drew2

The car is throwing a check engine light and the diagnostics code comes up as something like "underperforming catalytic converter"

i read that the code can also be caused by the O2 sensor.

am i correct in understanding that this car has 2 o2 sensors, how do you know which one to replace?

BLKFLSH

If it is a code saying under performing cat. It must be the one after the cat. How would the one before the cat know how the cat is performing?

drew2

i should add the car has 198k and original cat/o2 sensor i believe

how would you attack this problem?

02 sensors are $80-100 for bosch i think
are the two o2 sensors different?

oem fit cat...around $150? where can you get a bolt-in for this car


i need to make this CEL go away before inspection

BLKFLSH

I think one of them has a heater, forget which one. It should have more wires than the other one. Hope that helps you. If you have a service manual you could check the sensor with a mutimeter. You could have a bad cat, can't say for sure. OEM is always better, in my opinion. You don't want to get a universal one and have to splice wires.

drew2

is there any way of testing the 02 sensor?

i dont have a manual and unfortunately i dont have any plan on buying one, this isn't my car.

the dealer read the code and said the cat needs replaced and another shop read it and said it could be the o2 sensors or the cat


is there ANY way for me to further diagnose this before throwing money at it?

BLKFLSH

Don't know how to test your sensor, sorry.

hondadude

Cat converter is a very common problem in your car..before this post gets out of hand and too many un-needed parts are replaced, the way to get a correct diagnose is to read the rear O2 sensor with a scan tool. Why would you believe the code is lying to you...if it says cat converter below threshold value....BELIEVE it!!
Replace the cat and get on with life

drew2

what??

i didn't say the code is lying to me. Im just tryign to do a proper diagnosis before i start replacing parts. If the car judges the cat condition by comparing the readings from the two 02 sensors, why is it improbable that the second o2 sensor is bad?


I'm not in denial, quite the opposite, im just making sure i do this right.

YeuEmMaiMai

you could have your emmissions tested that will tell you for sure where the problem is. The ECU thinks that the O2 sensor is within range due to the readings that it is getting from the sensor. the ECU looks at the data from the sensor and it can determine if the cat is working or not. With nearly 200K on the car, cat failure or O2 sensor failuire is not uncommon. expecially if you have gotten bad quality gas..........

Lowski

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. Your mileage is pretty high so something may actually be wrong, but who konws. Read on.

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 106,000 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.

To answer your previous questions...


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.


Chris

drew2

i replaced the 02 sensor downstream of the cat and 3,000 miles later the check engine light is off, the car also just passed emissions (no sniffer, just visual and code check)

Elvis1977

You eventially will have to replace the catalytic converter on your car. The light will probably come back on. I had to replace mine at 93k (98 accord 4-cyl.).