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      07-21-2015, 06:11 AM   #1
chillindrdude
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Rear axle differential lock?

got a "rear axle differential lock" fault message this weekend at the track.

it occurred between the 2nd and 3rd session of my second day. i was putting the car into neutral keep off the pads in the paddock.

track temps were pretty warm....95 degrees air temp, humidity>50%. Track surface temps were probably close to 130-140 degrees.

i pulled the car into an air conditioned garage, let it cool. re-powered it, hoping the message would clear, it didn't.

my day was done

leaving the car overnight, the next morning, the error was gone! but that was short lived. as around noontime, with the hot sun, the message came back when restarting the car after returning from lunch.

car was still driveable, i just had esssentially a solid axle car. i was able to drive home, with no discernable wierd noises or drivetrain jerkiness.

it seems related to temperature. the differential fluid was changed at break in service. this fault appears to be rare *sigh*

the rare victims had to have their GHAS Control unit replaced and some, their entire differential.
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      07-21-2015, 08:42 AM   #2
Gearhead999s
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I have had that warning in the hard memory of my car but I think that was very early in my cars life and I have never seen it since.
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      07-21-2015, 11:34 AM   #3
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Entire diff replaced is not a bad thing. Does seem like a rare fault. A lot of use have tracked in those ambient conditions.

Hope you get if fixed soon.
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      07-23-2015, 07:02 PM   #4
chillindrdude
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got my car back...

the master M tech at my local BMW dealership has never seen this fault before. So troubleshooting escalated up to BMW Corporate. the GHAS differential control module was directly interrogated. fault code present. confirmed to be heat related. M tech instructed to check electronic and mechanical connections for signs of heat damage. All visually appear to be undamaged and secure. the control module itself was reinitialized (rebooted). came back on-line as usual, output signals verified, fault codes cleared. Service manager took the car out for a test drive, I assumed he pounded on it pretty good (in mid-day 85 degree temperatures). No issues.

so that's it. i asked the service advisor if the fault could happen again in similar track conditions as before. he admitted it's certainly possible, but the service was performed as instructed by BMW corporate. I surmise, if it happens again then a control module replacement or worse, differential replacement would be the next course of action.
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