MBP M4 Pro chip cannot drive two external monitors at the same time.

I cannot run two monitors external at the same time. I have tried TB5 cables direct to MBP, TB4 cables direct to MBP, TB5 cables to a TB5 dock, TB4 cables to a TB4 dock. USB-C to DP cables, USB-C to HDMI adapters, nothing works. My monitors are ASUS PG32UCDM, I set both to 100Hz 1440P and only one will display.

I’ve plugged one TB5 port and the other HDMI port. I pull the cables the other displays. They both display on my M1 at 1440P 100hz same time. They don’t even work at 1080P/60hz together, lid is always closed.

the docks are both OWC with genuine TB5 and TB4 cables.

I’ve factory reset the MAC, monitors.

anyone any ideas? MAC support says a know issue but I can’t believe it is as it has not blown up on the internet.

i don’t think this could be a monitor issue as they are both the same and both work correctly on an M1 with the pro chip.

MacBook Pro 14″, macOS 15.2

Posted on Jan 17, 2025 3:36 PM

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22 replies

ahearn Author

Level 1

27 points

Jan 17, 2025 5:12 PM in response to Grant Bennet-Alder

Two monitors on 2 cables does not work for me that’s my problem. Only one monitor will display at a time the other shows no signal. Using 2 cables one to each monitor and other end to two TB5 ports on the MBP

ahearn Author

Level 1

27 points

Jan 18, 2025 10:08 AM in response to Grant Bennet-Alder

I understand this. For context (using both monitors simultaneously)

both monitors work fine on my PC using RTX 4080 super over DP/HDMI.

both monitors work fine @ 60Hz on my raspberry pi 5 over mini HDMI/HDMI

both monitors work fine on my 16” M1 MBP with Pro chip @ 100hz on any combination of cables/docks except cables rates for 60Hz only.

both monitors do not work on my M4, through any combination of cables rates/docks.

are there any logs or any other tools that can be run to determine what is happing when a 2nd monitor is plugged into. I’m sure support have access to such tools but doubt a Genius Bar would know.

ahearn Author

Level 1

27 points

Jan 17, 2025 4:52 PM in response to Servant of Cats

I have 16” M1 Pro

ahearn Author

Level 1

27 points

Jan 17, 2025 4:53 PM in response to Servant of Cats

But the both work fine on a M1 Pro chip. Same monitors - same ID or not. Not sure how you find an ID.

Jan 17, 2025 5:16 PM in response to ahearn

then we can talk about connecting two displays to one genuine ThunderBolt-3 or ThunderBolt-5 Dock.

What docks are you considering or attempting to use?

ahearn Author

Level 1

27 points

Jan 17, 2025 6:23 PM in response to Servant of Cats

Nope I just have two monitors plugged in. The power cable and that’s it

ahearn Author

Level 1

27 points

Jan 17, 2025 6:26 PM in response to Grant Bennet-Alder

The docks don’t solve the problem, I am using OWC TB 5 dock that has 4 TB5 ports. Also tried TB4 dock that has 4 TB4 ports - used genuine TB5 cables and genuine TB4 cables.

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MBP M4 Pro chip cannot drive two external monitors at the same time.