(and, in my car - for one of many.. a 'lazy' O-2 sensor has one other effect: lower mileage.)

What I hear from those who pay waay too much attention to lots of car trivia, not just about their own: a non-revealing CE light is fairly common.

It's easiest to see with a scope; a 'dwell meter' + voltmeter will read the same information, but person has to 'see' via numbers, not the pretty picture. First test: you spray a whiff of starting fluid / lighter fluid into intake. See that sensor volts go to full 'Lean it Out' mode, "soon". Reverse test == pull off a small smog hose; too much air = lean extreme. Engine displeasure would verify that the ECU (engine control unit by-whatever-name) is actually reacting to sensor appropriately, of course.

(Alas, some mechanics do not really grok these feedback details to fullness ie. what the sensor signal ought to look like / that there Is such a thing as 'a lazy sensor'. No manual has a diagnostic code for this phenom.. that I've heard == it doesn't throw a code but can screw up mileage.)

Clever, logical diagnosis is handicapped by the fact of secrecy? / nonrevealing of either the algorithms in engine computers or even: the actual range-settings which trigger sensors. This makes it hard to insert test voltages or waveforms and vet the ECU.

Dealer manuals 'solve' this dearth of info in their testing flow chart$: "Replace ECU and run this test again". Hell for the Independent, natch - at least you can get these overpriced CPUs cheap on eBay or sorta cheaper from wreckers (who know the List price.)

An example of being led astray:
Knock, crank-timing sensor assembly was indicated by trouble code.
He replaced @ >$200 for parts + nontrivial labor.
Same CE error!

Turned out a bad bridge diode in alternator was sending spikes on the 12V (large enough that even the big capacitor/battery wasn't enough to filter.) Spikes triggered that particular 'bogus-fault'via the unsmart-ECU design.

Fixed alternator: all workee.
I Hate! that my ride has ~ a dozen undocumented $%&*#-computer black boxes. I sympathize with the mechanics, too - those who grok enough digital, still have to make up for such missing info.

Lastly.. with factory manual or other diagram: find the 'on-always'power fuse to the CPU which stores codes. Turns out that some, many? 'repairs' don't register until it IS manually reset / mem cleared. This is an easy first course for you, after you make any change, and before driving to test.


Luck..

One with fingers-crossed, making regular sacrifices to the Lectronics Small Gods.