primary o2 sensor problem

[harryhk]

Dear All:

Today, my check engine light is on. The error code says the primary o2 sensor is malfunction. I use a multimeter to check the voltage of the o2 sensor.

My car is honda accord 98 ex 4 cylinder.

After 2 minutes, the o2 sensor started to give the right voltage. ~0.35v. However, the heat resistance is always about 2k ohm. So I suspect that the heat resistance is an open circuit as according to the manual, it should be about 10 to 40 ohm.

But here is my question:
If only the heat resistance is broken, the o2 sensor should be working correctly after the engine has been run for a while. But my check engine light is always on no matter how long I drove my car.

Will a broken heat resistance make my check engine light on all the time?

Thanks a lot ,
harry.

[jgr7]

Yes and it will work right after the engine is warm. but you won't get rid of the light as long as the heated part is bad.
Jeff

[harryhk]

Thanks for the reply Jeff.

Today I look at the repair manual again and find out that even thought only the heat circuit is broken, the PCM will treat the entire o2 sensor as open loop. Then the PCM will use it's default value instead of the feedback from o2 sensor.

Is that true? If that's true, I should replace the o2 sensor asap.

Thanks,

[jeffcoslacker]

Most likely it sets open loop emissions operation until it sees engine coolant temps in normal range and legit values coming from the sensor...the whole point of the heated o2 sensors was that early ones didn't produce usable signals until at full running temp...so in the interest of being able to control emissions better even from a cold start, they began using heated o2 sensors to get the system into closed loop operation faster.

The reason your code doesn't go away is because once an emissions-related code is set, especially on cold start, it will have to see a certain number of re-starts and warm-up without the problem present before it would clear the code. Since the heater is out, it's gonna see it every time, hence the persistent light...

[harryhk]

Thanks a lot for the reply. I always get plenty of very helpful responses from the forum.

I am going to replace the o2 sensor. Hopefully the parts I bought match the original one. I will put my feedback here when I am done.

I just have two more not quite related question:
1. How to turn off the check engine light temporarily ? Some one says disconnect the battery for more than 15 minutes.
2. The time the CEL turned on is like 4 hours after I sprayed the "Prestone Belt Dressing" on my car pulley. I am not sure if those two are related. But on the Internet, the feedback of Belt dressing is very negative.

Thanks

[harryhk]

I replaced the o2 sensor today. The light went off.

Wish the problem solved. Some review on Amazon says that their CEL went back on after 3 days. Wish this won't happen to me.

Thanks guys for the valuable discussion.

[Tony Silva]

Originally Posted by harryhk

I replaced the o2 sensor today. The light went off.

Wish the problem solved. Some review on Amazon says that their CEL went back on after 3 days. Wish this won't happen to me.

Thanks guys for the valuable discussion.

I'm wishin' for ya

[danielsatur]

Yes, there's even a fuse for the H02 sensor.

Do a Google ''Honda drive cycle readiness'' , once you go through the drive cycle ASAP, your good.

[harryhk]

hey danielsatur:

Thanks for you reply. I drove to NJ couple of days ago after I fixed the O2 sensor. The CEL never went back. I think I am good now. I did google the drive cycle but I think it is not a problem in my case. When I replaced my o2 sensor and restart the car, the CEL went off immediately.

Thanks a lot for you guys. My car now runs very well. When I have this O2 sensor problem, my car engine will stall at idle speed sometimes. I did an experiment: I shift to parking, accelerate my car, then release the pedal and let the car running at idle speed. The engine will stop with 50% chance.

Now all those problems are gone. I am very happy.

[danielsatur]

Check and make sure you are getting good MPG, if good your car is also happy.

Make sure you replace the air filter + fuel filter.