Oxygen Sensor P3255 - Regulation at Upper Limit

B6/7 S4/RS4
#1

Been a while since I’ve posted.

Got a P3255 code for “Regulation at Upper Limit” on the B1 S1 Oxygen sensor.

I know the obvious place to look would be to just replace the sensor, but was just curious if there could be any other low hanging fruit I should check first?

`
012885 - Oxygen (Lambda) Sensor B1 S1; Heating Circuit
P3255 - 001 - Regulation at Upper Limit - MIL ON
Freeze Frame:
Fault Status: 11100001
Fault Priority: 0
Fault Frequency: 2
Reset counter: 255
Mileage: 142152 km
Time Indication: 0

         Freeze Frame:
                RPM: 1937 /min
                Load: 20.0 %
                Speed: 51.0 km/h
                Temperature: 36.0°C
                Temperature: 21.0°C
                Absolute Pres.: 980.0 mbar
                Voltage: 13.970 V

000304 - Oxygen (Lambda) Sensor B1 S1
P0130 - 001 - Malfunction in Circuit - MIL ON
Freeze Frame:
Fault Status: 11100001
Fault Priority: 0
Fault Frequency: 2
Reset counter: 255
Mileage: 142153 km
Time Indication: 0

         Freeze Frame:
                RPM: 2235 /min
                Load: 27.4 %
                Speed: 85.0 km/h
                Temperature: 65.0°C
                Temperature: 21.0°C
                Absolute Pres.: 980.0 mbar
                Voltage: 13.716 V`
#2

Its a malfunction in circuit so it seems the sensor is malfunctioning. You can try clearling codes and see if it comes back right away. Sometimes you can get 02 codes and its just from a glitch on warm up or a signal interruption that trips a code. You have two frequency counts and it looks like they both happened in the same drive cycle so its worth a reset and see

#3

Cleared it a few times and it always came back.

Took it to the shop to get the sensor looked at. The sensor was swapped with a new one, but the same code appears.

Mechanic checked the circuits in the sensors and they appear fine.

He then did a visual check of the wires up the transmission and they appear fine.

One suggestion he made was to try and flash back to stock tune… is it worth trying?

#4

well the tune has nothing to do with this so that is a waste of time. I would understand if you just got tuned and this started happening but if you have been tuned for years with no issues that isnt going to fix anything.

if you swap the sensor with a new one is the code gone and comes back or no matter what you do with the sensor you still get a code… If that is the case then there is something wrong with the wire side of the car. just so I understand even if you put in a new sensor the code is still the same.

#5

That’s what I told the shop as well. It just didn’t seem likely to be the root cause after almost 4.5 years on the tune.

That’s correct, swapped the sensor with a brand new one (bosch), code still comes back.

I’ve asked the shop to fully check the wiring connections again for sanity since they only eyeballed it from the tranny upwards. I won’t get a chance to stop by until after work today.

I think this car could probably would have passed a tailpipe emissions test once the cats were warmed up.
This new scanning stuff is a pain.

#6

So all the wires were checked for continuity and they’re fine. Next step they’re gonna try swapping the harnesses to see if it changes sides. I also asked them to try another sensor or to flip them to see if the code travels too.

#7

No luck. Code remains on b1s1.

#8

This is a good idea. Basically plug in a sensor that you know has no codes or issues or plug in a sensor that the car should trip a code for. The fact that you replaced the sensors and you got the same code says there is something fishy going on. It might be ECU related as like the 02 driver has failed and its just going to get the same code no matter what you do. The coil pack and 02 drivers are in the ECU its possible those have failed.

#9

Tried unplugging the o2 and running and the code changed to open circuit, so the code isn’t “sticking” on the ecu.

So the circuitry and o2s appear to have been ruled out as far as I can tell.

I guess the next steps would be to probably re-flash the ecu and see what happens?

I hope it’s not the ecu hardware.

#10

Did you swap the harnesses… or try swapping plugs on sensors.

#11

So a new sensor was originally put in. Then since a code was still coming up I did ask them to try swapping sensors

Interesting twist - When I picked up the car I noticed that the code was actually different now. P2231 – 004 – Signal Shorted to Heater Circuit. Which seems to indicate faulty wiring or a short somewhere between the heater and signal wires, not the original code anymore.

So I then dropped it off at my regular shop that did all the other work on my car. They’re close to an emissions centre and they also have a flash cable if it comes down to it. My plates are almost expired so I’d rather have it somewhere where I won’t have to tow it around to get things done.

The did some checking and said the new O2 was bad, so another new one is on the way. Fingers crossed that this finally fixes it. The puzzling part is that the other shop said they had tried swapping the plugs already, which should have ruled out the O2 being bad?

#12

Well that should tell you just about everything there. If the new sensor is bad your going to be chaseing your tail on diagnosis. Sounds like it might just be as easy as the bad old and new 02

#13

Seems like I was chasing my tail. Another new o2 resolved it.

#14

It’s tough when you get bad parts right out of the box. That makes things very hard to work around and ends up taking quite a bit of time.

IMHO had the other shop actually plugged in one of the other sensors from the other banks like suggested. This would have been a much shorter proses for you.

Glad to see you fixed it. Thanks for updating the thread. Sorry it took so long to get