SES light for O2 sensor Bank 2 sensor 1, now sensor 2?

[Korben15]

Hi all. I have a 2006 M35. I was getting code P2A03, showing that the Bank 2, sensor 1 oxygen sensor voltage was off or something. Replaced that o2 sensor and everything was running fine. Now a few hundred miles later, I'm getting code P0157 for bank 2, sensor 2. It is extremely unusual for o2 sensors to go bad I've heard, is there any other reason that this would be happening? Thanks.

David

[Ilya]

It's actually pretty common once the car approaches or passes 100kmi. How many miles on your car?

[Korben15]

Common for both to go bad about the same time? 165,000

[Korben15]

It's actually pretty common once the car approaches or passes 100kmi. How many miles on your car?

The plot thickens. This morning I got into Bessie to go to work and the SES light was off. If the o2 sensors aren't giving the correct voltage, will it temporarily read correctly part of the time, and some of the time won't?

[Ilya]

Common for both to go bad about the same time? 165,000

They're both reading the same exhaust gases, so I would imagine that they could get clogged or too dirty to read properly around the same time. I usually replace mine at 100-110k regardless because by that time fuel mileage is probably starting to suffer a tad due to the sensors being warn down...but I've had them fail on my old Maxima around that time period. When one fails, the car starts running rich or lean which could foul the rest in theory if ran that way too long, not to mention the spark plugs as the car/ECU is thinking it has to give a different mix of air/fuel to keep the values proper (that's why mileage goes down when O2 sensors or spark plugs aren't working properly).

And yeah, at 165k, I would not be surprised if they all failed the same second to be honest. That's gettin up there, but nice to see your car is otherwise still running well. Gotta love that VQ .

It's actually pretty common once the car approaches or passes 100kmi. How many miles on your car?

The plot thickens. This morning I got into Bessie to go to work and the SES light was off. If the o2 sensors aren't giving the correct voltage, will it temporarily read correctly part of the time, and some of the time won't?

Yes, they are voltage dependent. If the ECU sees a lack of voltage, it'll trigger the CEL.

Did you clear the code earlier at all? Or how many miles did you drive since the CEL lit up? Usually it takes 75-100 miles (kind of guessing) to 'recycle' the OBDII tests (if you have a scanner you'll see what I'm talking about). If you only drove like 20, that is indeed interesting why the light went off. I'd keep an eye on it regardless.

Do you know what kind of mileage you're getting? An M35 should be around 18-19 if driving it hard and 20-21 if babying it IIRC from my car.

[Korben15]

I've gotten her up to 20.6 from when I bought it from my mom and she had it at 14.6. lol

[Ilya]

You'd have to monitor it over the course of a few gas tanks and don't use the computer (it's not exact). I can get mine up to 23-24 (V8 5.6L) for 20 minutes after filling up but then it plummets once I hit the rest of my area lol. To like 17.

On your next fillup, do the following:

1) Mark down mileage or reset one of the trip counters to zero
2) Fill up the gas tank
3) Drive until tank is almost empty, make note of the mileage on the trip counter
4) Fill up x number of gallons
5) Divide #3 by #4, that will give you your true MPG

Repeat this 3-4 times and then average the numbers out. And drive like you normally would, don't beat it (unless you do that daily like me lol) or granny it (unless you're one of those weird people that cruises with their blinker on in the left lane doing 10 under the limit ahahah).

I still wouldn't be surprised if all your O2 sensors started failing at 165k. That's likely more plausible than anything.