[mictang]

So I have been getting some O2 codes with no CEL for almost over a year now, checked and eliminated a few things along the way and I am now pretty sure it's the O2 sensor itself that's gone bad, can anyone confirm my theory?

I had the following codes pretty consistently:

2018/09/12
2C7E Lambda probe behind catalytic converter, trimming control
2C6A Lambda probe behind catalytic converter, muddled

2018/06/20
2C7E Lambda probe behind catalytic converter, trimming control
2C6A Lambda probe behind catalytic converter, muddled
2C7F Lambda probe behind catalytic converter 2, trimming control

2018/04/09
2C7E Lambda probe behind catalytic converter, trimming control
2C6A Lambda probe behind catalytic converter, muddled
2C2B Lambda probe in front of catalytic converter, system check
2C6C Lambda probe behind catalytic converter 2, system check
2D06 air mass system

2018/02/10
2C7E Lambda probe behind catalytic converter, trimming control
2C6A Lambda probe behind catalytic converter, muddled
2C2B Lambda probe in front of catalytic converter, system check
2C6C Lambda probe behind catalytic converter 2, system check

I am thinking they are caused by the bank 1 before cat sensor? Am I right? (I did check the after cat connectors and they cannot be mixed up as they are physically different)

When I first got the code I had some oil seeping from the valve stem guides and I have managed to contain it with Liqui Moly Oil Saver down to maybe ~7,000km/L oil used. (also interestingly after the first 7,000km, the Liqui Moly seems to wear off and car burns another liter in less than 3,000km)

So I don't think oil consumption is still causing the codes now (it could have already ruined the o2 sensors before I guess?)

Spark plugs looked pretty white (all six of them, but only code for bank 1?) compared to my other car and got whiter with time, no drive-ability issue though and MPG is just a hair under advertised values (~8.6L/100km or 28 US MPG @ 120kph/74mph highway cruising, MT 325i with N52B25).

My plan is just to replace the bank 1 sensor and see what happens, any comments/advice?

Screenshots from ISTA:

[IanARB]

mictang,

What was your result of replacing the bank 1 pre-cat sensor? Did you still experience problems and did you take any further steps to remediate the codes? Hope you were able to solve your issues.

I'm experiencing similar codes and am looking for the reason. My mechanic had said replacing the catalytic converters would be a $3000 job so if the O2 Sensors are to blame I'd like to experiment there first.

[dpaul]

Originally Posted by mictang

2018/09/12
2C7E Lambda probe behind catalytic converter, trimming control
2C6A Lambda probe behind catalytic converter, muddled

2018/06/20
2C7E Lambda probe behind catalytic converter, trimming control
2C6A Lambda probe behind catalytic converter, muddled
2C7F Lambda probe behind catalytic converter 2, trimming control

2018/04/09
2C7E Lambda probe behind catalytic converter, trimming control
2C6A Lambda probe behind catalytic converter, muddled
2C2B Lambda probe in front of catalytic converter, system check
2C6C Lambda probe behind catalytic converter 2, system check
2D06 air mass system

2018/02/10
2C7E Lambda probe behind catalytic converter, trimming control
2C6A Lambda probe behind catalytic converter, muddled
2C2B Lambda probe in front of catalytic converter, system check
2C6C Lambda probe behind catalytic converter 2, system check

I am thinking they are caused by the bank 1 before cat sensor? Am I right?

Why would you think that? The consistent thing about your codes is that BOTH BANKS report problems AFTER THE CATS. How is a problem with the bank 1 pre-cat sensor going to cause a code on bank 2 post-cat?

What mods do you have, what were the "things you did along the way", how many miles on the car and the sensors