I replaced the 02 sensor about a month ago when I received the 0503 code months after replacing it with a brand new Bosch 02 sensor from Napa. Then I received the damn code again 3 weeks after replacing it with a OEM nissan! I resetted the computer and 1 week later it comes back again!!!!! I check the connector it looks good, it's on nice and tight, wtf????? This is expensive, and annoying!! HELP.

 

There are at least 3 O2 sensors on your car. Are you sure you're replacing the bad one? Also, it's good to check the connector but sometimes the wire themselves are bad or broken somewhere.

 

No such word in the english language. Didn't you have a thread up about this 2 weeks ago?

 

Bad ground.

 

Forgive me for not scoring a 4.0 on my org term paper. Yes I did have a thread and I replied I will reset the ECU and see if it comes back. Well, it did come back.

 

Bad ground? Where?

 

O2 sensor ground. Reground it, tap near the sensor and run a wire to the block or batt.

 

Umm forgive me for sounding like an idiot. But I'm lost. The O2 sensor as far as I know is plug and play. Screw it into the exhaust mani's and plug in the connector. Where is the actual o2 sensor ground located, are there seperate grounds for all 3 or just one main one?

 

I believe the ground goes to the Lower IM.

 

There are several engine grounding points on the car. Where does the ground on the lower IM which you are referring to track back to?

 

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Most of the sensors in the engine bay.

 

Your ECU may need to be re-programmed, the dealer will take about $90 to do that...Call and ask your Nissan dealer and tell them about the history of changing the sensors (talk to a service advisor of course)

 

I doubt that, if you mean re-setting it then I can do that myself within 30 seconds.

 

OH SH8! I think I replaced the wrong o2 in the first place. The front right is closest to the firewall DUH. I THINK I had replaced the one closest to the radiator, which according to courtesy parts is the FRONT LEFT. Can interchange the o2's to see if it's really the sensor that's bad?

 

Yes, you can.

 

If you look at your old thread, I believe I already suggested that you may be replacing the wrong sensor.

 

What are you talking about? The o2's are grounded to the heads via the exhaust manifold and/or the grounding straps attached to the exhaust.

 

Why does the FSM say to loosen and tighten the grounds on the lower IM when you are checking the O2 sensor then?

 

Not sure, but i do know these two things to be true:

1. The FSM makes no mention of a bad ground as a cause for an o2 sensor code.
2. The o2 sensor wiring harness doesn't include a ground wire. It's 2 heater wires and one signal wire. This means that the grounds that attach to the LIM have nothing to do with any o2 ground.

BTW, i just looked through the FSM and saw no instructions saying to mess with the LIM ground when checking o2's.

 

EC-144 on the 97FSM. But you are right. It is two heater and one signal. Woops. Sorry for the wrong info.