Ever since I got my 2006 IS250, there's been one thing that constantly annoyed me: not being able to enable automatic locking and unlocking of the doors.
From what I've gathered, it seems that American models had it from the beginning, but European models only received it with the 2007/08 update.

Armed with this knowledge, I set out to find out what part actually needs to be upgraded. After looking in the repair manual, it turned out to be the Main Body ECU RH, located in the Cowl Side J/B RH, behind the glove box.
However, taking a look at a parts catalog reveals that there's no separate part number for the Body ECU and you can only get it together with the Junction Box assembly. In addition to this, there are tens of variations of the junction box assy, according to the destination market and the various option packages. Finding information about these modules is really hard, as the part number from the catalog isn't printed on the part itself.

Anyway, I figured it's worth a try to find a 2008+ Junction Box assembly and only swap the ECU.

A couple of days later, this arrived:

This one came out of a 2010 LHD IS220d. Honestly, I had low hopes of this working, as it came from a car with a different engine and option package.
To access the junction box, you need to remove the glove box and the knee airbag.


Getting to the ECU is easy. You need to unclip the cover which also houses the gateway ECU.


You only need to remove the 3 silver screws and pry from under it. Care must be taken not to break the connector that's on the bottom part of the board. Using a screwdriver around the 2 circled spots works best:

After finally getting it free, we can compare it to the old one. Left - new, right - old:
The part numbers are:
89221-53140 - 2006 IS250
89221-53161 - 2010 IS220d (presumably same part number for all engines and configurations)

Since the boards look identical, I believe they only changed the microcontroller firmware and EEPROM. The EEPROM probably stores the region information, and the microcontroller decides which functions to enable based on that.

While I was here, I also decided to swap the Gateway ECU, since I already had it on hand. Here they are, side by side. Left - new, right - old:

This might open the door for more upgrades and retrofits in the future (e.g. automatic folding mirrors).

Like I said, I had low hopes of this working. Because the donor car had a different configuration, I expected all sorts of weird issues: alarm sounding, power windows going crazy, headlights not working and the dash lighting up like a Christmas tree.
After turning on the ignition, I was surprised to find that none of that happened. Everything seemed to be normal, so I went ahead and tried the procedure for auto locking doors described in the US owners manual:


Disappointingly, this did nothing. However, not all hope was lost: I fired up Techstream and entered Customize Functions for the Body Control Module. Lo and behold, two new options appeared: Auto Lock and All Unlock/Open-Close:


After setting them to on, I went for a drive and everything seems to work perfectly! The doors now lock automatically when going over 20 km/h and all the doors unlock after opening the driver's door.

Hopefully this helps someone in the future, as information about the Body Control Module is very hard to find on the internet.

 

Nice work there. Thanks for sharing it with all of us.