P0440 Code on a Cadillac: EVAP System Malfunction (Cadillac Guide)

P0440 on a Cadillac is GM's "Evaporative Emission Control System Malfunction" — and on the Cadillacs that actually use it, it is the large-leak code before P0455 existed. GM's tables for the 1998–2003 Northstar DeVille, Seville and Eldorado describe P0440 as a test that catches "a missing gas cap, a 'gross' leak in the evap system or a failed (stuck) closed purge valve." The same code covers the 1999–2002 Escalade, the 2003 CTS and the Opel-built Catera. The surprise: from 2004 on, no Cadillac table we found lists P0440 at all — so on a newer Cadillac, a P0440 reading usually means the scanner, not the car, is telling the story.

What Does P0440 Mean on a Cadillac?

The evaporative emission (EVAP) system traps gasoline vapor from the tank in a charcoal canister. While the engine runs, the engine computer (PCM) opens a purge solenoid to draw that vapor into the intake and burn it. A vent valve at the canister lets air in behind it, and a fuel tank pressure (vacuum) sensor reports what is going on in the tank.

To check the system, the PCM closes the vent and keeps purging. In a sealed system, engine vacuum pulls the tank into vacuum within a set amount of purge flow. If it can't, the PCM sets P0440. GM's 2000–2003 Northstar tables put it plainly: the code "will detect a weak vacuum condition (large leak or purge blockage) in the Evap. system."

That is exactly what later Cadillacs call P0455. In other words, on a 1998–2003 Cadillac, P0440 is not a vague "something is wrong with the EVAP system" code — it is a specific test with two possible answers: air is getting in (cap, hose, filler neck, vent valve) or no vacuum is getting through (purge solenoid stuck closed, blocked line).

Which Cadillacs Use P0440

We searched GM's published OBD tables for every Cadillac engine from 1996 to 2025.

One caution: GM's 2002 truck table names the 5.3L and 6.0L LQ4 engines but not the Escalade's 6.0L LQ9 by name, so we can't confirm from it how a 2002 Escalade 6.0L reports this test.

How the Northstar Test Works

The 1998–2003 front-drive Northstar cars run a cold-start vacuum test. GM's 1998 table describes it this way:

• It runs once per cold start, when start-up coolant and intake air temperatures are both between about 2 and 33 °C and within 14 °C of each other — in other words, after the car has sat overnight.
• Fuel level must be between 10% and 90%.
• With the vent closed and purge running, the tank must reach 8.5 inches of water of vacuum before about 20 grams of purge flow pass. If not, P0440 sets. GM sizes that failure as a leak larger than 0.080 inch.
• If the system does pull down, the PCM moves on to watch the vacuum decay — that is the P0442 small-leak test, which in 1998 looked for leaks between 0.040 and 0.080 inch.

By 2003 the wording had become "Purge Volume > 3 liters before Tank Vacuum > 8.0 inches of water," with fuel between 15% and 85% and coolant below 30 °C at start. The idea is the same: if purge flows and the tank doesn't respond, something is open or something is blocked.

Two companion codes matter on these cars. P1441 is the opposite failure — GM calls it "continuous open purge flow," a purge solenoid leaking vacuum into the tank. And on the 2000–2002 DeVille, NHTSA lists a GM item on intermittent P0443, the purge solenoid circuit code.

Escalade, CTS and Catera

Escalade. GM's 1999 and 2002 truck tables describe P0440 as a "weak vacuum condition (large leak or restriction)" with two stages: a cold test, and a warm follow-up test that runs only if the cold test failed on the previous trip and again on the current one. Fuel level has to be roughly between an eighth and seven-eighths.

2003 CTS 3.2L. The first CTS shared its diagnostic table with the 3.0L V6 used in Saturn models, and the test is written in the same European style as the Catera's. Its P0440 runs with the car stopped at idle, in closed loop, and fails if the tank doesn't respond while purging — GM's table labels it "Large Leak." From 2004 the CTS reports the same fault as P0455.

Catera. The Opel-built Catera is the odd one out: its 1997–2001 tables list both P0440 and P0455. P0440 is a set of tank-pressure checks run at idle with the car stopped (including tank pressure while the purge solenoid opens), and P0455 is the dedicated large-leak result. Both need the engine running for a while first — more than 1,005 seconds after start in the 1997 table.

GM's Cadillac Bulletins

2002 DeVille — P0440 after filling up (September 2002). NHTSA's summary of this GM item describes a Service Engine Soon message, engine stumble or stalling, or P0440 for a large leak set after filling the vehicle, with possible damage to the fuel tank or fuel level vent valves, or the EVAP canister flooded with raw fuel. NHTSA holds only the summary, so we could not read GM's full procedure — but it points to the same overfill problem GM documented a decade later for P0455 on the XTS.

Northstar filler neck (bulletin 3003). NHTSA lists a GM item for 1996–1999 DeVille, Eldorado and Seville: "DTC P0442 small leak detected, inspect at fuel filler neck." It names P0442, not P0440, but a leaking filler neck can fail either test.

GM's EVAP leak tip (21-NA-124). This bulletin covers 2000–2023 GM gasoline vehicles, Cadillac included, and is written for P0442 and P0455. Its method — check seven connections, then the vent valve, then the purge valve, and smoke test under pressure and vacuum — fits P0440 on a 2000–2003 Cadillac too, because GM's own definition of P0440 on those cars is the same "large leak or purge blockage" test.

Symptoms of P0440

• Check engine light or Service Engine Soon message — usually the only symptom
• Fuel smell around the filler or the rear of the car
• Stumbling or stalling after a fill-up (the 2002 DeVille item) if raw fuel has reached the canister
• P0442, P1441 or P0443 stored alongside it on Northstar cars

Causes and How to Confirm Each

How Is P0440 Diagnosed on a Cadillac?

1. Confirm the car actually stored P0440. On a 2004-or-later Cadillac, re-read it with a GM-capable scanner; GM's tables for those years use P0455.
2. Note every companion code. P0442 means the system pulled down but leaked; P1441 means purge is leaking through; P0443 is the purge solenoid circuit.
3. Check the cap and filler neck. On a Northstar car, include the filler neck GM's 3003 item points to.
4. Inspect the lines between the purge solenoid, the canister and the tank for disconnection, cracks or kinks — the same seven-connection idea as 21-NA-124.
5. Command the purge solenoid and vent valve with a bidirectional scan tool and watch the tank vacuum reading. No vacuum with purge on and vent closed means a big leak, a stuck-open vent or a stuck-closed purge.
6. Smoke test under pressure and vacuum, keeping pressure at or below about 13 inches of water.
7. If the problem began at a fill-up, check for liquid fuel in the canister and lines before replacing valves.
8. Clear the code and let the car sit overnight. The test runs only on a true cold start, so confirmation can take a few days.

Parts and Cost

GM Documents Relevant to P0440 on a Cadillac

None of the full GM bulletins we could read names P0440 on a Cadillac; the only Cadillac item that does is the 2002 DeVille summary. Have a dealer check your VIN for open bulletins and coverages rather than relying on any article, including this one.

What Other P0440 Pages Get Wrong

• "P0440 is a general EVAP fault." On the Cadillacs that use it, GM defines a specific large-leak or purge-blockage test.
• "It's always the gas cap." GM's Northstar definition also names a stuck-closed purge valve.
• "Any Cadillac can set P0440." We found it only in 1997–2003 Cadillac tables. Newer Cadillacs use P0455.
• "Clear it and check tomorrow." The Northstar test needs a true cold start with matching coolant and air temperatures.

Frequently Asked Questions

Is P0440 serious on a Cadillac?

It won't damage the engine. It means fuel vapor may be escaping or the purge system isn't working. If it started after a fill-up and the car stumbles, get it checked soon.

What's the difference between P0440 and P0455 on a Cadillac?

Mostly the model year. GM's 1998–2003 Northstar, 1999–2002 Escalade and 2003 CTS tables report the large-leak test as P0440; 2004-and-later Cadillacs report it as P0455. The Catera used both.

Can a gas cap cause P0440?

Yes. GM's 1998 Northstar definition names a missing gas cap first. Check the seal and reseat it, then let the car complete a cold-start test.

My 2015 Cadillac shows P0440. What now?

GM's tables for that era don't list P0440. Re-read the code with a scanner that shows GM descriptions; you're most likely looking at P0455 or another EVAP code.

Why didn't the code come back after I cleared it?

The Northstar test runs only on a cold start with coolant and air temperatures close together, so it may not have run yet. Give it several overnight cold starts.

Does P0440 mean the purge valve is bad?

Not necessarily. A stuck-closed purge valve is one cause, but so are a loose cap, a cracked hose and a vent valve stuck open. Test before replacing.

Can I drive with P0440?

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