[gcree20]

Car: 2003 Spec-v

I know there are dozens of threads on these codes but after reading all of them, I still have no idea what to do to get rid of these codes. As with everyone, it all started after I replaced the header with a catless one. The new header only had 1 o2 bung, something I didn't realize when I first ordered it. Since it is stainless steel they could not weld a second bung on. I decided it would be easiest to order an o2 sim so I got one and soldered it in there. I reset the codes and the SES stayed off for months. Then last winter while I was doing a coolant flush, the lower o2 sensor wire somehow came loose and fell into the radiator fan. I got it out of there right away and there wasn't much damage to the o2 sensor. The white sheath that protects the wires was a bit chewed up in one place but none of the wires underneath had been damaged. Even still, once I went to start the car the SES light was on and the codes were P0031 and P0037.

I decided to ignore it for a long time as the car drives fine and it really isn't a big issue but I am planning on selling the car soon and I think it would be easier to sell if the SES light was off. I took it down to an exhaust shop today and had them weld an o2 bung behind the main cat under the car. They installed a new NTK lower o2 sensor in the new bung and extended the wires, thus getting rid of the old o2 sensor and the o2 sim I had in there. I watched them do it and the wiring looked good when they did it. I checked it again afterwards and it looks like everything is connected right. I cleared the codes but within a few minutes the SES light was back on. I checked the codes and it is still the P0031 and P0037 codes! Sorry for the long post but if someone could tell me how to get rid of these codes, I would be very grateful. Thank you!

 

[i68k]

P0037 NISSAN - HO2S12 Heater Control Circuit Low
P0031 NISSAN - HO2S11 Heater Control Circuit Low

the 04+ headers have one o2 bung and the 02-03 headers have two o2 bungs. i guess you got the wrong year header? and you can weld stainless, maybe you went to the wrong mechanic? im not sure why you welded the 2nd bung under the car where you had to extend wires, but at least you soldered those voltage specific wires

considering you had an o2 sim, and your occurance, its possible the fan caught the wire and yanked the wires cause them to break internally, or break contacts in the box. the previous problem, while you had o2 sim installed, seemed to be your primary o2 was failing and the o2 sim just replicated the signal for the lower o2, ie the reason both sensors have low readings. have you changed your primary o2 sensor after you installed your new lower o2 sensor? in the fsm are voltage&ohm readings for hot and cold o2 sensors.

double check your battery terminals for tightness and good contact, check your battery voltage motor on&off, this would be another reason for low readings.

 

[gcree20]

Thanks for the reply. I was following the advice in this thread: http://www.b15sentra.net/forums/showthread.php?t=135241 and was under the impression that moving the o2 sensor behind the main cat was the only option I had left. I should add that when I first put in the header I got the usual code, P0420 I think it was. It wasn't until the fan incident that I got the P0031 and P0037 codes. I haven't replaced the upper o2 sensor. I figured it was fine since I hadn't done anything to it and it wasn't the one that got sucked into the fan. I guess replacing it is the only thing left to do at this point.

You could be right about the fan incident messing up the wires. Is it possible that it could have broken wires in the wiring harness itself so replacing the o2 sensors would not fix the problem? In that case how could that be fixed? The battery is fine although the negative cable is a bit loose because the nut holding it on is getting rounded.

 

[i68k]

Is it possible that it could have broken wires in the wiring harness itself so replacing the o2 sensors would not fix the problem? In that case how could that be fixed? The battery is fine although the negative cable is a bit loose because the nut holding it on is getting rounded.

you are correct, the wire couldve broken up beyond the connector, in the harness. if this is the case, you should follow the troubleshooting in the fsm, it will show you what wires/pins to test, so you can determine where there is a break in the wiring.

like said previously, it's possible your upper/primary o2 sensor is failing, maybe caked up or it's transitioning slower than the ecu can adjust to it. the primary o2 controls your a/f ratio, essentially how the motor runs. the second o2 is generally emission, which diagnoses the primary o2 as well.

if you havent gotten a primary o2 sensor, i would get an ntk sensor with a connector and the 2 anti-foulers for the lower o2 sensor. but for starters, get a terminal or new ground cable for your battery before your voltages are skewed, ie your o2 sensor readings, and make sure the battery is getting good ground contact.