iPhone 17 Pro Max iPhone 17 (Pro / Pro Max) – Cellular modem fails to recover after signal loss (reproducible, persists through iOS 26.2)

[kawa636r]

I’d like to report and compare notes on a reproducible cellular issue I’ve been able to document on the iPhone 17 series, which has persisted across multiple iOS versions up to 26.2.

This is not a signal coverage complaint, and I’m not talking about temporary slowdowns. This is a failure to recover cellular service after complete signal loss.

Reproduction scenario

This occurs under very normal real-world conditions:

1. Device is on 5G Auto
2. Enter an area with complete signal loss (e.g. basement / underground parking)
3. Device correctly shows No Service
4. Return to an area with known good coverage
5. Device does NOT recover service
6. Cellular remains unusable indefinitely until Airplane Mode is toggled

At no point does it self-recover.

Key observations

Using Field Test Mode (*3001#12345#*):

• The phone often remains logically attached to an LTE cell
• RSRP and RSRQ return to good values
• SINR values become impossible or extreme (e.g. –18 dB, –30 dB, sometimes even one RX chain reporting ~ –40 dB)
• Status bar may still show No Service or frozen connectivity

Only a manual baseband reset (Airplane Mode) restores service.


Why this appears to be a modem / firmware issue?

• The issue is 100% reproducible once triggered
• It persists across iOS versions (tested up to 26.2)
• It occurs even when signal conditions are objectively good
• A second iPhone 17 tested side by side may recover normally, suggesting a latent state-machine issue rather than coverage or carrier problems
• LTE-only mode greatly reduces the likelihood of hitting the bug

This strongly points to a baseband recovery / re-attach failure after total signal loss, likely related to state handling during handover or reacquisition.


What this is NOT

• Not carrier specific (tested with Movistar; behavior consistent across environments)
• Not SIM / eSIM related
• Not a “weak signal” issue
• Not fixed by resets, network settings, or reinstalling iOS

Why I’m posting


I’m not looking for troubleshooting tips or a device replacement discussion.


I want to know:

• Are other iPhone 17 / 17 Pro / 17 Pro Max users seeing the same behavior?
• Especially users who frequently move between no-signal → signal environments
• Has anyone seen improvement in 26.2 or later?

Given that this affects core cellular reliability, I believe it deserves visibility and confirmation.

Suggested test for others

• Enable 5G Auto
• Enter a location with total signal loss
• Return to coverage
• Do not toggle Airplane Mode
• Check Field Test SINR values

If the phone stays offline until manually reset, that’s the issue.

Looking forward to hearing if others can reproduce this.


If enough people are seeing it, it may help get this in front of the right engineering teams.

 

[jz0309]

I’d like to report and compare notes on a reproducible cellular issue I’ve been able to document on the iPhone 17 series, which has persisted across multiple iOS versions up to 26.2.

This is not a signal coverage complaint, and I’m not talking about temporary slowdowns. This is a failure to recover cellular service after complete signal loss.

Reproduction scenario

This occurs under very normal real-world conditions:

1. Device is on 5G Auto
2. Enter an area with complete signal loss (e.g. basement / underground parking)
3. Device correctly shows No Service
4. Return to an area with known good coverage
5. Device does NOT recover service
6. Cellular remains unusable indefinitely until Airplane Mode is toggled

At no point does it self-recover.

Key observations

Using Field Test Mode (*3001#12345#*):

• The phone often remains logically attached to an LTE cell
• RSRP and RSRQ return to good values
• SINR values become impossible or extreme (e.g. –18 dB, –30 dB, sometimes even one RX chain reporting ~ –40 dB)
• Status bar may still show No Service or frozen connectivity

Only a manual baseband reset (Airplane Mode) restores service.


Why this appears to be a modem / firmware issue?

• The issue is 100% reproducible once triggered
• It persists across iOS versions (tested up to 26.2)
• It occurs even when signal conditions are objectively good
• A second iPhone 17 tested side by side may recover normally, suggesting a latent state-machine issue rather than coverage or carrier problems
• LTE-only mode greatly reduces the likelihood of hitting the bug

This strongly points to a baseband recovery / re-attach failure after total signal loss, likely related to state handling during handover or reacquisition.


What this is NOT

• Not carrier specific (tested with Movistar; behavior consistent across environments)
• Not SIM / eSIM related
• Not a “weak signal” issue
• Not fixed by resets, network settings, or reinstalling iOS

Why I’m posting


I’m not looking for troubleshooting tips or a device replacement discussion.


I want to know:

• Are other iPhone 17 / 17 Pro / 17 Pro Max users seeing the same behavior?
• Especially users who frequently move between no-signal → signal environments
• Has anyone seen improvement in 26.2 or later?

Given that this affects core cellular reliability, I believe it deserves visibility and confirmation.

Suggested test for others

• Enable 5G Auto
• Enter a location with total signal loss
• Return to coverage
• Do not toggle Airplane Mode
• Check Field Test SINR values

If the phone stays offline until manually reset, that’s the issue.

Looking forward to hearing if others can reproduce this.


If enough people are seeing it, it may help get this in front of the right engineering teams.

had my 17PM since launch, had a few occasions where I was in a "dead zone" with "No signal" showing, reconnected every time I was back in a covered area, not that I was monitoring this, I just did not have an issue. I'm in the US on TMobile.
You seem convinced it is not carrier related, and also it seems like you are on beta? Have you been able to reproduce this on the released OS version? Have you contacted Apple about this?

 

[kawa636r]

had my 17PM since launch, had a few occasions where I was in a "dead zone" with "No signal" showing, reconnected every time I was back in a covered area, not that I was monitoring this, I just did not have an issue. I'm in the US on TMobile.
You seem convinced it is not carrier related, and also it seems like you are on beta? Have you been able to reproduce this on the released OS version? Have you contacted Apple about this?

yes, since day one on all the firmwares.

i have wrote apple on feedback app and directly on tim cook email, to see if someone is able to escalate this to engineering team.

 

[TheIntruder]

Whatever behavior that's been observed is not universal.

On a recent trip, I surprisingly found myself with "SOS" displayed more than once in the middle of a dense metropolis. Indicating no connection to cell service of any kind.

26.1 on the AT&T 5G network in the U.S.

Each time, signal recovered on its own after moving out of the dead zone.