Help me understand these fault codes and their causes (09 E82 128i)

[02Pilot]

SES popped on solid on my drive home. Joy. Pulled the codes: got two active, plus several more stored. The active are:

A0B5 CAS: Fault road speed signal
2C2D DME: Oxygen sensor before catalytic converter: coasting mode check

The stored codes are:

2DEB DME: Power management vehicle electrical system
2C3D DME: Oxygen sensor before catalytic converter: line fault
+ 2 ABS codes for the front left and right wheel speed sensors

I have had no previous SES lights in recent memory. I did have the ABS light come on a few times for wheel speed sensors, but all four have been replaced within the last year or two; the ABS light is not on now.

The oxygen sensor codes seem to suggest the sensor is on its way out - not surprising at 137k miles - but I don't know much about the exact faults, so clarification would help. I'm at a loss as to what's causing the CAS fault and the 2DEB power management fault. On the subject of the latter, however, I looked quickly at the live data and saw the battery voltage was 15v, which seems very high to me, but I know these cars have a fairly complex charging system, so any clarification of what the proper operating voltage should be would be helpful. Finally, is there anything in the live data or active test regime that I could use to pin down what's going on?

Oh, and really finally, I'm still chasing down an increasingly severe vibration from what seems likely to be the driveline - any chance any of these could be influenced by vibrations through the chassis? Seems unlikely to me, but I figured I'd mention it.

[dworthy]

Hello Amigo! So I am going to assume that you have erased the codes and these are the ones that keep coming back.

So for the A0B5 from my understanding is a wheel speed sensor isn't picking up properly. Or it might be that you have 1 tire worn more than the others. Also see if you can watch live data for each wheel to ensure they are reading properly.

The 2C2D would point towards aging sensor, as BMW recommends a change interval of 120k miles on the N-52 motor last I checked as they are wide band sensors.

For the 2DEB, I would double check the positive bus bar on the battery, and how old is the battery? Only time I would see it charging that high is when the battery is near the end of life, or somebody forgot to "reset" the registration in the DME. Remember that the alternator on that car doesn't have a voltage regulator, it's in the DME. As a side note, 15V on that car isn't too high, I would be worried if it went over 15.5v.

What speeds does the vibration show up at? You could be looking at a bad half-shaft here.

[02Pilot]

Thanks for the insights. The light just illuminated yesterday afternoon, so I have not erased the codes yet, mostly because I wanted to decide if it was worth the trouble of bothering the dealership about the SULEV warranty (in which case they'll need the o2 sensor codes present), or if I should just replace the sensors myself.

The wheel speed sensors are all relatively new OE parts, due to previous recent failures. The odd thing about this is that the SES is on and the ABS is off; previously, the opposite was true (ABS on, SES off). Tires are evenly worn and only a couple years old.

The battery was replaced five years ago by the PO. Dealership supplied and installed the battery, so I'm assuming it was coded properly. Good to know about the voltage - I'll check it at the battery and see if it matches the scanner.

The vibration is an ongoing problem. It started as a low drone and slight chassis vibration. I couldn't pin it down, nor could my indy. Neither of us saw anything that was in imminent danger of failing, so we decided I would keep driving and see what happened. It's gotten progressively worse. From 40mph up and in gear, it's there in every throttle position except for just barely cracked open (basically holding RPM). The further away you get from that neutral throttle position, the louder it gets, especially when opening the throttle. I've also noticed that it spikes just as the clutch is being engaged (pedal released), as if the transfer of torque from the clutch being engaged is applying greater transient pressure on whatever's cause the problem before it levels out to a more constant state. I've definitively ruled out tires, as it remains the same with the snows mounted.

It doesn't sound like any gear noise I've ever heard, so I'm thinking it's either a bearing or the exhaust. Bearing seems more likely to me, as if it were the exhaust, why wouldn't it do it at lower speeds? It can be provoked at lower speeds by hard throttle, but normally it's not evident below 40mph. There's no sign of it revving in neutral. If it is a bearing, I can only think of a few possible culprits: transmission output bearing, center support bearing, and diff input and output bearings. Right now I'm thinking the center support bearing is the top of the list, as the rubber mount would allow it to react to torque changes more than the others. I've never had a center support bearing fail; usually the rubber mounting fails, but the bearing is still good, resulting in the driveshaft banging around. That's not what's happening here.

[jclausen]

If the battery is five years old I would replace it, because of the power management fault

[dworthy]

BLUF, check your rims.

So having thought about the odd vibration you get, on the wagon if found out that I have 2 warped rims on the winter set, one was more warped than the second. Had 1 up front, and 1 on the rear, when I rotated the tires, the vibration lessened a bit. What clued me in was the bearing noise sounds, for it didn't do that on the summer tires I just took off a month or so ago. I had cleaned all the hubs, as well as both sides of the rotors, this reduced the sound some, but not all the way. How I found the warped rims, was by lying them on a flat surface and they wobbled just a little bit.

[02Pilot]

I'm 99.9% sure it's not the wheels. Nothing changed when I went from the summer set to the winter set.

[02Pilot]

Update on the vibration issue: Took it to my indy and we put it on the lift and ran it. The vibration is still present, but not as strong without the interaction with the road. He seems inclined to think it may be internal to the transmission, or possibly the clutch or flywheel, though he didn't hear anything definitive with a stethoscope. Nothing is visibly shaking, nor are there any signs of anything rubbing. I fear this means I'm going to have to start throwing parts at it, or wait for it to blow up.

[dworthy]

Or see if you find somebody who will let you run it on a Dyno to see if you can find the vibration that way.