My car’s check engine light came on and the first thing I did was to RTFM. It told me to check the gas cap, to open it, release the pressure, tighten it, then to drive it for three cycles. I did, and the light went off. It seems to me that looking in the manual and finding out what it has to say should be the first step.
I realize you’re talking about catalytic converters, but these two lines out of context are hilarious. 
Really? My Fit is just one year newer, and it has an indicator specifically indicating the gas cap. I can’t remember if it’s a separate idiot light or if it spells it out in the display as it has only happened once several years ago, but it doesn’t trigger the check engine light.
My ranger has the same thing, and as far as I know it only lights under specific circumstances. E.g. If the system detects an evaporative emissions leak AND the measured fuel level has increased significantly, then it assumes loose gas cap and puts on that light. If the condition remains after successive key cycles, it’s then assumed to be an actual evap leak and the check engine light will turn on.
This.
Google “OBD2 bluetooth” to see a large choice of devices that plug into the OBD-II connector (found on every vehicle since around 1996) and allow its signals to be read by a smartphone app. They cost around $10.
One that works well is the Torque app - costs $5. It does a lot more than just display codes - it allows you to clear codes, monitor all sorts of functions while driving, etc.
The chance that this combo will not be worth $15 to any car owner is near zero. And you can be a hero by checking codes from the vehicles of your befuddled friends.
Check engine light will cause a car to automatically fail an inspection in my state, so this may not be an ideal solution. Getting hit with a fine for failing to get inspection or a ticket for driving with expired registration (registration won’t renew without a valid inspection) isn’t solved with a piece of masking tape.
I’ve read that due to auto shop pressure, you can’t get the freebie code scan at Auto Zone in California. 
So that might not be a universal option.
Mine comes on every once in a great while due to something loose in the exhaust system. A certain kind of bump will set it off.
I just pull the correct fuse for 20 seconds and it’s back to normal. Disconnecting the battery is overkill and has other consequences.
Note: I drive the car a bit after that if I have an inspection coming due. Their computer can see if it’s been reset quite recently.
Ugh, O2 sensor. $600, and needs to be ordered. 
I knew it could go from my last maintenance, but this really is bad timing.
Just checked out their site. You earned your commission.
Those Check Engine lights are also notoriously unreliable.
Mine came on once while I was driving down the road. I immediately pulled over and looked under the hood.
The engine was right there where it always is.
Stupid light.
Far be it from me to besmirch the reputation of what may be an excellent and trusted mechanic – I know nothing about your car and I’m not a mechanic or even a car guy – but just based on my own experience that sounds outrageous. IIRC it was something like $130 when I had mine done (I looked for the bill but couldn’t find it). But I think there are multiple different O2 sensors and obviously some may be harder to get to than others and may cost more, though IIRC most of the cost was labor.
More or less. But just to clarify, a drive cycle is a lot more than just cold engine to fully warm engine, or, looking at it another way, most of the non-continuous monitors require many different kinds of drive cycles before they complete. That’s why it’s usually a few days or more, and many miles, of highway driving, stop-and-go driving, cold starts, etc. before they all complete after fault codes have been cleared with a PCM reset.
On the last part, not “some” states, but all states and provinces AFAIK that use the OBD II system for emissions testing will fail (in fact, most won’t even do the test) if the requisite number of non-continuous monitors has not completed their drive cycles (you may be allowed one incomplete, or in some cases either two or zero, depending on the age of the car).
Same with the CEL (also called MIL, malfunction indicator light). If it’s on, they won’t even do the test. And if the light itself is defective, the PCM will still report “MIL commanded on” so automatic fail. Furthermore, over here, it’s an automatic fail if the MIL doesn’t turn on during the dashboard self-test, and then it has to turn off when the engine is running, AND “MIL commanded on” has to be “NO”. And then all the monitors have to report acceptable status.
I don’t think you have to get the O2 sensor fixed right away. It will affect your gas mileage if it doesn’t work, but you should be able to drive fine. You can probably wait until the timing is better for the expense if you need. Also, be sure to call around to see what other shops charge.
Cars need maintenance with use. And at specific mileage intervals. This is detailed in your owner’s manual.
You should expect and budget for car maintenance - new tires, oil change, etc. every so often.
With that said, check engine lights make it EASIER to find maintenance problems when they occur. The car is telling the mechanic what needs fixing/attention!
FYI - I regularly do the factory recommended maintenance on my vehicles and never get a check engine light!
You want to get it fixed sooner rather than later. If your O2 sensor has truly crapped out, your car will be reverting into a default fuel mixture, which will most likely be too rich, dumping unburned fuel vapors through your exhaust, ruining your catalytic converter. This can happen fairly quickly depending on how far off the default mixture.
Which O2 sensor is it? Did they say? I believe that this car has one before the catalytic converter and another one after. (the pre and the post cat 02 sensor.)
I can almost guarantee that the sensor can be had for less than $600 bucks. If you post the actual code and the engine your Civic has in it, I will try to find you one online cheaper.
Something else to check, though, is to make sure the thing is actually still plugged in and the wire hasn’t taken a hit or is resting right on the exhaust pipe or manifold, grounding out its signal. I have had both things happen to me as the result of running over a stick and the stick whamming the harness for the O2 sensor. I replaced it, but didn’t notice that the wire had flopped down and burned through the insulation and grounded itself out against the pipe. Its unlikely but its certainly worth a check.
FWIW I’m doing a generic search for 2000 Honda Civic O2 sensor and am pulling up $27.00 - $67.00 prices.
Heh, no, the price included labor. The part alone wasn’t $600. 
I just watched a short video on YouTube and it doesn’t look hard, though there may be more than one. The part seems to be cheap. $600 sounds rich.
Yeah, you need a better quote than $600. If you were nearby, I could do that for you for pizza and a 6-pack. And we could split the pizza and beer. That is less than 30 minutes of work on 90% of the cars out there. O2 sensor is stupid easy to do.
Here is a lady doing it herself.
For real, its super easy. Screw it out, screw the new one in, hook it up. Drink beer, scratch self.
Most of the time its very easy. Dunno where you are but if you are in the PDX area lemme know.
Sorry, don’t mean to blitzkrieg your thread here, but I just looked up something to confirm. Your car has two O2 sensors. One upstream (in the video in my earlier post) and one downstream. The one downstream is slightly more work, but only because it requires getting under the vehicle to do the swap. Still should not be more than an hour of labor charge.
Do you know which one is failing?
It’s super easy, if it comes out.
On the other hand, if it’s rusted in place, it could be tough to get out. That’s not a big deal if you have the right tools (in this case, jack stands if you need to get under the car, a good socket, lots of leverage, lots of PB blaster, and patience.) But without the right tools or sense, the OP could very well round off the corners of the sensor, or damage the threads, which means paying a mechanic extra to fix your mistakes.
If you have decent mechanical common sense and a little car repair experience, go ahead. But don’t start here for your first time DIY repair.
(After a few years of amateur car repairs in the rusty northeast, I’ve learned the hard way that I need to have a contingency plan for every single fastener that can be rounded off, broken off, or completely seized up… and telling my wife “get a ride from a co-worker” is not an acceptable contingency plan.)