Catalytic Converter false alarms on 99 Accord?

Hi All,

My wife has a '99 Accord LX with about 200K miles on it. She drives about 150 miles a day back and forth to work.

The check engine light has been on almost continually for the past 3 years or so. About two years ago, the shop told us it was the catalytic converter, so we had that replaced. The light came back on a month or two later, but we didn’t do anything right away. Since then, we’ve had the car into the shop (different shops) a few times, and they tell us that it is the catalytic converter–which we had replaced. When we tell them we had it replaced, they tell us that is what the code is showing.

So, my question is, is there anything on this car that could be failing and making the shops think it’s the catalytic converter? The only possible “symptom” that we are experiencing is that she gets much worse miliage than we expect from this car–in the 22 mpg range on the highway–but I have no idea if this is related.

It could possibly be an O2 sensor going out near the cat, they can trigger the code you’re getting.

Thanks for the reply, bscar!

I was actually thinking along the same lines, so I asked the technician if it could be the O2 sensor, and his reply was that the O2 sensor has its own codes. However, that does make more sense to me, because I find it hard to believe that we’d go through a second cat within three years.

Would the O2 sensor (or the cat for that matter) cause the poor miliage–or is that just my wife’s lead foot?

Thanks again,


That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Regarding warning lights:

  1. if the coolant temp light comes on, shut off the engine ASAP

  2. if the oil warning light comes on, shut off the engine ASAP

  3. if a FLASHING MIL/CEL comes on, shut off the engine ASAP

    ASAP means driving to the berm of the highway right now and not waiting for the next exit.

But if the MIL/CEL is not flashing, then it’s not an urgent indicator.

The codes from the engine computer are indicators. They indicate to the mechanic that a component CIRCUIT has incorrect electrical readings. The able mechanic then uses the codes as a guide of the components and circuits to test further. The codes, themselves, do NOT provide enough information to perform repair actions. The able mechanic uses the displays of a scan tool (and other analysers) to see the circuit and component (sensor or actuator) electrical performance. From this information, his knowledge and experience, analytical abilities, the able mechanic can decide on the next course of action. That action may, or may not, be a decision to change or repair something.

The question is, “Have you had able mechanics?”. I’m not convinced that you have. There seems to be a shortage.

There are several codes for each sensor, and actuator. You can get an auto parts store to pull those codes (free), and bring them here for advice.

Uncle Big Bob,
The answer to your question about the poor gas mileage and why the catalytic converter may become fouled, again, wasn’t given here. Did the “tech” tell you? Did he tell you how to stop it from happening again. Tell us, if you would like to know.

unfortunately the ‘code’ itself needs to be posted here. go to autozone and have them read for free.

post the actual code here. it will be in the form of: P0123 or close to that.

dont summarize, or abbreviate the code. don’t tell what the guys says the code means. post the actual code here.

and if there are multiple codes post them all.