Direct answer
For the LG M4 wireless OLED TV, correct labeled ports, matching CEC/eARC controls, output format and direct-chain testing matter. First, use the labeled ARC/eARC ports and test PCM/stereo.
What this covers
- LG M4 wireless OLED TV (OLED65/77/83/97M4*)
- Zero Connect box carries external video; isolate box/link versus panel/webOS.
- The specific fault this record addresses: ARC or eARC soundbar audio is not working
What it does not cover
- ×The same symptom on a different LG product line, which has its own record and its own cited source
- ×An on-screen error code whose meaning has not been checked against this exact model's manual
- ×Live electrical, gas, sealed-system, internal battery-cell or structural repair — a technician boundary, not a self-service step
Differential
What actually causes this, and how to tell them apart
These are ordered by how often each one is the answer, not by how easy it is to try. The point of the middle column is that two causes producing the same headline symptom rarely produce the same detail — that detail is what tells you which one you have before you change anything.
- 1
The cable is in the wrong HDMI port
What separates it No audio to the soundbar, with the cable in any port other than the one labelled ARC or eARC.
How to confirm Only one port on the television supports ARC/eARC and it is labelled. This is the most common cause by a wide margin and takes seconds to check.
- 2
HDMI-CEC is disabled on one of the devices
What separates it The soundbar does not power on with the TV, volume control does not pass through, and audio does not route.
How to confirm ARC depends on CEC, and every manufacturer gives it a different name — Anynet+, Bravia Sync, Simplink, VIERA Link. It has to be enabled on both devices.
- 3
The TV's audio output is not set to the ARC device
What separates it Sound continues from the TV speakers with the soundbar connected and powered.
How to confirm Set the audio output explicitly to the HDMI/ARC device rather than relying on automatic detection.
- 4
The cable cannot carry eARC bandwidth
What separates it ARC works but eARC does not, or high-bitrate formats such as Dolby TrueHD or DTS:X fail while compressed formats play.
How to confirm eARC needs substantially more bandwidth than ARC. A cable adequate for ARC can fail at eARC, and manufacturers generally specify a High Speed with Ethernet or Ultra High Speed cable.
- 5
The audio format exceeds what the soundbar supports
What separates it Silence on specific content only, typically Dolby Atmos or DTS:X.
How to confirm Set the TV's output to PCM as a test. If sound returns, the soundbar cannot decode what was being sent.
- 6
The CEC link has stalled
What separates it It worked before and stopped with nothing changed.
How to confirm Power everything off, unplug both devices for 60 seconds, then power the TV on first and the soundbar second. CEC links stall regularly and this clears most.
Before you touch a setting
Record this first — changing settings destroys the evidence
Every item below stops existing the moment a reset, re-pair or settings change is made. Written down first, they are what separates the causes above; recovered afterwards, they are guesswork.
- Which HDMI port the cable is in, and whether that port is the one labelled ARC or eARC.
- Whether HDMI-CEC is enabled on both devices, under whatever name each manufacturer uses.
- Whether the failure is total, or only on specific high-bitrate formats.
- The cable's rating, since eARC requires more bandwidth than ARC.
Confirm the cable is in the port labelled ARC or eARC
ReversibleOnly one port on the television supports it, and this is the single most common cause.
Enable HDMI-CEC on both devices
ReversibleEach manufacturer names it differently — Anynet+, Bravia Sync, Simplink, VIERA Link — and it must be on at both ends.
Set the TV's audio output explicitly to the HDMI/ARC device
ReversibleAutomatic detection frequently fails to switch over.
Set the output format to PCM as a test
ReversibleIf sound returns, the soundbar cannot decode the surround format that was being sent.
Power-cycle both devices with a 60-second unplug, TV powered on first
ReversibleA stalled CEC link is common and this clears most of them.
Model-specific
What is true of this model and not of its siblings
Generic advice for the product line fails here. Each item below is a property of this specific model family that changes which of the steps above apply to you.
- Model scope
- OLED65/77/83/97M4*. Zero Connect box carries external video; isolate box/link versus panel/webOS.
- Panel
- 2024 OLED evo with a Micro Lens Array (MLA) panel and the Alpha 11 processor — essentially the G4 panel. Self-emissive, so bright-window dimming is the Auto Brightness Limiter, not a backlight.
- Zero Connect wireless box
- This is the defining difference: video and audio reach the panel WIRELESSLY from a separate Zero Connect box that holds the ports (three HDMI 2.1 sockets). A 'no signal', dropout or lag fault is very often the box's placement or line of sight to the TV, not the source — keep the box within sight of the panel and clear of obstructions before troubleshooting the input.
- Smart platform
- webOS 24 with the Magic Remote; updates at Settings › Support › Software Update, screen share via AirPlay 2 and Miracast.
- Gaming / HDMI
- Up to 144 Hz with VRR, ALLM, G-Sync and FreeSync — but through the Zero Connect box's three HDMI 2.1 ports, and subject to the wireless link. A signal problem is the box or the wireless path first.
- Symptom boundary
- This record covers LG M4 wireless OLED TV when it ARC or eARC soundbar audio is not working. A different symptom on the same hardware, or this symptom on a different LG product line, has its own record with its own causes and its own cited source.
Stop boundary
When this stops being a self-service repair
Continuing past any one of these costs more than the repair saves — in safety, in warranty, or in evidence a technician needs.
- !Do not use HDMI splitters or switches in an ARC path unless they explicitly support ARC/eARC — most break it entirely.
Evidence ledger
Sources behind this answer
Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.
Where the manufacturer's article stops. LG Support publishes this as "TV and home theater support". Official LG television manuals, webOS support, diagnostics and repair entry point. What that article does not carry is the model boundary — it is written for a product line, and OLED65/77/83/97M4* is the scope applied here. Where a control label, terminal, indicator pattern or reset sequence differs on your unit, the manual for that exact model is the authority, not this page and not the article.
Exact questions
Common follow-ups
My LG M4 keeps losing signal or looks laggy.+
The M4 sends the picture wirelessly from its Zero Connect box to the panel, so the first thing to check is the box: it must be within line of sight of the TV, within the stated range, and clear of obstructions and interference. Reposition the box and confirm the wireless link before you suspect the console, PC or cable — the sources plug into the box, not the TV.
How many HDMI ports does the LG M4 have?+
Three HDMI 2.1 ports, all on the Zero Connect box rather than on the TV itself. Everything connects to the box, which then transmits to the panel wirelessly, so port and signal troubleshooting happens at the box.
My soundbar gets no audio over ARC.+
Check which HDMI port the cable is in first. Only one port on the television supports ARC or eARC, and it is labelled — a cable in any other port gives exactly this symptom, and it is the most common cause by a wide margin. After that, make sure HDMI-CEC is enabled on both devices; every brand calls it something different.
ARC works but eARC doesn't.+
That is almost always the cable. eARC carries far more bandwidth than ARC to support uncompressed and object-based formats, so a cable that is perfectly adequate for ARC can fail at eARC. Manufacturers typically specify a High Speed with Ethernet or Ultra High Speed cable for it.
Does this answer apply to every LG model?+
No. It is scoped to OLED65/77/83/97M4*. Zero Connect box carries external video; isolate box/link versus panel/webOS.
What should I record before troubleshooting eARC or ARC or soundbar?+
Record the complete model identifier, exact message or indicator, software/firmware where visible, the operating stage and what still works.
Why is a factory reset not the first step?+
A reset can erase accounts, networks, maps, schedules or preferences without distinguishing eARC, ARC, soundbar. The ordered checks preserve that evidence.
When should I stop and use qualified service?+
Stop for hot ports, electrical noise, sparks or receiver protection.
Answer for the exact device and software version shown above.