Fault moves with O2 sensor swap, but replacement doesn't solve (M54, E368, Z3 Coupe)

[jslbmw]

Hi, please help with something that has baffled me. I got post-cat O2 sensor codes, swapped the sensors side to side and saw the fault move. BUT, replacing the sensor did not did the problem.

Are there other meaning for codes that indicate something other than the sensor itself being a problem?
P0160 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)
P0161 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)
or
P0140 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
P0141 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2

History:

I got these codes indicating a faulty post-cat O2 sensor
P0160 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)
P0161 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)
----
I swapped post-cat/Sensor 2 between banks (Bank 1 to Bank 2, Bank 2 to Bank1) to see that fault moved, which it did.
----
Initially one fault occurred on bank 1.
P0141 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
So I replaced Bank 1 Sensor 2 O2 sensor with new and cleared code P0141 (1st time)
P0141 occurred again as well as + intermittent P0140(P) 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
Assuming that the new O2 sensor was faulty, I again replaced Bank 1 Sensor 2 O2 sensor with new and cleared code P0141 (2nd time)
Both faults then occurred
P0140 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
P0141 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
----
Just on the off chance that the pre-cat sensor was malfunctioning without codes, I replaced pre-cat/Sensor 1 Bank 2, cleared codes and P0140 and p0141 reoccurred
----
I then swapped back post-cat/Sensor 2 (Bank 1 to Bank 2, Bank 2 to Bank1) to see if the fault moved, which it did again, back to the original codes.
----
P0160 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)
P0161 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)
--------------------------------------------------


I'm at a loss. The codes indicate a sensor problem, confirmed by swapping sensors from one back to the other and having the fault move; and then after replacing the sensor twice, re-swapping and seeing the fault move again. Diagnostic computer also picks up no sensor problem.


If the fault moves with swapping, and replacing the sensor doesn't solve the problem, what can the problem be?

I guess it's possible that two new O2 sensors came faulty from the store, but it does seem unlikely.

Your help appreciated.

Jack
2001 Z3 Coupe M54, E368

[jslbmw]

Still no resolution.

[328 Power 04]

Did you have these faults the whole time while the car was in your possession, or did you buy it like this?

I'm just having a hard time following what exactly is going on.
It would also help to have true BMW oriented diagnostics, including logging, instead of generic P code reading.

[bmwdirtracer]

Hello, Jack,

Sorry I missed your earlier post, and welcome to the forum.

I would advise having your DME flashed with the most recent updates available. Yes, these will still be ten years old, but that's better than the 17 year old software that you're probably using. It's very possible that BMW had overly sensitive criteria for this parameter, and later corrected that criteria with updates.

You can have this done at any dealership, or any VERY well equipped independent BMW specialist shop which has ISTA-P. (I could do this, if I had the car itself, at my indie shop, but I cannot do it with just your DME....I have to have the car.)

Or, if you can do without your DME for a week, send a PM to 328 Power 04 (Abel), and ask him if you can send it to him for updating. He has performed many computer miracles for me and the shop I work for. A software update will not be a problem for him. You need to ask him what amount of money he'd like sent for his expertise and postage.

You can absolutely trust him, 100%.

Now, this MIGHT NOT fix your issue, but I would personally start here, given the history of your attempted (correct) fixes.

I'll PM Abel and ask him to have a look at your thread.

- - - Updated - - -

Look at that....He beat me to it. Thanks for being here Abel!

[jslbmw]

No, the codes haven't been there forever.

I've been too busy with other codes that appear to now have been resolved at last, so haven't done anything on the oxygen sensor. My focus is on that again. I'm going to go to a workshop and get the codes read. I've got old BMW diagnostic software which shows everything OK as it runs through its testing routine. Very strange.

- - - Updated - - -

Thanks Chris and Abel.. just thinking, that maybe just one more time I'll try a new sensor before going to a workshop. Maybe, just maybe, I got two duds in a row...

[MIKYZZ4]

I don't know what supplier you are obtaining your parts from,
but I strongly suggest that you use only BMW OE replacement parts,
or at the very least OEM replacements, which I believe are Bosch.
Substituting cheap, generic, aftermarket parts are well known to cause-
electrical gremlins or electronic anomalies with BMW systems.

[jslbmw]

The one that went faulty was a Bosch, as are the ones that I used to replace it with.

The car ran on the set of sensors for about 50K before the fault first appeared.

[328 Power 04]

Hmm, the reason why I ask if the car was always like that is if the software in the ecu has been modified by someone, or if the ecu itself has a fault. This is a strange situation. I can send you a replacement programmed DME with EWS disabled if it comes to that.

Maybe it's worthwhile to dig into the wiring and power supply to the sensors, as there is a common supply to both sensors at one point. A short may do weird things.

[shadowpuck]

i was just thinking the same thing on the wiring - it would seem there's something common to the circuit that is causing this issue. usually circuit errors point to wiring, driver issue on DME, etc....

[jslbmw]

I initially thought wiring/power issues might be the problem, but I discounted them when the fault moved from one bank to the other when I swapped the sensors.

This weekend I will buy another sensor and replace the indicated faulty one. If that solves the problem, it would mean that I did in fact buy two faulty ones out of the box in a row. I'll cheer if that is the case, even though it might be too late to claim refunds for the prior two.

If that doesn't solve the issue, a trip to my local mechanic (https://www.bimmershops.com/new-mexi...ge-santa-fe-nm) is in order. I know he has the latest BMW diagnostic equipment so assume he'll have the necessary equipment for the live logging suggested, and then possibly the DME fix you suggest, Abel.

Step by step, but I'm now dedicated to this particular problem until resolved.... before of course getting onto other outstanding ones.

Thank you all for your insight.

[MIKYZZ4]

Check the fuses in this fuse pack, I'm pretty sure one of them protects the o2 heater circuit:
http://www.bimmerfest.com/forums/att...3&d=1323057473
http://www.bimmerfest.com/forums/att...2&d=1323057473
I suspect the heater circuit is the cause of your problem, not the actual new o2 sensors.

[jslbmw]

Thanks for the suggestion; that was one of the first things I did... even though looked good, I replaced anyway.

[MIKYZZ4]

Hopefully live data will provide a clue to this mystery.

[jslbmw]

SOLVED - at least that's the indication after driving 60 miles without codes. I can hardly believe what it turned out to be, and I didn't even know the particular setup was possible, though at the end it was the only logical cause.

The fact that the fault moves when I swap sensors between banks, means it must be a faulty sensor, but replacing it doesn't fix it. After my last swap, the fault was on Bank 2 sensor 2. I got a new sensor last weekend, and again, replacing it made no difference. Because of the seeming illogic of the situation, I decided to disconnect bank 1 sensor 2 and go for a ride. What a shock - it came up with a new fault (P1155) on bank 2, not bank 1! I immediately lifted the car thinking that somehow, I must have mixed up the two banks, but no, I didn't. Yesterday I replaced the sensor on "bank 2", i.e. what should be bank 1, took it for ride and got no faults.

I woke up this morning convinced that I'd mistaken which bank is which, so to make absolutely sure that I hadn’t identified the banks incorrectly, I lifted the car again to check. No doubt about it, I had it right all along, which can only mean that bank 1 is cylinders 3-6, and bank 2, 1-3. I didn't know that this was strictly possible, but I know when it must have happened. About 55,000 miles ago, the original headers and exhaust system were replaced by after-market units (stainless headers, stainless high flow metal core catalytic converters, Spintech resonator, and dual stainless Magnaflow mufflers). I didn't do the work so don't know why it was done, but the leads to which the sensors connect, must have been swapped at the DME/ECS, or wherever it is that they terminate. Crazy, but that looks like a wrap.

[328 Power 04]

Bank 2 is definitely 4, 5, 6 though.
Unless the particular type of code reader isn't defined properly for BMW. This is why I only really trust BMW error codes.
P codes on BMW are a joke, nowhere near enough info for a proper repair. I think BMW made their cars barely compliant to OBD type codes.

[jslbmw]

It wasn't just my code reader. I recently had the fault memory list printed at a shop with the latest BMW diagnostics.
"000099 DME: Oxygen sensor voltage after catalytic converter, bank 2" &
"0000BF DME: Insufficient heat output, oxygen sensor behind catalytic converter, bank 2"
which correspond with the two I got from my reader:
P0160 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)
P0161 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)

It's pretty clear that the fault was on what a computer identified as bank 2, so I'm convinced that the conflicting data and resolution indicate my bank 2 is now 1, 2, 3, and has been since about 50K ago.

[bmwdirtracer]

Hello Jack,

Sorry I missed the crucial clue earlier. There was so much sensor swapping, and code details in the first post, that I missed the fact that the live data had never been viewed from each sensor, and then one sensor disconnected to see the correct bank disappeared.

On many newer BMWs, there's actually a code which says "O2 sensors swapped" I have encountered this issue on many BMWs over the years. When I see 1 bank lean and the other rich, or similar issues, you check this by unplugging one sensor and seeing which bank's data goes missing. Again, my apologies for not seeing this before you went through more hassles.


You need to reconsider your assumption about banks 1 and 2, though..

While the sensor plugs have obviously been swapped, the rest of the engine's sensors have NOT been swapped. The fuel injectors, for instance, are still being controlled by the DME as "Bank 1 = 1,2,3, Bank 2 = 4,5,6 Similarly, Secondary air will be read the same way, and knock sensors, et al.

Best solution is to just swap the plugs for the incorrectly reading O2 sensors.

If you don't correct this in this way, you will be having other codes and issues, because the DME will be receiving incorrect data for each group of 3 cylinders.

[jslbmw]

Hi Chris, no apologies are required or expected. My knowledge level is low, so going through hassles is part of the learning curve.

Your suggestion is enlightening, as I never would have thought of that. I recall from years ago being told by an acquaintance in a local BMW club that he had, after disconnecting all sensors, made the mistake of swapping the two pre-cat ones when reconnecting, and the car had complained violently. I assumed that the same would happen if the post-cat ones were swapped, but you're saying that that would not be the case. If so, it's certainly a more feasible, and likely explanation than my thought that the leads going back to the DME/ECS were swapped. If I understand correctly, my post-cat sensors are each reporting back data for the wrong bank, so that the computer is making adjustments to one bank when it should be making them to the other. All logical now.

I shall give it a go this weekend, Thank you. I assume fixing this would improve my fuel consumption.

[MIKYZZ4]

The sensor leads were mistakenly swapped and connected incorrectly when you had exhaust work done, quite common.
Swap them back to the correct configuration, issue solved.

[LPCapital]

Too bad you solved it Jack: now you won't have an excuse to call me every so once in a while!!!!!

[jslbmw]

Wanna bet? Hopefully see you in September......

[LPCapital]

Wanna bet? Hopefully see you in September......

You should drive out so I get a chance to sabotage something else... Hihihi!!!

[jslbmw]

If I am coming right there and back, I think I will do that. But right now a stopover in the Bay Area is on the cards.

[bmwdirtracer]

Fixing it is unlikely to have effect on your fuel consumption, and NOT fixing it won't cause any "violent" running issues. In a car of this generation, only the PRIMARY O2 sensors control fuel; the secondary sensors are really there to check the catalysts' efficiency. (If the primary sensor plugs got swapped, that would cause very significant problems.)

While you might get catalyst efficiency codes, the real importance is that you're aware that the banks themselves have not swapped in other parameters.

I'm very glad you've got the issue fixed!

Chris

[jslbmw]

I made the swap and all looks good, though there was a scare on the way. After about 15 miles, I got code P0420, Catalyst System Efficiency Below Threshold (Bank 1). Hoping that it was just a temporary imbalance due to the swap, I reset and have driven 45 miles since then, with no recurrence.

Thanks all for you thoughts, and especially to you Chris Powell, without whom I would have continued on, thinking that the problem was solved but oblivious to the fact that my post-cart sensors were swapped.