OBD II P0440 Code



Hello, I have a 1998 Buick Lesabre that has a check engine light on and a p0440 code. This happened after I had repair work done. The gas tank sender unit was replaced. I took the vehicle back to the place that did the work and they insisted that the work performed was all right and that would not cause the issue. I changed the gas cap and now I am stuck… any ideas on what next to look at?


Try erasing the code.


never erase a code, unless you know what it is, whats gonna happen, and know what your doing, i suggest talking to the person who did your repair work, and make them fix it.


Code P0440 is gas cap loose, purge solenoid failed, or cannister plugged; none of which is vital to keep mobility. If the problem is still there, the code will show up again.


oh, sorry, by the way you said it i assumed you didnt know what you were saying.


When I had that code on my 98 Buick it turned out to be a bad “fuel tank pressure sensor”. It’s a $56 part from the dealer but it took the dealer 6 hours to find the problem. good luck.


Disconnect your battery for 30 seconds, the code will clear, the light will go off. See if it stays off.


p0440 is a EVAP malfunction. I did erase the code and double checked the gas cap. The same error code was generated again.


That i swhat I am going to check next. Like I said the error code was genrated after teh Sender unit was replaced because it had a gas leak. I took it back and teh guy double checked the work he did and wanted a lot of moneyto trouble shoot the error code. I said I did not have thi sissue before I brought the car into you… Auto service centers are getting to be rip off salons for vehicles. Really.


You said that the fuel sender was replaced because it was leaking fuel.
If the gas tank was leaking fuel the code should have set. If fuel leaks out it is not a sealed system therefore you have an evap leak.
Now you want to blame the mechanic and call him a rip-off artist.
Is the fuel leak fixed?
Did you buy a cheap aftermarket gas cap?
How long has the check engine light been on?
Who is checking the codes?
How long was it leaking fuel?
Some things don’t add up.


A lot of talk about cheap replacement gas caps. My Sienna shop manual even says to check for genuine Toyota gas cap as part of the 0440 troubleshooting.

Well, we will see. About a month ago, I got a 0440, and went to the dealer and bought a new cap, cost quite a bit.

I drove around the country as is my wont, total around 4,000 miles with no further problems.

When I got back to Texas, I got a 0440. I fiddled with gas cap, erased it, and it went away for a few days. Next time I bought gas, it waited a couple days, and there it was again. Fiddle with gas cap, erase it, and it is okay until I buy gas, then a couple days later it comes on again.

I would say it is close to 8 or 10 ‘trips’ when it fails each time, and I think the code is 2-trip failure.

Today, I went to Advanced Auto parts, and paid $7 for a replacement cap. Purely experimental action on my part. I am convinced if the failure does not come back, it will have been a marginal new Toyota gas cap. If it does come back, there will be some flaky failure in the other areas mentioned, since it waits so long to fail each time – in fact, until after I buy gas again.

My experience over the years is if you have a difficult problem, but especially if it involves different mechanics (in my case due to a lot of travel), each and every one will replace the same exact parts that have been replaced before, at great expense to ME, no matter how good the parts put in were and no matter how short a time.

So, my belief is if I take this to Toyota, the very first thing they will do – especially if erasing it fixes it for a few days – is replace the gas cap again, at my expense. So, I might as well do it myself.


P0440 indicates a leak in the EVAP system. It does not indicate a faulty gas cap (although a faulty cap may be the cause). I find it hard to believe that your vehicle was leaking fuel and needed a sending unit and the check engine light was not on. If fuel can leak from the system then vapor can leak as well. If you have a vapor leak you have a check engine light.
So again how long was the light on?
Did the mechanic change the sending unit or the O-ring?
Does it still leak fuel?
How are you checking codes?


on the outside:

i am just making a suggestion here.

when replacing the fuel tank sensor if they dropped the tank (although i am unsure if that is necessary) did they re seat the fill tube gasket, to make the vapor tight connection? that would give the same error code as a loose gas cap


P0440 indicates a leak in the EVAP system. It does not indicate a faulty gas cap (although a faulty cap may be the cause). I find it hard to believe that your vehicle was leaking fuel and needed a sending unit and the check engine light was not on.

When I took my car in to get it inspected it did not pass because the car had a gas leak. It was determined that the leak was from the fuel pump sender unit gas line going to the engine. At that point what could you do???

If fuel can leak from the system then vapor can leak as well. If you have a vapor leak you have a check engine light.

All I could say is you are welcome to take it up with the garage that did the work. $560 plus dollars later they dropped the tank and replaced the sender unit, O ring, and put the tank back.

So again how long was the light on?

When I come down on auto mechanics I have good reason for doing so. Before I brought the car in I had just put $15 dollars worth of gas in the tank. It amounted to just under a quarter tank actually. When I picked the car up the gas needle was in the red zone?. Like what happened to the gas I put in the tank??? I began to drive the car home and the engine stalled several times and the gas gauge dropped to read E!!! I said to myself a few choice words and to make a long story short the garage ended up towing the vehicle back and fixing the problem. The mechanic did not properly put the gas line clamp back on after he checked the fuel pump pressure. Gas was pouting out of the engine compartment where the front wheel hub is?.. I told the numb nut behind the counter you people are lucky there was no engine compartment fire where the car would have been a total loss?.. No reply??. I get in the car and no gas!!! They could have put in a quarter tank of fuel after inconveniencing me for two days.

The light went on about 1 day of driving it and remained on for a good week.

Did the mechanic change the sending unit or the O-ring?
Does it still leak fuel?

He did change the O-ring and the complete sending unit.

No fuel leaks that I could tell.

How are you checking codes?

Handheld OBD II reader. I know it is not a multi thousand-dollar unit but it sees the code the same as a more expensive unit does. I also know that the returned code does not necessarily mean it may be that problem. It only means that is what the computer is seeing.

I erased the code and drove the car some more. The check engine light came back on so I called the garage and said you need to look at the car again because the check engine light came on after you people worked on the fuel system.

The mechanic pressure tested the tank and said there was no problem with what he worked on. He then said we could check the entire system for you but you will have to pay for it. $89.00 I was not going to have him work on it again?. They should have pin pointed the issue because the problem was not there when I brought he car in.

This is not the first time I had issues with car mechanics?.. They do things fast and not always properly but they see nothing wrong in getting that $70 -$100 per hour labor rate!


When I took the car back to teh mechanic he checked the tank for possble leaks by pressure testing it.
The whoel thing is odd… I am not saying they did anything intentially to the mechanics of teh vehicle but I feel that they shoudl pin point the issue out as it happened right after they worked on the system of the vehicle…


Well after a response like that you can forget any help from me. Good luck fixing your car. I now understand why the repair shop doesn’t want to deal with you.


Michael lets be clear on something. You were not helping. you were guessing and you were assuming things that were not true or incomplete after all the pertant information was given. If you did not like the remark about the auto mechanics well, if I had a good one I would not be having this issue.


Yes lets be clear. Show me this guess work on my part.
At this point all I did was make comments about the operation of the EVAP system and ask questions regarding what has been being done to your vehicle.
After 20+ years as a certified tech the last 7 running my own shop I have found that guessing is not a valid option. It is much easier to explain to the customer how things work and ask as many questions as possible to determine where the problem might be.
I do not assume that because an evap light is on the gas cap is the problem. I want to know if the customer has changed it, when, where the part came from, etc… This eliminates the need to replace the same part multiple times.