442

• Check engine light — often the only symptom
• A faint fuel smell near the rear of the car or the filler door
• A strong fuel odor while filling or idling on a 2013–2014 Escalade (15-NA-019)
• Other EVAP codes alongside it — P0446, P0449 or P0498 on the 2019 XT5 in GM's request
• Rough idle or stalling only if a purge valve is also stuck partly open

Causes and How to Confirm Each

How Is P0442 Diagnosed on a Cadillac?

1. Read every code with GM descriptions. P0442 with vent codes points toward the vent valve; P0442 with P0496 points toward the purge valve.
2. Check your VIN for open bulletins and coverages — a dealer check is free.
3. Don't disturb anything first. GM's PIT4943D, which NHTSA lists against Cadillacs from the 2000 Catera to the 2016 CT6, says not to touch fuel system parts after verifying P0442, so the leak is still there to find.
4. Inspect GM's seven connections from 21-NA-124: purge tube at the purge valve, purge tube to chassis line near the transmission, chassis line at the canister, tank load line at the canister, vent valve line, tank load line jumper near the tank, and the fuel cap.
5. Follow GM's order: lines seated, lines undamaged, then the vent valve, then the purge valve.
6. Smoke test under both pressure and vacuum, never above 13 inches of water (0.5 psi). On a 2013 ATS add PI0979's purge-and-seal vacuum test.
7. Replace only what the test proves — and the canister only if it fails.
8. Clear the code and let the monitor run: fuel between a quarter and three-quarters, drives of at least 10 minutes and 5 miles, then park and let it sit. Expect several days.

Parts and Cost

GM Documents That Name P0442 on a Cadillac

Have a dealer check your VIN for open bulletins and coverages rather than relying on any article, including this one.

What Other P0442 Pages Get Wrong

• "Just tighten the gas cap." GM's Cadillac documents point at hoses, vent valves, filler rubbers and canister seals far more often than caps — and many newer Cadillacs have a capless filler.
• "A smoke test will find it." GM's 2013 ATS bulletin says a pressure-only smoke test can miss a vent valve that leaks only under vacuum.
• "Replace the canister." GM says not to unless it fails the leak test.
• "Your Cadillac might show P0456 instead." No Cadillac in GM's tables uses P0456; even the Saab-shared 2011 SRX 2.8T uses P0442.
• "It should clear after one drive." GM averages several engine-off tests before turning the light off.

Frequently Asked Questions

Is P0442 serious on a Cadillac?

Not mechanically. It means a small vapor leak — the engine will run normally. It will keep the check engine light on and fail an emissions inspection, and a fuel smell is worth fixing promptly.

Can a loose gas cap cause P0442?

Yes, and the cap is one of GM's seven connections to check. But on a Cadillac GM's own documents more often find a rubbed hose, a vent valve or a filler-pocket rubber, so don't stop at the cap.

Why does the code come back days after I clear it?

Because the test runs only after a warm drive, with the right fuel level and temperature, while the car sits parked. GM averages several of those tests before deciding.

Does my 2013 ATS have a known P0442 problem?

GM issued three: PI0872 (EVAP pipe rubbing on 3.6L cars built before November 1, 2012), PI0979 (vent solenoid leaking under vacuum) and PIC6030 (filler-pocket rubber on sedans built before August 9, 2014). A dealer can check which apply to your VIN.

Is the 2012 CTS vent valve still covered?

Special Coverage 14264 ran 10 years or 120,000 miles from the in-service date, so for practical purposes it has ended. A dealer VIN check is free if you want to be sure.

Can I drive with P0442?

Generally yes. Get it diagnosed before your next emissions test, and sooner if you smell fuel.

Should I replace the purge valve or the canister first?

Neither until a test points to it. GM's sequence is lines, then the vent valve, then the purge valve — and the canister only if it fails the leak test.