A very common trouble code with the Cadillac STS is the P0440 code. This trouble code references a number that is given to you when you plug your STS into a OBDII scanner. P0440 Indicates that something is wrong with the EVAP system. It does not allude to what that problem might be.
P0440: Evaporative Emission Control System Malfunction
Since it is only letting you know that something is wrong with the EVAP system, it is almost always accompanied by It often appears with, or is related other codes, such as:
P0440 is normally not an immediate threat to the drive-ability of your STS. Certainly anytime the service engine soon light is on, it’s good to deal with it as soon as possible though.
Cadillac STS P0440 Definition
P0440 is a universal OBDII trouble code. This means that regardless of which make or model of vehicle, the code will mean the same thing (STS or not). The code technically stands for:
Evaporative Emission Control System Malfunction
The EVAP system captures all fuel vapor from the fuel tank and sends them to the engines intake in order to be ignited in the normal combustion process. When the ECU registers that there is a problem with the EVAP system it will throw the P0440 OBDII Code.
Cadillac STS P0440 OBDII Code Symptoms
P0440 code will typically not be accompanied by any noticeable symptoms other than the smell of gas and the service engine soon light. Fuel economy may suffer.
The area around the fuel tank may smell of gas. There could also be a fuel leak. Often, this code is easily remedied by a new gas cap.
The EVAP system deals directly with fuel vapors. If these vapors are leaking from the system, you’ll often smell them faintly while operating the vehicle.
STS P0440 Trouble Code Causes
There are many things that can cause the P0440 trouble code to trigger in your Cadillac STS. Here are the most common problems that will throw the code:
- Evap System Hose– The hose that carries the fuel vapor from the fuel tank to the intake manifold can begin to leak. This will cause the P0440 code. Look for either a tear or hole in it. This is one of the most common issues that causes the code.
- Vapor Canister Purge Valve– One of the most common causes of the P0440 code is the vapor canister purge valve. It’s really easy to replace. There are a few clips that you need to find and remove.
- Faulty Charcoal Canister– The charcoal canister is often the cause of P0440.
- Fuel Tank Sending Unit– It is possible for the gasket that goes between the fuel sending unit to the gas tank to go bad. This can reduce tank pressure and throw the code.
- Fuel Cap– A bad fuel cap can cause the code to be thrown for sure. Often, you’ll get a message informing you that the fuel cap is off even when it is on. If you are getting that message, plus a P0440, it may save you a ton of time and money to replace the fuel cap and see if it goes away.
- Fuel Filler Neck– There is often a gasket where the fuel filler neck connects with the gas tank. This gasket can dry out, especially with vehicles that spend their time in dry climates. When it dries out, the fuel tank can’t hold pressure anymore.
Here’s a good YouTube video on how to diagnose P0440:
P0440 Diagnosis- Cadillac STS
A mechanic has a wide range of instruments at his disposal to diagnose what would be causing the P0440 in your Cadillac STS. Here are the most common things that are done to diagnose the code:
- The mechanic will typically check to see if there are any other trouble codes. The more trouble codes there are, the easier it can be to diagnose a problem. That’s because when they appear together in certain combinations, there will often only be only a few conditions that will throw any combination of codes at one time. There’s not a lot to go on with P0440 by itself, so gathering other codes is very important.
- After ascertaining what trouble codes appear with the P0440, the mechanic will typically inspect the EVAP system. This includes the purge valve, line, and canister.
- The mechanic will inspect the gas cap to make sure that it can handle pressure. If you are getting a warning that your gas cap is off, even when it’s on, replacing it will more than likely clear this code.
- The fuel tank pressure will be checked and monitored.
- After for the checks and fixes listed above, the mechanic will perform two tests. The first is a smoke test. In the second test they conduct, they use a scan tool to confirm that the EVAP solenoids and valves are operating properly.
Most Common P0440 Fixes
Here are the most common STS P0440 fixes:
- Gas cap replacement
- EVAP line replacement
- Replace charcoal canister
- Replace the fuel tank
Of all the items listed above, it would be wise to start with the gas cap and work your way to the fuel tank, since the gas cap is far and away the easiest and least expensive items to replace on here.
Here’s a great video on how to test your gas cap.
Good luck figuring out what is causing your Cadillac STS to throw the P0440 code. We hope this helps. If there is anything that you feel like you could add, please feel free to leave a comment below.
Is P0440 a Serious Concern?
While P0440 is not going to cause the STS‘s engine to stop running, it should not be treated lightly. You could have a fuel leak. Pay extra attention to your tank level and make sure you are not leaking fuel. We recommend taking it in and/or dealing with it right away.