Cel Light On And Off.

[synikal1022]

I have a weird problem that pops up every now and then, first let me tell you about my car.......1998 ls400....136k miles....very well maintained....oil changes every 3k.....runs great!....gets 25-26 combined MPG....only use Chevron premium fuel. The issue is the CEL comes on only when my fuel tank is less than 1/2 full, once I fill it back up light goes off within 10mins. I thought it might be the gas cap but that was replaced and issue still there. My son and I scanned the car and it shows catalytic inefficiency, if I remember correctly the code was P0020 or P0200. It makes no sense to me that the light goes on and off depending on fuel level and I cant relate fuel level to one of the cats being bad.......Any input would be greatly appreciated.

[billydpowell]

I have a weird problem that pops up every now and then...... yes you do.

NEVER heard of that one..... maybe someone has..

I am in agreement with you.

[synikal1022]

Hope one of the experts on this forum can shed some light on my issue......today as I was driving I again noticed that the CEL light came on and my tank is a little less than half full.

[AndyLowe]

Hope one of the experts on this forum can shed some light on my issue......today as I was driving I again noticed that the CEL light came on and my tank is a little less than half full.

I'm certainly no expert, but it appears to be a Fuel Vapor Solenoid, Vacuum Hose relationship. There is a solenoid valve at the lower edge of the driver's inner fender, and it is commanded by the ECM. It's purpose is to route fuel vapors from the gas tank, to the Intake Manifold, to be burned rather than released to the atmosphere. There is a rubber hose that connects the solenoid valve to the Intake Manifold and it often breaks on it's underside, right at the bend, where it connects to the intake manifold on top center forward area of engine. Check this hose for a break or split on each end. If the hose was broken, it would add too much air and be a contributor to a lean condition, when the ECM program is expecting a more rich reaction, having commanded the solenoid to add some gasoline vapor. This could cause the catalyst too lean/inefficient code you are receiving.

Hope this helps!

Andy

[synikal1022]

Thanks for your input, Andy. I will make sure and follow your instructions and hope that it solves the issue.

[VBdenny]

My Nissan pickup does the same thing. When it gets annoying, I dump a bottle or two of Complete Fuel System cleaner in the tank before I fill up. Pretty lazy way to fix it but it shut the light off and it stayed off except for when I bought some Royal Farms gas and it came on for awhile.

[lexfourcam]

i have a similar problem and ive had it for a while. my car has absolutely hardly any power, and is throwing one codes rpm no.2. the car was recently put back on time so i know it can't be the timing. ONE of the cam sensors was replaced, new fuel filter, spark plugs wires, O2 sensors in the exhaust manifold. I was being told because i removed the catalytic converters the car would run like crap because the O2 sensors after the cats. Is this true? the car is a 94, and i never had any problems until i put the headers and cat back exhaust system on. The other website told me that there was no check engine light for the O2 sensors after the cats so would this cause it to throw another code?