Hello Dell Team,

I am reporting a problem with Dell Power Button Sync (DPBS) on my Dell Latitude 5420,
Regulatory Model P137G (confirmed on device label).
DPBS completely stopped working immediately after updating to BIOS 1.51.0.

Rollback is blocked, so I cannot return to the previous working BIOS version.

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Affected System

• Model: Dell Latitude 5420
• Regulatory Model: P137G (from bottom label)
• BIOS Version: 1.51.0
• Rollback Status: Rollback Blocked (cannot downgrade)
• OS: Windows 11 25H2
• Monitor: Dell C2722DE (supports DPBS — listed in Dell KB)
• Connection: USB‑C ↔ USB‑C (Power Delivery + DisplayPort Alt Mode)
• DPBS Compatibility: Confirmed by Dell KB article
  (DPBS supported on C2722DE and Latitude 5420)

Before the BIOS update, DPBS worked perfectly for a long time.

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Problem Description

When using the Dell C2722DE monitor, pressing the monitor’s power button should turn on / wake the laptop via USB‑C.
This functionality stopped working after BIOS 1.51.0.

Now:

• USB‑C Power Delivery works
• Video output works
• Monitor USB hub works
• UCSI device is present again
• All drivers are correctly installed
• BUT DPBS does not trigger power‑on or wake at all

The monitor's power button now has zero effect on system wake or startup.

The same monitor still works normally with other Dell systems, confirming the issue is specific to Latitude 5420 BIOS 1.51.0.

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What I Have Already Tried (unsuccessful)

Drivers reinstalled

• Intel Chipset Device Software
• Intel Serial IO
• Intel Management Engine Components
• Intel Thunderbolt Driver
• USB‑C PD / UCSI stack restored
• All Windows ACPI power settings reset

Firmware

• Intel ME FW updated (via BIOS package)
• Monitor firmware updated (via Dell Display Manager)
• Thunderbolt firmware checked (no separate payload for P137G platform)

Resets

• Full UCSI restore
• RTC reset
• Deep system shutdown
• USB‑C re‑enumeration
• DPBS still not working

None of these helped.

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Analysis

Based on Dell documentation, DPBS functionality depends on the platform behavior and OS interaction.

Since:

• BIOS rollback is blocked
• All drivers and firmware are updated
• UCSI is functioning
• DPBS worked before BIOS 1.51.0
• No hardware issues
• Other laptops still work with the same monitor

This strongly suggests a regression in the Embedded Controller (EC) firmware inside BIOS 1.51.0, affecting USB‑C wake signaling required for DPBS.

This behavior only occurs on the Latitude 5420, not on other systems (e.g., Latitude 5450 tested with the same monitor).

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Request to Dell Engineering

Please escalate this case to the BIOS/EC engineering team.

I kindly request:

1. Confirmation whether BIOS 1.51.0 introduced changes to EC that affect USB‑C wake / DPBS behavior.
2. A fix in a future BIOS version or an internal hotfix to restore DPBS functionality.
3. Guidance on how to reinitialize EC / USB‑C wake routing, since RTC reset does NOT reset EC on this model.
4. Information whether a Thunderbolt firmware payload for Latitude 5420 (P137G) exists internally, as none is available for download.

DPBS is an important feature for my workflow when using Dell C2722DE.

Thank you.