6Hp26 harsh 2-1 downshift - possible solution (at least one of them)

[Doru]

My X was driving really good, and about 2 weeks ago it started this 2-1 hard downshift/upshift but only with stone cold engine & transmission.

I knew I had the correct ATF level. The tranny was serviced not too long ago with the correct ZF fluid etc.

There are numerous threads and on-line resources tackling this issue and the "possible" causes are from failed flex disc (guibo) to clogged solenoids, need of new mechatronic unit, low ATF level, etc.

There is also mention of low battery level. And in my case I think this is what it all started, but this is not everything.

You could perform the 2-1 tip in procedure (key in pos II, gas pedal depressed all the way for 30 sec) which is actually a way to reset adaption values if one doesn't have the software (INPA, GT1, etc), but it might only last for 1 or 2 weeks to only return.
In my case, I reset adaption values, but the hard 2-1 shift was still there for the first try, then it faded away. The X was again driving OK, but not quite right (not sure how to explain, to me it seemed the shifts were a bit off from what they usually were).

So, yesterday I decided to see if I have the latest software applied to the tranny, which apparently fixes the 2-1 hard shift issue.

When doing this procedure, you have to bear in mind that the facelift X5 with the 6Hp26 transmission is a bit different from the previous 5 speed tranny. It does not have the "regular" transmission module the famous EGS. So DO NOT SELECT THIS OPTION, you might brick the tranny.
The 6Hp26 has the module incorporated in the mechatronics unit and is called GKE. Select this one when upgrading/re-flashing the module.

Also pay attention to the 2 EGS programmed number & basic number (see below the SIB - they are different for the 4.4 & 4.8) - I know I said EGS, but this is how Progman will ask for it, even prior you have selected GKE. Once you go through the motions explained in the below SIB, you will notice that the computer might be "stuck" as in timed out. It might last 20 minutes or so. Just be patient.

In my case, after I did what is outlined in the below SIB, the X performed exceptionally well on the test drive.

So here is my conclusion: These modules are finicky, and we all know this, testament the "Trans-Failsafe Program" of the tranny when the battery is low, or numerous glitches related to low battery. The thing does not stop here, I believe. You can re-charge the battery, or install a brand new battery, or install a new alternator. What I think happened in my case is the low battery triggered the hard 2-1 shift which is probably at the brink of the "trans-failsafe" program. And I think, once this happens, the GKE module is compromised (Remember I reset the adaptation values, but at first it didn't catch, then shifting wasn't quite right). In my case the solution was to re-flash the GKE - and yes, I had the latest software confirmed by the program.

Also, if you attempt this, make sure you have a good charger (BMW recommends a 40Amp charger), but I got by with a 12 Amp charger, which I think is the bare minimum.

below is the SIB 24 01 06 (again, when using Progman select GKE and NOT EGS - you are warned):

Automatic Transmission

August 2007
Technical Service

This Service Information bulletin supersedes S.I. B24 01 06 dated November 2006.
[NEW] designates changes to this revision
SUBJECT
E53 X5 N62 - Harsh 2-1 Downshift

MODEL
X5 4.4i/4.8is with 6HP26 from 10/03 up to 08/05

SITUATION
Customer may complain of the following:

- An excessively harsh 2-1 downshift when decelerating to a stop, or
- Transmission "bangs" into gear when accelerating from a full stop, or from a "rolling stop" (vehicle did not come to a complete stop).
CAUSE
EGS software.

CORRECTION
On a customer complaint basis only, reprogram transmission control module (EGS/GKE) with SSS loaded with on-line update Progman V20.01.00, or higher.

After programming is successfully completed, the following EGS part numbers should be displayed in the module identification page:
[NEW] X5 4.4i
EGS programmed number 7 564 917,
EGS basic number 7 557 063.

[NEW] X5 4.8is
EGS programmed number 7 564 921,
EGS basic number 7 557 063

PROCEDURE
Important:
Prior to EGS module reprogramming, transmission temperature must remain below 50 deg C and transmission shifter be must be placed in a P position.

To reprogram the EGS transmission control module:
1. Connect the vehicle to a BMW approved battery charger.
2. Connect SSS loaded with CIP 20.01.00 (on-line update), or higher.
3. Select: X line of vehicles, and then E53.
4. Question: Were any control modules replaced? is displayed. Select: No.
5. From the right-hand column select: EGS, then Programming, then Update software.
6. After few minutes, the measure plan is going to be displayed. Select Accept, and then Start.
7. Follow screen instructions.
WARRANTY INFORMATION
Covered under the terms of the BMW New Vehicle Limited Warranty.