intermittent electronic fault

[mart_dev]

Hi all. With regards to the 4x4, ABS, DSC fault; My vehicle will sometimes display this error while at other times it won’t. I find that it is more common after a longer (one or two days) of not having used the vehicle, and will then not do it again for a week or more. Upon checking the fault code which is always the same old transmission ECU, the fault description reads “SUPPLY VOLTAGE”. It’s worth noting that I have had the battery tested and although the battery centre did say it needs charging, they were happy with the condition thereof. Yes, I also thought (sometimes still do think) it may be battery but that doesn’t explain the sporadic nature of the fault…or does it? Also, since this fault first presented itself I have a permanent fault with the VAC module. It has a continual fault which reads “THIRD ROW SEATING AIR TEMPERATURE SENSOR” or something very close to it. Up until the sporadic 4x4, ABS, DSC fault this fault was not active. Coincidence or linked?
Please chip in if you feel you may have even a guess as to what it may be but if it helps your diagnosis: The cruise control functions, as does the hill descent control. The ABS functions (yes I’ve tested) and the digital speedo also works so I imaging the wheel speed sensors are okay. I have even floored it on my lawn to test the traction control…it works

[ART-qitec]

When you get the 4X4, ABS, etc. error does you car go into limp mode and/or gas pedal becomes completely unresponsive?

[mart_dev]

No. Quite the opposite if I'm honest. Without drive to all four wheels it actually becomes a little more fun to drive although it's obviously devoid of any electronic assistance should things get out of hand. The absence of ABS is my only real concern since it is my wife's primary form of transport.

[ART-qitec]

Originally Posted by mart_dev

No. Quite the opposite if I'm honest. Without drive to all four wheels it actually becomes a little more fun to drive although it's obviously devoid of any electronic assistance should things get out of hand. The absence of ABS is my only real concern since it is my wife's primary form of transport.

Hmm, my best guess would be maybe the ABS speed sensor is going out intermittently and setting off the errors? Sorry I can't offer more info, I've never seen this issue before.

[ard]

Battery IMO

These arent the old days of dead or alive. Special algorithms for managing battery charging can lead to odd low voltage errors as batteries begin to fail-

If the battery is over 5 years old, getting a replacement is probably easier than spending $$ on more diagnostics.

my 2 cents

[mart_dev]

Thanks for the feedback. The battery is older than 3 years, that I know for sure but obviously I can't say if it was ever swapped out prior to me taking ownership.

[ard]

Originally Posted by mart_dev

Thanks for the feedback. The battery is older than 3 years, that I know for sure but obviously I can't say if it was ever swapped out prior to me taking ownership.

when you look at the battery is there a date on it???

Is it an OE battery?

[mart_dev]

Hi. It is an OEM unit. It's not an AGM battery however. The battery casing is white which I'm told is the conventional 90Ah wet cell and it is BMW branded although it isn't date stamped...for all I know it's the original but that might be a little optimistic since it's a 2008 model.

[ard]

You've owned it 3 years?

What makes you thing the prior owner would have replaced the OE battery in 2009, 2010 and 2011?

To me, if I had these issues Id be HAPPY to discover I had a 7 year old battery that might be the culprit. $100 -200 and you are good to go.

[mart_dev]

Hey Ard,
Yeah I hear you, and I can't argue with the logic. I just wanted to get as much info from as many guys as would be willing to offer any before buying a new battery (and paying for battery registration since I can't do that myself)...$300 is still real money. Thanks for the interest shown and I'll be sure to update this thread once the fault has been corrected.