I have a vq35 '97, I initially had the Bosch o2 sensor from NAPA, that was in a Budget Y pipe, the front right one is in question, after a couple of weeks I got the damn 0503 code, I was like fine whatever let me get a new OEM one, so I got a new one from Nissan, and I replaced that when the cattman headers were installed, NOW the damn 0503 code is back! What the hell???

 

0503 oxygen sensor or circuit fault, right bank.

Check the circuit (wiring) for any faults or resistance issues. Make sure the connections are clean and secure. Spray some WD-40 onto the plugs or put a dab of conductive grease on each pin.

 

Sorry this has nothing to do with your question, but i noticed you lived in jersey. Where did you get your 3.5 installed? Ive been looking for a place that was close to ny to do it.

 

IIRC, Tilley did it for him

 

Gotta be the connections...

 

0503 - front right back o2 sensor.

Which o2 sensor have you been replacing? The one that is bad is the front o2 sensor in the y-pipe closest to the firewall, not the one closest to the radiator.

 

The last o2 sensor I got for my 99 from the dealer was also a bosch. That was the reason I went to the dealer, to get away from the bosch. But I got one anyway. No problems with it tho, It's been in for about 1500 miles and never a cel yet. (knock on wood)

 

Yeah I have replaced the front right o2 sensor, this would be the one closest to the firewall. I will try spraying WD-40 into the connectors.

 

Having same problem.

 

Did you check the fuse?

 

Harris, if you have not gotten this straightened out yet, you may have an issue where your headers/y-pipe removed a precat, and you are getting a CEL because your 2ndary 02 sensors are kicking an error w/o the precats. If this is the case, you could relocate your 2ndary o2's behind your main cat, or use an o2 sensor simulator.

 

figure out what it sends to the ecu and replace it with a resistor

 

check the exact code. it looks like your third one has gone