91 Civic with Code 1 problem
 

1991 1.5 Sedan, Automatic.
What else beside an oxygen sensor could cause a code 1? I am told that my symptons do not indicate the oxygen sensor.

Here they are. In the morning, the check engine light is not on. Around 10 minutes into the drive, the motor will run rough for around 5 seconds, then the check engine light comes on and the car smooths out and runs fine for the rest of the journey. Next time I start it, the sequence starts all over again. I have also noticed that my fuel economy has gone way down.

So any help would be greatly appreciated.
Thanks

Re: 91 Civic with Code 1 problem
 

The oxygen sensor signal yada does not kick in until right after warmup. The trouble starting at about 10 minutes (= right after warmup), the reduced fuel economy and the code all emphatically point to the oxygen sensor. It is not unusual for the bad running to not exist at all times after warmup.

Check the sensor wiring. Otherwise, replace it. A new OEM (= Denso) O2 sensor costs only about $30 total through Amazon. See www.densoproducts.com for the right Denso part number.

Re: 91 Civic with Code 1 problem
 

Hooray!!! I was getting ready to replace the oxygen sensor and found the wire broke. Maybe it got caught in the fan??? Anyway, I repaired the wire, reset the ECU and no more problem. Thanks for the Denso link. I am saving that one.

Re: 91 Civic with Code 1 problem
 

Hey cool. My 91 has a clip that keeps the wire far from the fan. Make sure you do not have a vandal for a neighbor, too. Cutting the O2 sensor wire and so messing over the Honda owner would be pretty darn easy. I think a person could even crawl under most Hondas c. 1990, reach up, and cut this wire, all in about two minutes.

Your post is particularly helpful for the archives, since most c. 1990 Civic enthusiasts know that a failing O2 sensor (as in old) will not necessarily throw a code but will exhibit poor performance (like lowered MPG). If one does get an O2 sensor code on an 88-91 Civic, like you did, chances are a wire has broken completely. I think this is the first time I have ever read of someone having the O2 sensor code on an 88-91. OTOH, many have benefitted from replacing their O2 sensor even when no code was thrown.