LG OLED C2/G2 HDMI Cable Works at 60 Hz but Not 4K 120 Hz

Quick Answer

An HDMI cable can appear perfect at 4K60 yet fail at 4K120 on an LG C2/G2 because the higher-rate mode uses a much more demanding HDMI Fixed Rate Link. Test the source directly into the TV with a short, genuine Ultra High Speed HDMI Cable whose certification label/QR code verifies through the official HDMI program. Remove soundbars, receivers, switches, adapters and wall couplers. Then enable the C2/G2 input's 4K/Deep Color capability and add HDR, 10-bit output and VRR one at a time.

The words “8K,” “48 Gbps,” “gaming,” or “HDMI 2.1” printed in a marketplace title are marketing claims, not the certification itself. Conversely, certification reduces uncertainty but does not make a damaged connector, excessive run or defective sample impossible. A controlled A/B test matters more than brand reputation.

Symptoms of a Marginal High-Rate Link

3840×2160 at 60 Hz is stable, but selecting 120 Hz causes No Signal.

4K120 starts, then briefly blacks out or produces colored sparkles under load.

HDR or 10-bit pushes an otherwise stable 120 Hz link into failure.

A console's 4K/120 capability page changes when an AVR or soundbar is inserted.

Reconnecting the same cable restores the picture temporarily.

One short cable works directly while an in-wall run and coupler do not.

4K120 works at reduced chroma/bit depth but not at the intended format.

Every cable fails on one source or port, while another source works there.

These clues support a link-budget investigation; none alone proves the cable. Source output capability, TV input mode, firmware and intermediaries can produce the same missing mode.

Causes Ordered by Signal Path

Cable performance versus package claims

HDMI Licensing Administrator's Ultra High Speed certification program tests cables for 48G signal performance and electromagnetic-interference requirements. Certified packaging carries the official label with authentication features and a QR code. A listing that merely says “8K60/4K120/48Gbps” has not demonstrated participation.

Certification applies to the cable model/length represented by the label. It is not a guarantee that a counterfeit listing, physically damaged cable or different length behaves identically.

Length, bends and connection count

Loss and reflections become harder to tolerate as rate and passive-copper length rise. Wall plates, female couplers, right-angle adapters and capture devices create additional connection points. A sharp bend or partially seated plug can pass 4K60 yet be marginal at 4K120. For long active optical HDMI, direction, power and return-feature support must match the installation.

Intermediary bandwidth

An AVR or soundbar may advertise HDMI 2.1 features without passing the exact 4K120/HDR/VRR combination. HDMI product version labels do not require every optional feature. Test each device's documented input/output capability rather than assuming its port is “full 2.1.”

Source capability and selected format

PS5 and Xbox Series consoles support 4K120 output, but the connected chain must report it. On PC, the GPU itself needs an appropriate HDMI output; an older card or DisplayPort-to-HDMI adapter may be the limit. Bit depth, chroma, HDR and refresh change required payload and link training.

C2/G2 input configuration

The selected HDMI input must expose its enhanced 4K/Deep Color mode. Firmware, input labeling and Game Optimizer state can affect available options. A disabled high-bandwidth input setting resembles a bad cable because 4K60 may remain available.

Step-by-Step Cable and Link Test

1. Document the failing mode

Record source model, TV port, active resolution, refresh, HDR, bit depth, chroma and VRR. Note whether the failure happens immediately, after a game starts, after standby or only with HDR. “120 Hz does not work” is not enough to reproduce the link state.

2. Verify source capability

On PS5, use Video Output Information and Sony's 4K120 troubleshooting. On Xbox, inspect 4K TV details. On NVIDIA/AMD, confirm the physical HDMI output and driver-supported format. Do not infer HDMI 2.1 from GPU performance; some powerful older cards lack the required native HDMI link.

3. Establish a direct short baseline

Disconnect AVR, soundbar, switch, capture card, adapter, wall plate and extension. Connect source directly to C2/G2 with the console-included cable or a short officially certified Ultra High Speed cable. Seat both ends fully with devices powered down. Select the correct TV input.

If this works, the removed component or long run—not the panel—is the next suspect. Reinsert components one at a time.

4. Authenticate rather than trust keywords

Look for the official Ultra High Speed HDMI Cable certification label on the package and verify its QR code with the official process. A generic QR code linking to a store page is not equivalent. Keep receipt and packaging because defective samples still need exchange.

Do not discard a stable included PS5/Xbox cable merely because another cable has thicker braiding or gold-colored connectors. Construction aesthetics do not establish high-rate performance.

5. Enable the TV's high-bandwidth input

On the installed webOS 22 firmware, enable the relevant HDMI Deep Color/4K function for that input and use Game Optimizer for console testing. Restart the HDMI output after changing it so capabilities are renegotiated. Do not enter a service menu or force unofficial EDID data.

6. Build the mode progressively

Start at 4K60 SDR. Select 4K120 SDR, then add 10-bit/HDR, and finally VRR. Change only one item per run. If 120 Hz alone fails, focus on high-rate capability/link training. If only HDR fails, inspect bit depth/chroma and source settings. If only VRR fails while 4K120 is stable, follow the VRR-specific path.

7. Cross-test one variable

Test the candidate cable on another known 4K120 source/display if available, or test a known-good cable on the same C2/G2 port. Swap TV port only after preserving every other setting. A cable that fails identically across independent high-rate endpoints is strong evidence; one failing TV port across several known-good sources warrants LG support.

8. Retest real installation carefully

If the short direct test passes, rebuild the intended topology. Check each AVR/soundbar port specification and firmware. For in-wall/long runs, use an installation-rated solution designed for required bandwidth and features. Active cables can be directional; ARC/eARC and CEC support must be confirmed separately.

What Not to Conclude

A cable does not improve color, sharpness or HDR when both links deliver the same error-free digital format. More expensive does not mean more accurate. A marginal link can produce errors or lose sync, but it does not normally make a stable picture subtly “more cinematic.”

Likewise, 4K120 output does not prove a game renders 120 unique frames. Panel refresh, game frame rate and HDMI transport are separate. Reducing chroma can be a diagnostic payload reduction, not the final required compromise when the C2/G2 and source both support the desired mode.

Cautions

Power down before repeatedly reseating tight connectors. Do not hang heavy cables from the TV socket or exceed safe bend radius. Avoid blind firmware downgrades, service-menu changes and EDID overrides. Do not replace the TV mainboard before direct certified-cable, alternate-port and independent-source tests.