zaezzz

Hello everyone.
Saw my first check engine light in the two years of owning the car. 102k miles 2004 e320.
Read the codes and there were three:
P0131 - pre cat bank 1 o2 sensor low voltage
P0141 - post cat bank 1 o2 sensor heater circuit malfunction
P0151 - pre cat bank 2 o2 sensor low voltage

My question is it likely for all three sensors to fail at once in a day? I find it odd.
Is there anything else that could have caused these codes to pop before i start replacing sensors?

//EDIT
Called one of my friends who is a mechanic at a BMW dealership and he said it may be the battery without me even mentioning anything about the battery.
Have had this problem for a few months with it, where if it sat for a day or two without being driven i would get a "Battery protection: Convenience functions temporary unavailable" warning that would go away after driving for about 10 minutes.
Could a dying battery lead to a failure in the O2 sensors readings?

//EDIT 2
Took the car out for a drive after 5-6 hours. CEL is gone. Will keep monitoring.

Thank you very much!

bbirdwell

You have approximately 32 distributed digital control modules in your car that constantly communicate with each other. Right up until the voltage drops too low and circuits begin to malfunction. You may want to remind yourself that your car is "brake-by-wire"; when the electrical system fails, so do your brakes.

Bring up the voltage on the instrument cluster (internet search). If under 12.1 at rest and engine off, check the main battery and replace if necessary.

zaezzz

HI bbirdwell.
Thank you for your response.

As for what is going on now. I went and bought a new battery about a month ago. Still kept on driving with the old one for about two weeks to take notes of the behavior of the car. The CEL would go on at random times, during a long drive, or a 100 ft after starting to drive, and not on every drive, maybe every third. It would sometimes go off when the car sat overnight, sometimes it would not.

I replaced the battery after two weeks, seemed fine for a couple of days and then it started again. CEL on after driving for 4-5 minutes, sometimes no CEL after driving the entire day.
Also the old battery was checked at Interstate, it was a little weak at startup dropping to 10.5V or so. The alternator performed fine holding the voltage at 14.0V-14.2V.

Called a friend of mine, will bite the bullet and replace all O2 sensors hoping it will solve the problem.
He is saying it may have started happening due to bad gasoline. I told him i filled up at arco a couple of times and he's saying it's probably due to that.
Time will tell, hoping for the best.

Thank you!

cetialpha5

If you're going to replace the O2 sensors, just replace the 2 pre cat ones. When the back two go, the cats are shot. Did you check the aux battery? There's also the battery control module.

zaezzz

I might just do that, thank you for the advice. Only 1 of the post cat are throwing a code.
Have not checked the aux battery. Might be a good idea.

Today i read the codes again after a CEL light, does not look too good:
P2082-08: Left 02 sensor, before cat : Short circuit in the signal line (P0151)
P200F-08: Right 02 sensor, before cat: Short circuit in the signal line (P0131)
P207F-01 Left 02 sensor, before cat: Aging, correction variable exceeded: Delay time too long (P2098)
P200C-01 Right 02 sensor, before cat: Aging, correction variable exceeded: Delay time too long (P2096)
P20C2-04 Right 02 sensor, after cat: Open circuit in sensor heater line (P0141)
P2009-08 Right 02 sensor, after cat: Heating capacity is too low(P0141)

I have this bad feeling that the person that replaced my engine mounts... after seeing him use a crowbar to push things around may have had something to do with this. Don't want to blame, but it's a feeling..
Have to leave now, will dig more later.

Thank all for your insights!

zaezzz

So the verdict is that i'm gonna replace all 4 O2 sensors. Checked live data from the right post cat sensor and the voltage shows a "biased" reading of 0.45V-0.5V no matter if idling or revving up. I have a very long trip coming up so just gonna bite the bullet and replace all of them, which is anyway recommended at 100k and i'm sitting at 103k now.
Will update once the sensors are replaced.

On a more positive note, a couple of weeks ago my radio started cutting out every 5-15 seconds for anywhere from 1-10 seconds. After digging for days and taking apart everything in my trunk i finally isolated the problem to the busted tele aid module which i ended up bypassing with one of those optical bypass loops. Radio now works great. Super happy!
Also, whilst taking apart my trunk i found the cause why my Dynamic seats where not working. The cause was a cracked hose going from the air pump to the air reservoir which i removed, shortened and plugged back in. The seats now work great as well.

Thank you all for your responses! Learned a lot about my car in this past week.

cetialpha5

As I mentioned earlier, just replace the front 2 and then see what's the story with the back 2. Normally the back 2 last the life of the car or the cats. They normally don't do much because if the cats are fine, they don't do much switching and they're not exposed to the exhaust before the cats. The front 2 are the ones that do all the work as they go up and down while the computer uses their inputs. When they get old and lazy, that's when they need to be replaced. The back 2 are supposed to be pretty steady because that means the cats are doing their job. If they followed the fronts, that means the cats are shot.

zaezzz

Trust me i would just replace the two in the front, but i'm moving cross country, a ~2000 miles trip, and i don't want to risk any surprises on the way. If the cat on bank 1 is shot and that's the reason for the post cat o2 sensor's malfunction, then i will know for certain that it is shot and that appears to be a very costly repair.

Thank you for your insights. Wish i had more time to replace them one by one.

ctravis595

anybody ever update their threads besides me? lol

zaezzz

Sorry, moved, got new job and totally forgot about updating.

Update: Got all 4 sensors replaced at a cost of 600$ in parts and labor. Engine light gone, made the trip without problems and car is still running fine after about 4000 miles.

ctravis595

Thanks for updating, thought it was strange multiple o2 sensors would fail all at once but hearing that it solved your issue makes me more comfortable in replacing all of them

edit: maybe I’ll start with the primaries

cetialpha5

Good idea. Many people just replace the upstream ones. The rears are only there to tell you if the cats are shot. Otherwise they don't really do anything.

zaezzz

And i would have done exactly that, but had to move from north to south in a day or two, so replaced all of them as to avoid surprises on the road.

sunnybenz45

$600! You could have gotten all the sensors for like $300 and put em in easy...

sunnybenz45

Did it fix your issue?