My service engine light is almost always on, it comes on at about half tank.When i had the code read it was an evap code, so i replaced my gas cap. After that it still stays on. Does anyone know what the problem is? Is this something that is common with blazers?

 

Do you have a body lift? If so, chances are your fuel filler extension needs to be tightened. If not, your gas cap could be bad.

 

No lift kit. I just have a stock blazer, no add-ons

 

The pressure sensor is at the top of the fuel tank (top of the fuel pump module) check for a loose electrical connection.

 

Yeah i have this same problem, so does my friend. The mechanic told me to check the fuel cap too but it seems to be ok. mine went off for about a day or so and then came back on.

 

did you clear the code with a scan tool or disconnect the batttery? also evap system is much more than just the gas cap. could be charcoal canister, a hole in the purge lines, or in my case it was the evap purge control solenoid.

ps. not topping of the fuel tank after it clicks automatically when you are filling up can help these evap probs. there is a reason the fuel pumps turn off, don't add that extra half gallon so you don't have to carry some coins in your pocket. parking your vehicle in the sun shortly afer more than filling up can push gas into the evap system which isn't designed to deal with liquids, but rather only gases ie. gas fumes

 

My service engine soon light came on over a year ago (96 Blazer). The mechanic at the local Chevy dealer said it was a broken evap valve and it would cost $175 to replace. I didn't have it fixed because I thought that I could get the part from an Auto Parts store and fix it myself. However, the parts stores in my town don't carry it. So I drove around for another year with black electricians covering the SES light. The broken valve obviously doesn't effect the truck's performance. This week I had the vehicle back in the garage toreplacethe fuel pump and had them replace the broken evap valve and clear the computer code to turn off the SES light. So far everything is O.K.

 

I just had P0440 today which is an EVAP code. I just cleared it and will see if it comes back again. More often than not, it is simply because the gas cap wasn't tightened properly or has gone bad. If it comes back, I'll try a new cap. If it comes back after that, it's the purge solenoid.

 

I am having the same problem. I got P0442 code. I just replaced my gas cap and want to see if that fixes the problem. Do you have to have a scan tool to clear the code, or are there any other ways?

 

The second time my light popped on, I just tightened the gas cap and let it go. In less than 1/2 a day, the light went away.