N54 Stock o2 faults

[E90fanatic335]

While I'm waiting to hear back from Chris on a possible tune, has anyone had a similar issue where the bank 2 o2 sensors keep throwing codes? I have replaced both the pre cat and post cat sensors and I still get temperature and function fault codes. I'm running the MHD 2+ tune with all the required upgrades done. The dealership agreed the o2 sensors were fine from insta D. I'm at the point where I either need to buy 300$ sensors again or replace the DME. I hope to just tune out this problem since my logs indicate the car is running fine. Anyone have a similar issue or any suggestions?

Thank you in advance

https://datazap.me/u/bimmerswagg/log-1527204096

 

[langsbr]

I would lean towards a wiring issue if the sensor has been replaced and is working. When I was having an o2 issue, I tried tracing the wiring and I believe the heater wiring is common between the two, so my thought would be a signal wire to the DME may not be secure.

Does the code pop up instantly, or after a certain amount of driving?

Also, save some $$ and get just the long wire sensor- it can be used in both spots, and it's only about $100 on Amazon.

 

[fmorelli]

First off what are the specific codes you are getting?

Not that you have this problem, but I was getting a heater error code, pre-cat. Ordered new pre-cat sensors. Took everything apart when the new sensors arrived. Turns out the bank 1 pre-cat plug was not plugged in all the way - the 02 sensor was fine in all functions, but I suspect the higher amperage on the heater line failed to make the jump. Pre-cat sensors from Bosch were $208 shipped for the pair from Rock Auto.

Filippo

 

[langsbr]

His screenshot shows 2ca7 and 2cab, both related to the heater. It may be as simple as yours with it not connected fully.

Don't overlook Amazon for car parts! The sensor is only 78 bucks shipped. I even broke down and bought an ac Delco one for 100 to see if my issue was sensor related.

 

[E90fanatic335]

My friend and I (BMW) mechanic found that the wiring from the DME to the sensor was cut slightly from someone forcing the engine cover over the wires. So we cut off that section of the harness which was only about an inch and used the BMW coupler to repair it. The issue did not change from before or after this fix.
Alittle about the history :
First the engine light was on for bank 2 sensor one so I bought and replaced it. Then the light came on for bank 2 sensor 2 so I replaced it. Now the light is back on for bank 2 sensor 1. I'm not sure what that means unless the first sensor truly is damaged again.
Are there any reliable bank 2 sensor 1 o2 sensors that you guys trust from Amazon or autozone?

 

[E90fanatic335]

The light comes on randomly. Sometimes after a week and sometimes after a day.

 

[E90fanatic335]

Just happened now which is about 3 days from clearing and resetting o2 regulations with MHD tool

 

[langsbr]

The 29f4 and 29f5 are secondary o2 codes, which I presume is from running catless downpipes. I would've thought the MHD 2+ tune would disable those, but it may be a checkbox you need to select.

Knowing you have a repaired wiring section, I'd be inclined to think that is still where the issue lies, or at least where I would focus my efforts at.

 

[E90fanatic335]

The 29f4 and 29f5 are secondary o2 codes, which I presume is from running catless downpipes. I would've thought the MHD 2+ tune would disable those, but it may be a checkbox you need to select.

Knowing you have a repaired wiring section, I'd be inclined to think that is still where the issue lies, or at least where I would focus my efforts at.

Those two codes are shadow codes that the MHD tune did correct. I think at this point I'll run all new wires from the o2 connector to the DME and carefully check the wiring diagram from BMW as I go. At that point if the error persists, I'll either have to replace the sensor or get someone to tune out that code for me.

 

[fmorelli]

How many miles? You didn't mention this but did you check the oxygen heater fuse in the glove box? I believe it is 30A Fuse #79 on an E90. Given cut wiring, I'd be inclined to do a continuity check on the wiring for that sensor. If none of this sorts it out, you could buy a spare Bosch sensor and plug it in just to rule out an issue with a defective sensor ... or you end up with a problem in the DME. I would highly recommend you read this thread for perspective, all the way to the last post (it is 2 pages).

Sorry to hear you're having this problem ... report back.

Filippo

 

[E90fanatic335]

How many miles? You didn't mention this but did you check the oxygen heater fuse in the glove box? I believe it is 30A Fuse #79 on an E90. Given cut wiring, I'd be inclined to do a continuity check on the wiring for that sensor. If none of this sorts it out, you could buy a spare Bosch sensor and plug it in just to rule out an issue with a defective sensor ... or you end up with a problem in the DME. I would highly recommend you read this thread for perspective, all the way to the last post (it is 2 pages).

Sorry to hear you're having this problem ... report back.

Filippo

View attachment 12751 View attachment 12752

The car had 70k on it when I bought it and now it has 89k. That's something I didn't think about. I'll check that fuse tonight when I get home, run the new wires and buy a spare sensor. I greatly appreciate all these ideas. And if it's the DME itself I'll just find someone to tune out those codes since I don't want to spend $2,000 on a DME.

 

[E90fanatic335]

The car had 70k on it when I bought it and now it has 89k. That's something I didn't think about. I'll check that fuse tonight when I get home, run the new wires and buy a spare sensor. I greatly appreciate all these ideas. And if it's the DME itself I'll just find someone to tune out those codes since I don't want to spend $2,000 on a DME.

I have heard of people getting their DME replaced with used ones that people cline but I would only really be comfortable with a new one that my friend can code to my car with Ista at the dealership. Also I have the 81 version in my car.

 

[langsbr]

Since the ISN has been hacked on the MSD80 and MSD81, a used ECU can be matched to your CAS without issue. I would definitely go that route rather than a virgin DME.

I think the 30A heater fuse is common for the 2 O2s. If it were the fuse, wouldn't the code be for both o2s?

 

[E90fanatic335]

Since the ISN has been hacked on the MSD80 and MSD81, a used ECU can be matched to your CAS without issue. I would definitely go that route rather than a virgin DME.

I think the 30A heater fuse is common for the 2 O2s. If it were the fuse, wouldn't the code be for both o2s?

My only fear is that a used DME may have problems itself. Does anyone know what part of the DME controls the o2 sensors? I've already tested the mosfets.

 

[E90fanatic335]

The fuse tested OK. And I ran the new wires from the DME to the sensor. The only wire not changed is the power since it's a common wire from a junction box that I didn't want to take apart. So far no codes but I only drove to work so fingers crossed. I'll report back.

 

[langsbr]

Did you purchase new pins to go into the DME connector and sensor plug or did you cut and splice? I have a bank 2 sensor that gets stuck quite a bit and was going to try running it dedicated, but I didn't want to cut the harness up.

 

[E90fanatic335]

Yes I used new pins for the wires. I won't ever splice into the wiring harness for fear of needed to replace it. I ran new wires along side the stock ones so that I can always go back to stock if need be. That's always my BMW rule of thumb, never mod something that can't be undone.

 

[langsbr]

Got a link to where to purchase them?

 

[E90fanatic335]

Got a link to where to purchase them?

My friend brought them home from the dealership. Best bet is to go to parts at your local dealership and tell them which pins for which connector that you need.

 

[langsbr]

My friend brought them home from the dealership. Best bet is to go to parts at your local dealership and tell them which pins for which connector that you need.

Gotcha, I think they list them as bushings strangely enough. Did he have the harness side of the o2 sensor plug as well, or did you repin the plug and just wrap the stock wires?