I have a 2003 Honda Civic with slightly over 90,000 miles (I know, I commute far which is why I got the hybrid). About 1,500 miles or so ago, my engine malfunction light came on (not the one for the oil change). I took it into my local dealership and they told me that my cat converter was bad. They said that I'd need to get it fixed, but not necessarily right away.
Well, ever since that light went on, my fuel efficiency has plummeted. I was getting over 50 MPG regularly during my 58 mi/way trips to work. Now, I'm lucky if I get 40 to 42 MPG. Since purchasing the car in July 2003, I've averaged 49 MPG overall. Its now sliding down to 47 MPG.
Has ANYONE ever experienced this problem, had their cat converter go on them at 85-90,000 miles, or anything remotely similar? I am perplexed. Clearly, something is wrong. The dealership wants $1,000 to replace the converter, $950 or so for the part alone.
Any suggestions would be welcomed. Thanks.

Well, the obvious suggestion is to have the cat converter replaced. When they go bad, it screws up the emmissions system, which can do all sorts of funky things for your milage.

I agree, replacing the CAT is probably the solution.
Consider other places for this service, as I've read many stories (here) about factory CATS failing every 50 to 90K on the HCH1 cars. Plenty of folks will say that the aftermarket CATS will fail at 50K or so. Some do, others don't. It often depended on the brand. And at (probably) about half the Honda price, it would be worth rolling the dice for me.
Be sure to check out lots of shops, and ASK what kind of cat they are using. There are poor generic ones out there (specific brands, even, that many of these shops arewell aware of). Try a true muffler shop. I'm not recommending Midas, per se (and I've have issues with them in the past). Prices vary wildly, sometimes for the exact same parts, that's why it pays to find out EXACTLY what brand and type of CAT they would use. I eve nget a part number if I can.
On my old Jaguar, the prices ranged from $1200+ down to $400. For one particular CAT part number, 3 different shop prices (including labor) were $400, $580, and $725!

Another option is to find the factory part cheaper (collegehillshondaparts.com or the like). I just searched their site and found:
Part Number Description Year Model List Price Our Price
18160-PZA-A00 CONVERTER 2003 CIVIC 950.41 741.32
18190-PZA-A00 CONVERTER 2003 CIVIC 890.76 694.80

Not sure if that's a front and a rear converter (probably so), but the $950 list priced-one sounds like your part. There, $200 bucks saved.

BTW folks - none listed there yet for the HCH2.

Steve

STOP terrorism - Drive a HYBRID

Vehicles:
350 miles a week ------------ 2006 HCH II, Magnetic Pearl, w/NAVI (born on May 25, 2006)
350 miles a month ---------- 2003 Mazda Tribute ES-V6
350 miles a year (for now) - 1986 Mercedes 560SL

It seems odd that it would fail so early since you are passing so little unburned hydrocarbon thru it at 50 mpg.
O2 sensors fail more commonly that cat cons. I would invest in a code reader(or a scan guage) and double check to make sure that it is actually the cat con.Heck, in some states they are in warranty until 150,000 miles.Have you checked the warranty?
Get a code reader-or borrow from autozone etc-.Luck,Charlie

I would get a second opinion - and have the code read and reset.

After the reset, see if the code reappears. The ECM may be in limp home model - open loop and not closed loop with the O2 sensor(s).

Greetings!

I have a 2003 HCH and its CAT failed at 45k and 90k. The FE does decrease a bit after a CAT failure. The good news is that Honda *knows* that the 2003 HCH has this problem. If you call Honda's customer relations line, they will authorize the dealer to replace the CAT for free.