02 Altima 2.5S Code P0031

Apparently this code is from a low voltage signal to 02 sensor 1. I changed the sensor and am still getting the same code. What would be the most likely cause of the P0031 low voltage error. This is an '02 Altima 4 cyl

Is the circuit okay!

I am not sure. How do you check it? I did manage to get a voltage reading off the input and it was very low, less than 1V. I checked all the fuses and found 1 blown, but switched it out and nothing changed.

First off, an o2 sensor signal is an input to the PCM, not an output TO the sensor. Secondly the voltage should fluctuate between.9 and .1 volts. This is it's normal operating range. O2s can stick intermittently, causing codes like that one.

The code is about the heat control circuit. How could that be an output from the sensor. To heat the sensor to 600F there would have to be an input to the sensor. The heater part of the sensor is just a huge resistor that gets hot. I think that is what the P0031 is describing.

Forgive me if I sound argumentative, that certainly is not the case. I am just trying to figure this thing out as I go. I don't want to end up getting fleeced by some dealer because of ignorance.

YEs, well you didn't post that it was the heater control circuit. You said low voltage signal to the o2 sensor. IN automotive terms the "signal" refers to the signal to the PCM from the sensor. Also the code you posted didn't sound familiar so I didn't look it up on my own. That's my first mistake.
So, to start over, if the heater circuit voltage is low, you'll need to unplug the sensor and with key on engine off(using a voltmeter) check for 12 volts at heater circuit feed. Is it there? if so, plug sensor back in and backprobe the connnector and see if you still have 12 volts. if so, you'll need to start checking the ground circuit for continuity. If you have no 12 volts at all with the connector unplugged, then check your appropriate fuses. Usually all heater circuits on one bank are fed off the same fuse, and sometimes ALL the heater circuits are fed off hte same fuse. So, if a blown fuse was the case you'd get multiple heater circuit codes, not just one. That said, usually heater circuit problems are because of a faulty circuit inside the sensor itself. Usually replacing appropriate sensor fixes it. Of course, you'd still need to check voltages to know for sure.

My bad. Thanks for the info. Replaced the fuse, no dice. Replaced sensor, no dice. I have no idea where the wires originate for the 02 sensor, and there is probably zero chance of tracing it. Unless the car starts running really badly, we may just have to live with the MIL on. But until I get totally fed up with looking and run completly out of options, the search continues.

All you have to do is jack up your car and roll under it and find the connector. Then do the above instructions. This is one of the easiest procedures to do.

I found the connection pretty easily when I changed the sensor. It is right up front and color coded to boot. The voltage was low before the sensor was plugged in so the fault must be in the wiring in the harness or the fuse connction I would think. Finding where the wires originate in the fuse panel or wiring harness to check the connection on that end I think would be nearly impossible.

well for someone who isn't a diagnostician it can seem pretty daunting. However, it's not really that bad

Maybe if I can narrow it down to that, and have to take it to a Pro, at least I will know if he's trying to pull one over on me. There are a lot of good mechanics and dealers out there, problem is I don't know any. Anybody got a good horse for sale? Lol Thanks for the time and help.

No problem, glad to help

HI

Are you sure the code number is correct ? Is it is referring to the heater circuit of the O2 ?

If the problem is in the heater circuit and you already changed your o2 sensor you will have to check the voltage supply. Are you sure your new O2 sensor is not faulty ? if it is on guarantee change it just to be sure it is not bad.
If the O2 sensor is ok then try these: Check the heater voltage supply in the harness wire, it has to have 12 volts only when you turn the ignition to on, the start your engine, at idle it has to have 12 volts, then start revving your engine, more a less at 3000- 4000 rpm the 12 volts have to dissapeared; if you are having at all rpms the same 12 volts then you have a voltage suply failure. Check the wires for shorted, dirty or broken also check the negative wire, check for proper ground if the negative supply wire is with a bad ground signal or broken it could make a bad grounding voltage in the sensor.

He posted that he had low or no voltage with the sensor unplugged. Then I directed him to do some tests to find the source of the problem .

Why would the 12V go away at 3000-4000 rpm? This does not make sense to me. I don't have 12V but if I did, why would it go away at 3-4k rpm and not when the sensor was up to temp?