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Old 03-05-2012, 12:28 PM
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Fuel Level affects Check Engine Light

My Wrangler periodically pops a check engine code for P0440, which is an evap leak detection.

I replaced the gas cap, which had no effect.

What does affect it is the fuel level. If I maintain 3/4 or more fuel in the tank, the check engine light cycles off and will stay off indefinitely. Also, if I keep 1/4 or less in the tank, it will cycle off and stay off indefinitely. The check engine light only comes on when the fuel tank is near 1/2 full. This is like clockwork. If I'm willing to do a fill-up every 140 miles or less, the CEL never comes on... The fill-up can be can be every day, or once a week. It matters not, so long as I don't dip below 5/8ths or so on the fuel gauge.

My Wrangler also has the gas-burp issue with the inlet check valve (ICV).

Has anyone else observed this??

The integrity of the suel system is the same regardless of fuel level in the tank. Either it leaks or it doesn't.

Could the bad ICV somehow be related to the P0440 code? My initial thinking is no, because the valve doesn't vent to the atmosphere.

However, I've inspected the whole fuel system and visually it's good. Given that there is no leak detected when full/empty, I can presume the solenoid and new fuel-cap are operating fine. A bad cap or solenoid would pop code 100% of the time. A cracked evap line or bad connection would also pop code 100% of the time.

This points me back at the ICV. Perhaps I'm only thinking the ICV is the root cause because I know it's faulty, AND I've read at least one post stating that a replacement ICV (which requires the entire tank be replaced) has eliminated P0440 for at least one member.

Do any informed Jeepers have a theory?
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Old 03-05-2012, 01:02 PM   #2
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I used to get that code on my 01 TJ. On mine, the fuel level didn't make a difference. I could never get it fixed. I had a few places tell me they think they found the leak, but light would always come back on. Supposedly the leak can be a millimeter and the light comes on. It never affected performance and I eventually just left it alone. Just had to disconnect the battery about a week b/f getting inspected.
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