# P0300 When Gas Tank Not Full



## SirBreaksAlot (Aug 3, 2013)

Is there something that could be related to the fuel pump or some kind of return or vacuum line related to the gas tank that could be acting up when the gas tank level falls below completely full and air fills the void?

A little history to answer most of the normal questions:

I have an '01 Sentra 1.8L with 150K that only drives about 8 miles a day and usually only has a little gas in it. For a while I've had a P0300 code (along with the fix-it light) and every shop I have taken it to is stumped. Everyone is always looking at the engine.

Everything is new, ECU, plugs, coils, wet/dry tests where good, etc. All the shops said the engine and the components normally thought to be related to P0300 are all in great condition. The problem did not appear to be related to anything, it was so very random.

After my most recent try I thought maybe I had bad gas from the age and limited driving so I got a couple of cans of Seafoam. Ran the tank down added Seafoam and filled the tank, after about 16-20 cycles the fix-it light turned off. Once the gas gauge started moving south of the F, probably 3-4 days, the fix-it light turned back on.

After having a little come to Jesus talk with my car I ran the tank down again, added more Seafoam and filled the tank. After 16-20 cycles the fix-it light turned off again. Again the fix-it light turned on in the same manner when the gas gauge started moving south of the F.

I don't think the Seafoam had anything to do with it, I think it is related to the fuel level some how.

Thanks


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## rogoman (Dec 16, 2004)

A P0300 code could be caused by several factors such as:
- Improper spark plug
- Insufficient compression
- Incorrect fuel pressure
- EGR volume control valve
- Dirty injectors
- Intake system air leak
- Heated oxygen sensor 1
- Poor electrical connections

Keep the fuel tank topped out for several days to determine if the fuel level sensor is causing a problem.


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## SirBreaksAlot (Aug 3, 2013)

rogoman said:


> Keep the fuel tank topped out for several days to determine if the fuel level sensor is causing a problem.


I've already done this twice. A couple/few days after I top off the fuel tank the check engine light turns off. A couple/few days after that when the fuel level starts to drop and the gauge begins to show readings below the "F"ull mark the check engine lights turns on.

If it is the fuel level sensor, how does it cause this problem?

Are there any other situations you can think of that would be linked to the fuel level?

Thanks


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## worthirt (May 21, 2013)

It sounds like it may be poor electrical connections as stated by rogoman. Check them, make sure to check the grounds, when your fuel tank is full, it probaly is sending enough voltage to overcome the problems. I have a 94 sentra, it had a problem with my fuel sensor also. It was just really slow, I cleaned and regrounded the system and my problems went away, there were a few starting issues too. I had to change my battery cables to fix one of the grounds. You may just have a corroded cable.


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## SPEEDO (Jun 9, 2003)

bad gas cap or not seated?


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