Why would CEL go out by itself?

[PAExplorerXLT]

My CEL which was on for an issue with the O2 sensor was on for a day then mysteriously turned off today. It has done it before. What is the reason?

 

[koda2000]

because you have intermittent problem.

 

[MAS Tequila]

Mine will do that occasionally if I run the tank extremely low or get a tank of bad gas.

I'll fill up with the non-ethanol and 20 miles later it goes out.

MT

 

[drdoom]

Don't worry it will be back.

 

[PAExplorerXLT]

Don't worry it will be back.

No kidding. It has done it before. I really question some of these so called engine monitoring systems. Rarely do they point you to the exact source. The biggest bugaboo of old cars is the check engine light. Nobody can figure them out.

 

[drdoom]

Yes I will agree to a certain extent that OBD can by it's very nature be somewhat cryptic. This is where you need to take your diagnostics further, using a multimeter and test light. Most sensors have a simple test protocol, on the vehicle or workbench too. For instance your O2 sensors can be probed with a meter, monitored on a laptop or smartphone, or bench tested with a propane torch. Once you wrap your head around it a bit, and start with the simple and free, you will eventually start to win, and save some serious cash. It's not always the sensor or module, not always the wiring or plugs, or vacuum. We all learned the hard way, and still are, every single day.
YMMV

 

[PAExplorerXLT]

It's not always the sensor or module, not always the wiring or plugs, or vacuum. We all learned the hard way, and still are, every single day.
YMMV

That's precisely the problem. The P0153 code has half a dozen causes and it is not clear how you can troubleshoot them without going through each and every one of them. Take the catch all vacuum leak. Seems like it is the cause of every drivability problem but very hard to find. I have been told my problem may be the intake manifold gasket. This is not a small job to just go and give it a try. Even mechanics aren't so sure.

 

[BustedKnuckles24]

With the vacuum leaks, I believe you mean the P0171 and P0174 codes. I chased those with my 2000 Limited for nearly a year. I checked everything, from vacuum lines to fuel pressure. Finally decidd to tackle the intake manifold gaskets and did both upper and lower so I wouldn't have to do the job twice. Gaskets were only $20-some-odd, and a couple of hours on a Saturday morning. Solved my problem completely. Wish I could say the same when the thermostat housing blew.