I have a 2005 Civic Ex with around 75,000 miles on it. I just got the car a few months ago and everything seems to be great on the car. Just recently though the CEL came on and the codes were for Primamry O2 sensor and random misfire in all cylinders. There were 5 codes. I have read other places about people having this issue and trying to change a whole slew of things that never end up fixing the problem. Some people just give up and don't care.

The thing is I have increased my gas mileage from about 300 a tank around 25mpg to 450 a tank or 37 mpg. The only thing is the light. I assume and was told that my car is likely running lean. The temp gauge has not increased and there has been no noticable decrease in power or perfomance. It seems to transition into gears better and runs all around smoother. WTF?

Should I be concerned or just ignore it like was suggested to me?

 

It's running lean, which will make it burn hotter, which will eventually burn out the valves or worse. Replace that sensor immediately. Hondas are finicky about aftermarket sensors, go with OEM: http://www.hondapartscheap.com/south...t=0&quantity=0 Paying $225 is better than replacing the heads or engine.

 

Before he replaces the o2 sensor, he need to check to see if his exhaust manifold is cracked.. If it's cracked, he'll want to replace that as well before he replaces the o2 sensor. The manifolds like to crack right where the primary o2 sensor is and so that will affect the ground of the o2 sensor.

 

Well so much for better gas milage. I heard that taking out the o2 sensor could ruin the ehaust manifold any. I heard they like to stick and stip out due to the heat.

Would it be best to remove it and test the sensor? I don't feel like chasing a white rabbit and I heard the codes I am getting cause a lot of goose chases. I suppose the mpg increase is a giveaway.

When you mention cracked... I assume you mean a noticable crack along the insert hole. I also assume you are implying the sensor grounds out on the manifold, but the sensor has a ground wire so I am confused by your statement.

 

Thanks for the part link.

 

O2 sensors use the manifold itself as a ground for the signal.. When I said crack, yes an actual crack in the manifold itself.. The ground wires going into the o2 sensor is actually for the heater element, not for the o2 sensor signal, which is what is important. How else would a 1 wire o2 sensor work if it didn't use the manifold as a ground? They haven't changed o2 sensor designs (how they're wired), instead they've just tacked on ****, with the fundamentals being the same. Further more, I've confirmed this by actually testing an o2 sensor and having to probe one of the wires and probe the body of the sensor itself in order to get a signal from it. You can do this with a volt meter, a clamp and a butane torch and see how quickly the voltage changes.
http://www.youtube.com/watch?v=vdn4Dk5PSwc

 

By the way the CEL comes on immediatly when the car is started after resetting the ECU and it never goes out. I will try to get the codes up, but its p1300 series I think for random misfires and a sensor code, not sure if it's heat code or the other one. Can't recall. I will inspect the sensor look into ordering a new one. The dealer wanted $500 for replacing it and the said it ws the 02 sensor after I suggested it... I don't trust dealers... know to many people that worked at one.

 

Thanks for the info. Makes sense. I will definatly inspect the ground point.

 

If it's an EX then there is no sensor in the manifold. There's one on the downpipe right after the manifold though. But, yes, check for cracks.

On second thought, check for vacuum leaks also.

As to the code: The 1300 series deals with the knock sensor and cam sensor. Are you sure it was 1300 and not 300 series? If it's the 300 series you could still be looking at the knock sensor and cam sensor as well as the crank sensor. They all pretty much deal with interrupts of the sensor signals so it could just be a bad sensor or wire/connector on one of those sensors. Try to get the exact code and post it.