Does the CEL ever warn of impending doom?

[Earendil]

I know that there are many things that can, according to the documentation, trigger the CEL. However, I've only ever seen 1221, O2 sensor.

I recently spent a day at the track, where the CEL light insisted on being on the entire time. Of course, it only ever recorded 1221, but it worries me to run a car on track with the CEL light lit.

Has anyone ever had a well running engine throw a different CEL light, wherein you wished you had taken action based on that light sooner? Or do people generally ignore it as long as the engine continues to run strong and without noise?

[jlevie]

The light comes on for a reason and what ever issue it points at needs to be fixed. Sometimes what may look like a harmless malfunction may not be so harmless. In this case the fault code essentially says that the DME is not getting usable data from the O2 sensor (or maybe no data at all). That causes the DME to revert to open loop operation, which disables learned adaptive fuel trim. The engine is probably running rich, but it could be running lean. Neither of which is good for the engine. So immediate actions would be to install a new OE/OEM sensor and trouble shoot the problem is the fault returns after a DME reset.

[nando]

mostly, no. certainly a car with the dash lit up like a Christmas tree has issues that should be resolved, but a CEL doesn't mean pull over because your engine will explode. the things that would mean that are lack of oil pressure or high coolant temp.

I'd follow Jim's advice and fix whatever is causing your issue rather than continuing to ignore it though.

[Earendil]

I should have been more clear (for the 2nd time today) about the time frame in which I mean "take action". The situation I'm thinking of is being out on track with 15 minutes left in the session and the CEL comes on. Do you
A) Finish the session, then check the code
B) Slow the lap as much as is reasonable and pit at the next opportunity, then check the light.
C) Pull over at the closest turn station, check light, and deal with whatever you just set into motion with regards to track etiquette and rules.

I've been doing A), but wondered if anyone would advise B).

With regards to the 1221 code in particular and the car going into open loop mode because of it, it was my understanding that when at WOT the car is in open loop mode and ignoring the O2 sensor anyway. That said, I am looking into why the O2 sensor is being triggered.

[jlevie]

If the CEL is normally off, I'd say that heading for the pits immediately is the sane course of action. You don't know, at that point, why the CEL is on.

You are correct that at WOT the O2 sensor data is not being used. But learned adaptation when not at WOT is still being applied to the fuel maps. So it is still important that the O2 sensor be working properly to compensate for the normal variations in operation.

There is an exception to that. And that is when the car is dyno tuned with the DME reset (to clear adaptation) before every pull. You then rig the system to remove power from the DME every time the engine is shut off. There will be no opportunity for adaptation in the time between firing the engine and heading out on the recon lap.

[TobyB]

I've had a sense of impending doom all week-
and then my airbag light came on.

I fear it's your SRS light for doom,
Check Engine is just for the engine...

hee

t