Thread: Bad gas cap caused car to fail Cali smog test

My brother took in his 97 b14 base for a smog test. Well it failed because the gas cap was faulty. His check engine light was on before he took it in, but I hooked up my obd2 code reader and reset the system before the test. Will a bad gas cap cause a check engine light? This really does make sense now. Smog guy said to get a new cap, drive the car on the freeway for 70 miles and if the light doesn't come back on we should be good to go. Oh yeah the check engine light is back on too.

yes a faulty gas cap will cause an evap code to throw, did you replace it with an oem gas cap or aftermarket, you may have to reset your monitors after resetting your MIL

Yes it is a evap code and the cap is not oem. Going to tell him to get a new oem cap. Will hooking up my obd2 code reader and hitting the erase button do the job? Or do I have to do something else to reset the monitors?

****ing A!! Ive been trying to diagnose an EVAP code for the LONGEST. Im going to change my cap.

If it turns out to be my cap then I am going to slap myself twice and apologize to my car.

sometimes the gas cap could just be loose.
another way to verify that it really is the gas cap, is to use a highlighter and mark around the gascap seal with it. tighten the gas cap and then remove it. look at the marks it left on the filler neck and if its not even you need to replace the gas cap.
also if your scanner can do and evap pressure test, you can just do that instead of driving 70 miles.

erase it then follow a very specific drive cycle

Drive Cycle to reset ECM: Sentra Forum / Infiniti G20 Forum / NX Forum: Nissan Forums / Infiniti Forums - NICOclub

follow to a T otherwise it wont set the monitors

Damn that looks like a task.
Thanks for the link klobbersaurus. I will pass the info to my bro.

How long does the oem gas cap last before it needs to be replaced?

Is this the same thing for sr20 b14's? Or is this only for the GA16DE? Nevermind. I read the thread again and it said "ALL MONITORS-ALL MODELS, ALL ENGINES"

yes, seen it all too many times when i worked at toyota. Either loose or bad was usually the culprit for the evap code that states something about fuel tank pressure. If its old enough it could be a leaking evap hose somewhere, ore a vac line to one of the solenoids is cracked or disconnected. Make sure they are all plugged in and tight.

We usually just check the gas cap first though. You will be surprised when we usually tell the ladies it was just the gas cap loose. haha. They always seem surprised. hahaha

On most new cars the fuel tanks are usually placed under a vacuum for emmissions purposes. i believe its to suck the fumes from the charcoal canister back into the tank when the solenoid is triggered open to do so. If the tank is not under vac the sensor will sense it and trigger the light. Its designed to be a completely sealed unit.