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

22 replies

Jan 18, 2025 12:33 PM in response to ahearn

Those comparisons to other systems only tell you that you have no GROSS failures in the displays, and NOTHING more.

The Apple standard for its built-in hardware-accelerated displays, makes them suitable for full-motion video for production/display of cinema-quality video with NO dropped frames, and NO dropouts or partial-blank scan lines due to memory under-runs or other issues.

In addition, most recent versions of MacOS insist that there be NO transmit errors detected by the display. The Mac checks for errors, and if any occur, the display will be blanked.

Low spec cables and too long cables WILL preclude getting a picture on a Mac. if it were a don't care condition, I would not spend my time and energy asking about it.

ahearn Author

Level 1

9 points

Jan 19, 2025 8:55 PM in response to Grant Bennet-Alder

So my solution came from the Genius Bar, they got two monitors running at 60Hz (all their monitors would do) one using TB port other on HDMI. Bizarrely they said the only way to get it to work and at 60Hz on pro and max was TB and HDMI….

They suggested exchanging it even though it was 10days passed the return date. I decided to change it for a Max (they offered an ultra but I’d no idea what that was at that point in time).

Anyway brought it home, plugged it in. And voila, using my single TB5 cable to my TB5 dock, I get my two monitors operational both 1440p and both 120hz.

I’ll test HDR later.

Thanks for the help and apologies if I appeared a bit salty.

Cheers.

ahearn Author

Level 1

9 points

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

I have 16” M1 Pro

ahearn Author

Level 1

9 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

9 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

9 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.

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