Fixing the KDDI iPhone 5 2G network "Maru Mondai"

It was brought to my attention yesterday by Andrew Wright that some KDDI iPhone 5 users are getting stuck with a 2G CDMA data connection.

The bad news is that so far, I've only noticed LTE reception in two locations, one of which is my home (which has WiFi anyway). Half of my commute, from Kasumigaseki to Yotsuya on the Marunouchi line, gives me GPRS signal. It's impossible to do anything with it. The Marunouchi line may be a subway line but even standing overground at both Kasumigaseki station and at Yotsuya station gives me weak GPRS signal.

According to the manual, the Maru symbol ○ is used to denote a 2G connection. In the case of KDDI, this is actually indicating a 1xRTT CDMA connection, which to the end user is the same as being stuck on GPRS in the US or Europe (Japan never used GSM voice or GPRS 2G data networks). Therefore a similar problem would not happen with Softbank, since if no 3G or LTE are available, there is nothing to fall back to – you'd just have no signal at all.

Update PRL

The fix quickly came out in the ensuing discussion. Dial *5050 and waiting for a recorded message that will update the PRL (Preferred Roaming List) to a higher version. It also took several tries for it to work. It would seem that Andrew's set up at the shop was probably incomplete, which will surprise no regular readers. See here for a growing list of the dumbest things we've been told at Japanese mobile shops.

I'm not sure if this is at all related to KDDI's "smart" LTE, where the network signals the phone upon entering an compatible LTE service area. The LTE radio on the KDDI iPhone is supposed to stay off in areas with no LTE coverage, saving power rather than searching in vain for a nonexistent network.

According to KDDI (J), the problem is believed to be related to switching between the 3G CDMA-2000 and LTE networks.

Procedure

(NOTE: this is sourced from Japanese so the actual English used on the iPhone could be slightly different)

Confirm PRL version: From the home screen, got to Settings → General → About/Information → Carrier.

Update PRL version if below v. 5

1. From within Japan dial *5050
2. Upon connection:
   • Listen to a recorded message (in Japanese) telling you to hang up and wait about 10 minutes while the list is updated, and that depending on your area, the update may be unsucessfual.
   • After 10 minutes, check the PRL version again and try to update (or change locations) if not on v. 5 (or higher).
3. Click "finish" (終了) after seeing a message saying that the R-UIM card data has been updated (au ICカードのデータ更新が完了しました).
4. Reboot the phone.