# uConsole 4G (SIM7600): why you have to restart ModemManager after enabling the modem, and a patch that fixes it

**URL:** <https://forum.clockworkpi.com/t/uconsole-4g-sim7600-why-you-have-to-restart-modemmanager-after-enabling-the-modem-and-a-patch-that-fixes-it/23816>\
**Category:** uConsole\
**Tags:** lte, cm4, 4g, modemmanager\
**Created:** [November 11, 2026, 8:25am UTC](https://forum.clockworkpi.com/t/uconsole-4g-sim7600-why-you-have-to-restart-modemmanager-after-enabling-the-modem-and-a-patch-that-fixes-it/23816 "2026-11-11T08:25:27Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![jose1711](https://yyz1.discourse-cdn.com/flex029/user_avatar/forum.clockworkpi.com/jose1711/32/16021_2.png) [@jose1711](https://forum.clockworkpi.com/u/jose1711)\
**Post date:** [November 11, 2026, 8:25am UTC](https://forum.clockworkpi.com/t/uconsole-4g-sim7600-why-you-have-to-restart-modemmanager-after-enabling-the-modem-and-a-patch-that-fixes-it/23816/1 "2026-11-11T08:25:27Z")

</div>

If you use the 4G module and your routine is `uconsole-4g-cm4 enable`, then `sleep`, then `sudo systemctl restart ModemManager`, or if NetworkManager sometimes refuses to connect with

```auto
Connection requested IPv4 but IPv4 is unsupported by the modem

```

or

```auto
Connection requested both IPv4 and IPv6 but dual-stack addressing is unsupported by the modem

```

this post explains the cause and gives a fix.

**Setup:** uConsole CM4, SIM7600G-H in 9001 mode (USB `1e0e:9001`, PPP on `ttyUSB2`), Debian 13 (Trixie), ModemManager 1.24.0, NetworkManager 1.52.1.

### Cause

After power-on, the modem appears on USB well before it has finished initializing its SIM. ModemManager probes it about 10 s later. During initialization ModemManager asks the modem which PDP types it supports (`AT+CGDCONT=?`), and if the modem isn’t ready yet, it answers `ERROR`:

```auto
[ttyUSB2/at] --> 'AT+CGDCONT=?'
[ttyUSB2/at] <-- 'ERROR'
[ttyUSB2/at] <-- '+CPIN: READY' (half a second later)
[ttyUSB2/at] <-- 'SMS DONE'
[ttyUSB2/at] <-- 'PB DONE'

```

ModemManager logs that error only at debug level and never repeats the query. The modem then looks fine (enabled, registered, attached), but its “supported IP families” stay empty. NetworkManager therefore rejects every connection attempt until ModemManager is restarted, which is why the restart trick works. Whether you hit it depends on how fast the modem boots, so it can come and go “by itself”.

Check whether this is your problem:

```auto
mmcli -m any --output-keyvalue | grep supported-ip-families

```

`--` means you are affected. A working modem shows `ipv4` / `ipv6` / `ipv4v6`.

### Fix

A small ModemManager patch makes it retry the query every 2 s for up to 30 s. I tested it with an automated A/B test, 20 modem power-cycles per build, on the same device and SIM:

| Build | Modem initialized | Connected |
| --- | --- | --- |
| stock ModemManager 1.24.0 | 4/20 | 4/20 |
| patched | 20/20 | 19/20\* |

\* The one failure was caused by the test script itself, not by ModemManager.

With the patched build, `uconsole-4g-cm4 enable` is enough and NetworkManager connects on its own. No ModemManager restart, no `sleep`.

The patch, a Debian rebuild recipe, the test script and an improved enable script (it still restarts ModemManager in the rarer `sim-missing` / `unknown-capabilities` cases the patch does not cover) are here:

> **[GitHub - jose1711/uconsole-tweaks: uConsole tweaks: display-auto, LTE/ModemManager...](https://github.com/jose1711/uconsole-tweaks)**
>
> uConsole tweaks: display-auto, LTE/ModemManager fixes, power key patch

Notes:

- You have to rebuild the `modemmanager` package yourself and put it on hold (`apt-mark hold`), so security updates for it then need re-patching by hand.
- If you use IPv4 only, also set `ipv6.method disabled` on the NetworkManager GSM connection.
- I plan to report this upstream to ModemManager, so that a proper fix ends up in the package.

### Other things that can make the modem fail

These are not fixed by the patch:

- **Low battery.** The modem’s current peaks while transmitting can reset the internal USB hub. The modem _and the keyboard_ drop off USB (`usb usb1-port1: disabled by hub (EMI?)`), sometimes until a reboot. Use a charger or a well-charged battery.
- **Weak signal / small antenna.** This means higher transmit power, `Network timeout` errors and modem resets.

### Disclosure

I gave these problems to Claude (Anthropic’s AI assistant, in Claude Code) as tasks. The analysis, the patches and the scripts were written by Claude. I tested them on my uConsole. Tested on one device only, so read before you apply anything as root.

### Related threads

- Same dual-stack error: [4g problem with Trixie 6.12 and Telekom](https://forum.clockworkpi.com/t/4g-problem-with-trixie-6-12-and-telekom/22234)
- Restart workaround: [uConsole LTE Modem How-To Guide (for A06 with 9001 stock firmware)](https://forum.clockworkpi.com/t/uconsole-lte-modem-how-to-guide-for-a06-with-9001-stock-firmware/11347) , [Uconsole 4G module connection issue - #18 by DeRock25](https://forum.clockworkpi.com/t/uconsole-4g-module-connection-issue/13533/18) , [Cellular Modem Service - #17 by DeRock25](https://forum.clockworkpi.com/t/cellular-modem-service/12217/17)

---

<div class="post-metadata">

**Author:** ![michaelwilson](https://avatars.discourse-cdn.com/v4/letter/m/6bbea6/32.png) [@michaelwilson](https://forum.clockworkpi.com/u/michaelwilson)\
**Post date:** [November 11, 2026, 11:18am UTC](https://forum.clockworkpi.com/t/uconsole-4g-sim7600-why-you-have-to-restart-modemmanager-after-enabling-the-modem-and-a-patch-that-fixes-it/23816/2 "2026-11-11T11:18:18Z")

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The timing explanation makes sense: the PDP-type query going out before the SIM is ready would leave supported-ip-families unset, and that matches the NetworkManager errors you quoted. The mmcli check is a useful way to confirm it, since an empty value is easy to spot. One thing I’d want to know is whether the retry patch ever delays normal modem detection on units that initialize quickly, and whether you’ve seen it hold up across reboots rather than just power-cycles. Your A/B numbers should make that clear.

---

<div class="post-metadata">

**Author:** ![jose1711](https://yyz1.discourse-cdn.com/flex029/user_avatar/forum.clockworkpi.com/jose1711/32/16021_2.png) [@jose1711](https://forum.clockworkpi.com/u/jose1711)\
**Post date:** [November 11, 2026, 12:12pm UTC](https://forum.clockworkpi.com/t/uconsole-4g-sim7600-why-you-have-to-restart-modemmanager-after-enabling-the-modem-and-a-patch-that-fixes-it/23816/3 "2026-11-11T12:12:52Z")

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Thanks. On both points:

**Fast-initializing modems:** the retry only kicks in when `AT+CGDCONT=?` returns an error. If the modem answers the first time, the code path is the same as stock and nothing is delayed. In the A/B test the time from power-on to an initialized modem was 27–31 s for both builds. 11 of the 20 patched cycles needed one retry (2 s), and that didn’t change the total noticeably, because the rest of the init takes longer anyway.

**Reboots vs. power-cycles:** the automated test only power-cycled the modem (via GPIO, without rebooting the CM4). I also rebooted a few times with the patched build. After each reboot `uconsole-4g-cm4 enable` was enough and NM connected without needing a restart. After a reboot the modem starts powered off and `enable` turns it on, so MM sees the same sequence as in the test. That’s a handful of reboots, not 20, so more reports from other units are welcome.

**Upstream:** I’ve reported it to ModemManager now: [Making sure you're not a bot!](https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/work_items/1120)  
The problem itself isn’t new. The SIM7600 answering too early while it boots is already in [#725](https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/725). Empty supported IP families (“IPv4 is unsupported by the modem”) came up on modemmanager-devel in 2024 and in [#705](https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/705). Here on the forum, people have used the “restart ModemManager after enable” workaround for years. As far as I can tell, nobody had tracked it down to the one failed `AT+CGDCONT=?` query, and no fix has gone in so far.

---

<div class="post-metadata">

**Author:** ![DeRock25](https://yyz1.discourse-cdn.com/flex029/user_avatar/forum.clockworkpi.com/derock25/32/7976_2.png) [@DeRock25](https://forum.clockworkpi.com/u/DeRock25)\
**Post date:** [November 11, 2026, 2:45pm UTC](https://forum.clockworkpi.com/t/uconsole-4g-sim7600-why-you-have-to-restart-modemmanager-after-enabling-the-modem-and-a-patch-that-fixes-it/23816/4 "2026-11-11T14:45:11Z")

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I used the delay script, just because cpi had a tread about using the modem when the uconsole first released and talked about boot time. Also works well to use scripts because the AIO had a lora module boot time too… One of the things you deal with when using the ext port. Awesome for the community to contribute to the larger world though!