My Blazer has been showing the code P0440 on and off the past little while. It's fairly inconsistent, I generally make an effort to clear it every so often to see when it still triggers, I'm 95% sure its always at startup. I sometimes get a week or two without it going and some days when it triggers it will actually meet the requirements to clear the code on its own.

I've done the obvious and checked/replaced the gas cap (I actually lost it after this issue started) but it has not changed anything symptom wise. My fuel mileage is fairly consistent with where it was at prior to having this code pop up. The EVAP System is probably what I'm least confident diagnosing so I'm just wondering if there are some easy things I could check.

Also I side note I have been getting P0135 for my B1S1 o2 sensor. It as well is a little inconsistent however I do notice it it triggers after long uphill drives. I've logged the data with the OBD2 reader on my phone and can see the voltage dropping out as I reach the end of a climb. I have a new sensor on order but was wondering if this could this be related?

 

Bump, Issue still persists. Is there anywhere obvious I should start looking?

 

Do you fill the tank with the truck running. My son does it and I believe thats whats doing it.

 

I've never filled it running in the entire time I've owned it. I feel like it might be a small vacuum leak somewhere but find it odd it doesn't consistently trigger.

 

It's not going to do the evap tests unless all the prerequisite conditions are met. Fuel level and temperatures must be specifically met for the test to run. Maybe why is inconsistently set.

A P0135 being intermittently present could also intermittently keep the Evap test from running.

FWIW, I almost always fill mine up running. Never a problem.

read here

https://blazerforum.com/forum/diagno...plained-35145/

 

Thanks for the information. The O2 sensor will be replaced in a few days which I feel may be connected to this. Not sure if this is related but I only notice the 02 sensor triggers on uphill climbs.


That write up says thatIt definitely has gone those 3 trips and passed the test thus clearing the code. The system must still have some sort of integrity left if it's still able to pass the test.

 

I hate to bump this incredibly old thread I started but I finally fixed the issue all these years later. I ended up replacing all the vacuum lines on the vehicle while I was swapping out my trans that went this summer. After the replacement, the code hasn't been seen once and that replacement happened at the start of August. When we took the trans out a lot of the vacuum lines had cracks and were showing their age. Getting the vacuum system back up and 100% also fixed the weird issues I was having with my HVAC blend door changing the vents up.

Just goes to show I should have gone with my gut 3 years ago and checked into the vacuum lines more haha.

 

Thanks for the update! Atleast it wasnt bumped for something not needed lol