My check engine light is on

[Undertoad]

The Cellar Car had the nerve, again, to simply stop acting wrong. The Check Engine light is still lit, but the engine is now running normally.

I believe the Cellar Car is self-healing.

[lumberjim]

Originally Posted by Undertoad

The Cellar Car had the nerve, again, to simply stop acting wrong. The Check Engine light is still lit, but the engine is now running normally.

I believe the Cellar Car is self-healing.

I had an '81 vw deisel rabbit that had that skill.


i can't remember what the hell happened to that car.....

it might still be out there somewhere .....

[tw]

Originally Posted by Undertoad

The Cellar Car had the nerve, again, to simply stop acting wrong. The Check Engine light is still lit, but the engine is now running normally.

That is how most all failures normally happen.

For example, a car with about 100,000 miles sometimes would knock during acceleration from idle. Dealer swore they could not repeat the problem. Eventually I isolated the problem to but a few parts, but could not see anything wrong. Well I took out the distributor (the #1 suspect) and disassembled it. Found grease that lubricated the centrifugal and vacuum advance was sticky. Have since learned this going 'sticky' can be a problem with lithium greases in ten years. Sometimes ignition timing would get stuck until heat or extended operation freed the part.

Finding failures means first using logic to minimize a problem to certain suspects. That is what the check engine light does.

For example, what could cause intermittent failure - without that check engine code and other important facts? ERG valve gets intermittently stuck. Fuel pump is slowly failing - pressure too low - so that sometimes the injectors cannot compensate for that low pressure. Filter partially clogged. Intermittent leak in critical vacuum line. Temperature measurement device is intermittent - not always reporting correct temperature. Device that measures air flow is intermittent. Sticky or worn injector. Oxygen sensor reporting incorrect values. Cracked distributor. Electronic load sensor fails. Any connector is corroded causing varying sensor inputs to the computer. Bad spark plug wire. Partial obstruction in the exhaust manifold. Atmospheric pressure sensor failure.

And this is maybe 2% of possible suspects. A list that becomes massively smaller with that diagnostic code or other symptoms. In every case, the part is constantly defective causing intermittent failures. The problem has not gone away. It is simply a classic intermittent.