[orionredwing]

My car has almost 50K miles now, and I've been through a slew of HPFP, and injector replacements.

However, I was still getting misfiring despire all recent replacements, and finally troubleshot it to 2 bad front O2 sensors. Here are my BT scans:

So if you're still getting misfiring despite replacing injectors, etc take a look at your codes and see if it's related to the O2 sensors. The O2 sensors play a part in your air/fuel mixture (the air part obviously), and was causing my car to idle a little bit rough (leading to misfire), etc. The idle was just slightly rough, and I never even realized it was there until I had the O2 sensors replaced and it became silky smooth again.

I've had this problem for 4 months, and am glad to finally get it resolved. It was a peeling the onion process to fix and eliminate the codes 1 by 1.

Even though I was still under warranty, I had this particular problem fixed out of pocket due to my mods. Some of you may have been ballsy enough to hit the dealer with it, but I wasn't comfortable doing it; guess I'm just too honest Pay to play


2CAA:
2CAA Lambdaprobe before catalyst, temperature
Error will cause a warning light
Error is not currently present
Test conditions have been completed
Short circuit or signal interruption
Freeze Frame Information
Event 1Odometer 79752kms 49555miles
symptom Lambda probe heating in front of catalytic converter bank 1 1.00 0-n
Battery Voltage 14.08 V
Lambda probe heating in front of catalytic converter bank 1 69.92 %
voltage Lambda probe in front of catalytic converter bank 1 1.99 V
Event 2Odometer 79768kms 49565miles
symptom Lambda probe heating in front of catalytic converter bank 1 1.00 0-n
Battery Voltage 14.08 V
Lambda probe heating in front of catalytic converter bank 1 69.92 %
voltage Lambda probe in front of catalytic converter bank 1 1.97 V


2CA6:
2CA6 Lambda probe heating in front of catalytic converter, function
Error will cause a warning light
Error is not currently present
Test conditions have been completed
Short circuit or signal interruption
Freeze Frame Information
Event 1Odometer 79752kms 49555miles
symptom Lambda probe heating in front of catalytic converter bank 1 1.00 0-n
Battery Voltage 14.34 V
Lambda probe heating in front of catalytic converter bank 1 35.94 %
ceramic temperature Lambda probe in front of catalytic converter bank 1 0.00 °C
Event 2Odometer 79768kms 49565miles
symptom Lambda probe heating in front of catalytic converter bank 1 1.00 0-n
Battery Voltage 13.82 V
Lambda probe heating in front of catalytic converter bank 1 30.08 %
ceramic temperature Lambda probe in front of catalytic converter bank 1 0.00 °C

[zsapphire7]

the front ones right next to the turbos were the culprit ??

[Asclepius]

Had a similar problem with o2 sensors. Also paid outta pocket.....$711....that put a nice dent in my mod money lol!

[orionredwing]

They're the front ones right before the cats. Are those right next to the turbos? Both replaced, and my car's running like a charm now.

No more error codes on startup like you saw when we went for the test drive. Finally, some enjoyment out of the car

Heading to Laguna on Mon, so hoping for good weather.

Originally Posted by zsapphire7

the front ones right next to the turbos were the culprit ??

[scalbert]

Originally Posted by orionredwing

They're the front ones right before the cats. Are those right next to the turbos?

Yes, they are inches from the turbine outlet.

Glad to hear you got your issues resolved.

[boom]

I get a 2C7E code for the rear o2 sensor on bank one after putting in my catted dps. I was super careful but I guess they're just fragile. I've done dps on numerous cars and never had any issue or been as careful as I was before this time. Tischer ftw at $180.

[john boxter]

Originally Posted by Asclepius

Had a similar problem with o2 sensors. Also paid outta pocket.....$711....that put a nice dent in my mod money lol!

why did you pay 711? i hope thats for the downpipes and the o2 sims together

[orionredwing]

Good deal. My mechanic gave me a 20% discount off retail so it came out to $180 ea too.

As for the O2 sensors, yes it's deceiving! I was wondering if my mechanic messed up during the DP install, but he pulled the bad ones to show me, and ask me if I could spot anything wrong visually?

I couldn't. The part looked perfect, the harness wasn't damaged, no wires were pulled, and it wasn't installed improperly (no threads stripped). It just went bad.

From your own experience, I'm wondering if the sensors are so fragile, that the act of disconnecting and reconnecting them caused it to fail. It doesn't make sense, but it's weird how we both failed right after a DP install.

Originally Posted by boom

I get a 2C7E code for the rear o2 sensor on bank one after putting in my catted dps. I was super careful but I guess they're just fragile. I've done dps on numerous cars and never had any issue or been as careful as I was before this time. Tischer ftw at $180.

[Asclepius]

Originally Posted by john boxter

why did you pay 711? i hope thats for the downpipes and the o2 sims together

No $711 was parts n labour for o2 sensors not sims. Replaced them at the dealer. Thought i would be covered under warranty, buy they blamed my downpipes.

[persian54]

What is the sensor that's by the charge pipe?

If you don't have DPs... (I do but let's say if...), would the dealer replace the sensors for free?

[zsapphire7]

Originally Posted by boom

I get a 2C7E code for the rear o2 sensor on bank one after putting in my catted dps. I was super careful but I guess they're just fragile. I've done dps on numerous cars and never had any issue or been as careful as I was before this time. Tischer ftw at $180.

And did changing the rear o2 sensors work?

[orionredwing]

It looks like another thread popped up that looks like a bad O2 sensor:

http://www.e90post.com/forums/showth...65#post6616565

His is bank 2 whereas mine is bank 1.

My mechanic actually showed me how to test which bank it is, in case you want to save $180 instead of replacing both front sensors. I guess I could've done that, but at the time, we weren't sure it was the O2 sensors. Now that I confirmed it (my car is fixed), you guys can save some money and just order the sensor that went bad.

1) To test simply open up the hood.

2) Follow the PROcede video or JB instructons to remove the microfilter, etc. You can stop at the point where you open up the ECU box.

3) Instead, remove the engine cover. The previous steps was to allow easier access.

4) You will see 2 connectors on the top, on the right hand side. These are your pre-cat front O2 sensors (bank 1 and bank 2) connections. The sensor itself is actually further down, so sorry, it's not that easy to change out

5) Clear your codes and start your car.

6) Disconnect 1 connector. The SES light will come on. Read the code. It will tell you which bank it is.

7) Stop the car, clear codes, reconnect the sensor and repeat for the other, verifying it's the other bank.

8) Go and replace the sensor that your codes are throwing. This check only applies to the front O2 sensors. I didn't ask how to check the rear ones, and I didn't pay attention whether the connection always came up top. I have the Bentley service manual though, so if someone is having rear O2 sensor probs, I can probably look it up.

http://www.amazon.com/BMW-E90-E91-Se...4720879&sr=8-1

Good luck!

[boom]

Originally Posted by zsapphire7

And did changing the rear o2 sensors work?

It did not. The BT voltage for that sensor shows a consistent 0.04V while the bank 2 sensor voltage is ~0.67. Weirdly though it does move around when driving very similarly to bank 2 but just a about an order of magnitude less than bank 2. This is exactly the same behavior as the original sensor - which I now think was fine. I'm wondering if position of the sensor in relation to the cat has anything to do with it.

[cn555ic]

Damn those sensors are made expensive....Does it come with the entire wire harnass?

[Lotus77]

Question: Can an expired O2 sensor lead to misfires?

I have a few CEL codes, 2 are for Bank 1 (cyl 1-3) too lean, and stuck lean O2 sensor 1. The other codes are for cyl. 4-6 misfires. The car is slightly rough on idle and when cruising. Gas mileage is terrible. Accelerating seems fine.

I think it's bank1, sensor1 O2 sensor, my mechanic thinks it's bad coils. If it's the bad O2 sensor, how can that cause cyl. 4-6 to misfire?

[n54Xdinan]

Originally Posted by Lotus77

Question: Can an expired O2 sensor lead to misfires?

I have a few CEL codes, 2 are for Bank 1 (cyl 1-3) too lean, and stuck lean O2 sensor 1. The other codes are for cyl. 4-6 misfires. The car is slightly rough on idle and when cruising. Gas mileage is terrible. Accelerating seems fine.

I think it's bank1, sensor1 O2 sensor, my mechanic thinks it's bad coils. If it's the bad O2 sensor, how can that cause cyl. 4-6 to misfire?

Lotus77.. what was the cause of your issue? re: your cyl 1-3 misfire... Bad pre-cat o2 sensor(s)?? Or, was it a coil issue??

Bryan
08 335xi Coupe
04 525i
00 540i

[GEOS07335i]

This happened to me. I was troubleshooting SES, misfires, rough idle, black soot coming out the tail pipe, foul gas smell. After replacing all injectors, plugs, coils, cleaning PCV valve, cleaning Vanos solenoids, compression test, Walnut blast etc... nothing fixed my rough idle and black soot gas smell. Misfires indicated cyl 4 and 6 so this was BANK2. In a desperate attempt not to go to an INDY I swapped out both PRE CAT O2 sensors and that fixed my problem. BANK1 is cyl 1,2,3 BANK 2 cyl 4,5,6 if your getting multiple misfires on either bank that would indicate which O2 sensor to swap out first. I did not get a single error code indicating it was an O2 sensors that was the fun bit.

O2 sensors are only good for 100-120K miles and are considered a regular maintenance item. The gotcha is there kind of pricy. Start with the Pre-cat and go from there there.