How to read check engine light error on 1991 Civic
 

Can you point me to the post/thread with the instruction to retrieve the error code on a 1991 Civic, 1.5L engine.

The engine check light came on intermittently on my Civic for about a month now. The gas mileage has dropped to 30mpg from 34mpg. I couldn't tell the difference in performance at all. The gas mileage difference and the check light are the only evidences that something is not going right. Where do I begin? What should I look for?

Thank you in advance.

Thank you very much RonJ. I will check it out.

I just read the error code. Luckily it's only a single error, according to the above table posted by RonJ, it is:

Code 1: Oxygen content (with CATA), page 6-154.

Where can I find page 6-154 (and 6-155)? And more importantly what is the fix for this problem, based on your past experience? Many thanks in advance.

Here's what I observe on my 91 Civic: The light is NOT on when I started the car. It came on and stayed on after about 30 mins driving. When I turned off the engine and turned it back on, the light is not on. Then the cycle repeated itself.

Almost certainly, the oxygen sensor is bad. It's screwed into the exhaust manifold on the front of the engine.

I think I might have found the problem. A frayed leaking vacumm hose.

How do I reset the ECU to get rid of the error? Thanks.

Can I assume the vacuum hose was attached to the fuel pressure regulator?

Reset the ECU by removing the 10A Hazard fuse in the main fuse box for a few minutes.

I don't know. I will look. Thanks for your help.

RonJ,

I just looked and I still don't know if it's attached to the fuel pressure regulator. In fact, I could not positively identify the fuel pressure regulator.

Anyway, it's the big (1 inch diameter) inverted L-shape (about 6 inches long) that connects the black PGM-FI box to the input header on the driver side.

I have cleared the error code as you instructed. Hopefully the light will not come back. Thanks.

That hose directs filtered air into the IACV valve for idling. It would not cause a code, but it would allow dust into the engine so it needs to be fixed.

The fuel presure regulator is on the driver's side of the throttle body it has a small hose which I think goes to a valve on the firewall. The large hose to the firewall returns fuel to the gas tank.

mk378,

You are right. That was not the cause of the check light. The light came back within 20 mins of driving. So I do I verify that the oxygen sensor is bad? Does a bad oxygen sensor results in worse mileage?

Thanks