P0455 Code on a Cadillac: EVAP System Large Leak Detected (Cadillac Guide)

P0455 on a Cadillac is GM's "Evaporative Emission (EVAP) System Large Leak Detected" — but GM's own definition is broader than the name. The engine computer tried to pull vacuum on the fuel tank and couldn't, which GM describes as "a weak vacuum condition (large leak or purge blockage)." So a Cadillac can set P0455 with nothing leaking at all: a purge valve stuck shut gives the same result as a missing cap. GM's Cadillac documents prove it — the best-known one, for the 2013 XTS, ties P0455 to topping off the tank and a purge valve that sticks, not to a hole. And if you own a pre-2004 Cadillac, the same fault usually shows up under a different number entirely.

What Does P0455 Mean on a Cadillac?

The EVAP system catches gasoline vapor from the tank in a charcoal canister. When the engine is running, the engine control module (ECM) opens a purge valve to draw that vapor into the intake and burn it, while a canister vent valve lets fresh air in behind it.

To run the large-leak test, the ECM closes the vent valve and keeps purging. With the system sealed, engine vacuum should quickly pull the tank into vacuum, which the fuel tank pressure sensor reports. If a set amount of purge flow goes by and the tank still hasn't reached its target, the ECM sets P0455.

That result has two very different explanations. Either air is getting in faster than the engine can pull it out — a large leak — or no vacuum is reaching the tank because the purge path is blocked. GM's diagnostic tip bulletin 21-NA-124, which names Cadillac and covers 2000–2023 gasoline vehicles, lists the usual suspects: an unseated tube connection, a damaged tube, a vent valve stuck open or a purge valve stuck closed.

For the cross-brand picture, see our GM EVAP leak codes guide (P0442/P0455).

Which Cadillacs Set P0455

We checked GM's published OBD tables for Cadillac engines from 1996 to 2025. The code's history on Cadillac is unusual, because the German-engineered Catera used it years before GM's own engines did.

So if a generic scanner shows P0455 on a 1998–2003 DeVille, Seville or Eldorado, re-read it: GM's tables for those cars use P0440 for this test.

How a Cadillac Runs the Large-Leak Test

GM's 2019 table for the engine group that covers most Cadillac V6s and the Escalade's 6.2L describes the test this way:

• It runs once per cold start, with fuel between 10% and 90%, system voltage at least 10 volts and barometric pressure above 70 kPa.
• The ECM closes the vent and purges. If about 9 liters of purge flow pass before tank vacuum reaches its passing level of 2,740 Pa (roughly 11 inches of water), the test fails.
• The test can take up to 1,400 seconds, depending on driving.
• After a failure GM runs a "weak vacuum follow-up test," which it also calls the fuel cap replacement test — so if the cap really was the problem, the system can confirm the fix without waiting for another full cold-start test.

The 2004 rear-drive Northstar tables add a twist: besides the decay test, a "fuel cap missing" strategy watches whether vacuum builds while driving, and the same P0455 is used when the vent valve is stuck open. On those cars a failed vent valve and a missing cap set the same code.

What GM's Cadillac Documents Say

2013 XTS — topping off the tank (PI0898, January 2013). GM says P0455 on the XTS "may be caused by over filling (topping off) the fuel tank or by filling the fuel tank using a damaged service station fuel fill nozzle." If diagnosis finds the purge solenoid sticking, GM's fix is to replace both the purge solenoid and the canister and to blow out every EVAP line with compressed air at no more than 5 psi, because liquid fuel left in the lines can make the code come back. GM also warns technicians not to prop open the capless filler flaps with a screwdriver — they can be damaged — and asks dealers to tell the owner: once the nozzle clicks off, stop.

2013–2014 Escalade, ESV and EXT — fuel smell while filling (15-NA-019, December 2015). A fractured connector on the filler neck recirculation line can cause a strong fuel odor during fill-ups or at idle and set P0455 or P0442. The fix is a new fuel tank filler vent hose; GM lists separate part numbers for the Escalade and for the ESV/EXT.

2019 XT5 — canister leak points (PIE0528, July 2019). GM engineering asked dealers to return canisters from XT5s with P0455, P0442, P0446, P0449 or P0498 that leaked at the O-ring between the canister body and the vent solenoid, or through the fresh-air filter box.

2008–2009 Escalade — tank pressure sensor (TB-09-06-04-024). NHTSA's summary describes diagnostic information for P0455 alongside P0442, P0446 and P0451–P0454, and replacement of the fuel tank pressure sensor or module. We could read only the summary, not the bulletin itself.

Purge valve coverages. Because a purge valve stuck closed can set P0455, it is worth knowing GM's Cadillac purge coverages, even though none lists P0455 by name: Special Coverage 18029 (2015 ATS, CTS, SRX and XTS; 10 years or 120,000 miles, now largely passed) and N222369620 (2019 XTS 3.6L; 15 years or 150,000 miles, still running). Both use GM purge valve 12690512.

Symptoms of P0455

• Check engine light — usually the main symptom
• A "check fuel cap" style message on models that display one
• Fuel smell at the filler or under the car, especially while refueling (2013–2014 Escalade bulletin)
• Rough running or stalling after a fill-up if the purge valve is involved
• Other EVAP codes with it — vent (P0446, P0449) or tank pressure sensor codes point the diagnosis

Causes and How to Confirm Each

How Is P0455 Diagnosed on a Cadillac?

1. Read all codes with GM descriptions. Vent or sensor codes alongside P0455 change where you start.
2. Check your VIN for open bulletins and coverages, especially on a 2019 XTS.
3. Check the cap or capless filler. If you reseat a loose cap, GM's follow-up test is designed to confirm that fix.
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 cap.
5. Cycle the purge and vent valves with a bidirectional scan tool, as GM recommends, watching tank vacuum. No vacuum with purge open and vent closed means a blockage, a stuck purge valve or a stuck-open vent.
6. Smoke test under pressure and vacuum, keeping test pressure at or below 13 inches of water.
7. If the purge valve is sticking after a top-off, follow PI0898's lesson: find and clear liquid fuel in the lines, or the new valve won't last.
8. Clear the code and drive through a few cold starts with the tank between a quarter and three-quarters full.

Parts and Cost

GM Documents That Name P0455 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 P0455 Pages Get Wrong

• "It's always the gas cap." GM defines P0455 as a large leak or purge blockage; the 2013 XTS bulletin is about a stuck purge valve.
• "Clear it and wait weeks." GM runs a follow-up test after a failure, so a genuinely fixed cap problem can be confirmed sooner.
• "Every Cadillac uses P0455." 1998–2003 Northstar cars, 1999–2002 Escalades and the 2003 CTS use P0440 for this test in GM's tables.
• "Just replace the purge valve." If fuel has flooded the lines, GM's fix includes the canister and blowing out the lines.
• "Topping off is harmless." GM names it as a cause of P0455 on the XTS.

Frequently Asked Questions

Is P0455 serious on a Cadillac?

It isn't an engine-damage code, but it means fuel vapor is escaping or the purge system isn't working. If you smell fuel, have it checked promptly.

Can a gas cap cause P0455?

Yes. A missing or loose cap is the textbook cause, and GM's follow-up test is designed to confirm a cap fix. But a stuck purge valve or vent valve sets the same code.

My XTS has a capless filler. What can leak?

The capless flaps and seals can be damaged, which is why GM tells technicians not to pry them open with a screwdriver. GM's XTS bulletin also points to the purge valve and canister after overfilling.

Why does my Cadillac set P0455 right after a fill-up?

On the 2013 XTS GM ties it to topping off the tank, which can push liquid fuel into the EVAP system. On a 2013–2014 Escalade a fuel smell while filling points to the filler vent hose connector in 15-NA-019.

Is the purge valve on my XTS covered?

The 2019 XTS 3.6L has Special Coverage N222369620 for a purge valve that doesn't fully close, for 15 years or 150,000 miles. The 2015 XTS was in Special Coverage 18029, whose 10-year term has largely passed. A dealer VIN check is free.

Why would a scanner show P0455 on my 2002 DeVille?

GM's 2002 Northstar tables use P0440 for this test, not P0455. A generic reader may be showing a different code than the car stored — re-read it with a GM-capable tool.

Can I drive with P0455?

Usually, yes, but it will fail an emissions inspection, and a fuel smell is a reason not to wait.