My wife's '99 Accord EX 4cyl 5spd with about 92K on it had a check engine light come on. I took it to the local auto parts store and they said it was for "catalyst system below threshold" and suggested that I replace the (primary) O2 sensor.

I did some searching here and it appears that the problem is probably the secondary O2 sensor or the cat. That being said, I have a few questions.

1) I read something about an emmissions warranty extension in this thread:
https://honda-tech.com/zerothread?id=844730
but couldn't find any more info abou this. Does anyone know if this would apply to my car?

2) Is there an easy way to discern if it's the secondary O2 or the cat?

3) Should I clear the code and make sure the light comes back on before I worry about any of this?

Thanks in advance for any help!
Jonathan

 

The secondary O2 sensor's job is to report catalyst operation to the ECU. Either the O2 sensor isn't up to the job, or the cat converter isn't doing it's job. You could measure the O2 sensors activity, but I don't recall what values or cross counts to look for.

As for the warranty, typically emmission related components are covered under a Federaly required period of time that exceeds the basic manufacturer's warranty. If you have the owner's manual, it should be stated in there.

 

I posted something similiar earlier in this thread. (edited below)

https://honda-tech.com/zerothread?id=1475308


As long as the car is running fine without any loss in power or huel mileage I wouldn't waste your money on replacing the CAT and the 02 sensor.

Chris
--------------------------------------------------------------------------
I have had the same issue with my 1999 4 cyl. There are 1000+ threads out there covering the same issue. It seems that their is some sort of issue with this generation of Accords. The threads show that people replace the CAT only, sensors only or both. After all the rework they still seem to get stuck with the code again.

My first experience was around 80,000 miles when I got some cheap ARCO gas.(never again). Over the next 15,000 miles the code would come and go. There was no noticeable loss of power or gas mileage. I just kept reseting the CEL or leaving it be until it went away on it's own. I am currently at 107,000 miles and have been CEL free of this issue for over 10,000 miles now. I would say leave it be unless you see a drop in power or gas mileage.


O2 Sensors:

There are two. One in the exhaust manifold and one in the CAT itself.


Testing O2 sensors from the Haynes Manual:

Get a volt meter.

If you were to pull the connector of the O2 sensor off you will see 4 pins. With the external connector clip at the North posistion of a compass the following pins are in the following quadrants NW= SIG, NE= GND, SW = HTR, SE = B+ Volts.

With the O2 sensor connected, insert the + probe into the SIG pin and the - probe in the GND pin. Start the car. The voltage should be around 0.1-0.2 volts with the engine cold. After 2 minutes or so, the reading should start to fluctuate between 0.1-0.9 volts.

Tp check the heater you can place the probes on HTR and B+ Volts and it should read 10 to 40 ohms.

To see if the O2 sensor is getting power for the heater place the probes on the B+ volts and the GND of the car side plug. With the ingnition key on you should get a reading.

If it fails any of these tests, replace it. I personally have not tried the above, but good luck and be damn careful if you do.


Clearing Engine Codes:

Shut the car off. Pull the "Clock Back Up" fuse which is number 13 on the passenger side fuse panel for ten seconds. Reinstall.

 

Great information that I didn't find using the search feature. Thanks for taking the time to pass it along. In the meantime, I'll clear the code and keep an eye on my fuel mileage. If it keeps coming back I'll test the O2 sensor and let ya'll know what I find.

JR