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Intermittent DOCSIS T4 timeouts causing confirmed internet outages
I've been experiencing sporadic internet disconnections for several months. The outages typically last a few seconds to under a minute.
My equipment:
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Motorola MB8600 DOCSIS 3.1 modem
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UniFi Cloud Gateway Ultra, directly connected to the modem
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CommScope SV-2G two-way splitter, recently replaced by an Xfinity technician
On November 11, 2026, around 12:31 PM Pacific, my UniFi gateway recorded an internet outage that coincided with a critical T4 timeout in the Motorola modem logs at 12:31:43 PM.
The modem subsequently logged upstream channel errors, including "UCD invalid or channel unusable," and diplexer configuration messages.
Additional observations:
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Downstream power ranges from approximately −5 to −10 dBmV.
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The modem is accumulating substantial downstream uncorrectable codeword errors.
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Upstream transmit power is approximately 44–45 dBmV.
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A previous Xfinity technician replaced the splitter and MoCA filter, but the disconnections continued.
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My main house and attached basement ADU have separate Xfinity accounts and modems, sharing an incoming coax feed.
I'm requesting a technical escalation rather than another basic modem-reset troubleshooting session.
EG
Expert
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123.1K Messages
2 days ago
Minus 10dB is too weak / low, and it may be intermittently fluctuating even lower out of spec. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.
In an effort to try to obtain better connectivity / more wiggle room, check to see if there are any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/reconfigured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage from Home Depot, Target, Wal-Mart, etc. Splitters should be swapped with known to be good / new ones to test.
Also, check the coax cable for any damage such as cuts, nicks, abrasions, kinks, sharp bends, or animal chews.
If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two-way splitter connected directly off of the drop from the street / pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.
Good luck with it !
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XfinityJeniece
Official Employee
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4.6K Messages
11 hours ago
Hey there, @appario, thanks for reaching out through Xfinity Forums regarding your internet connection. I can understand wanting this escalated, especially since you’ve already had a technician replace components and captured a T4 timeout at the same time as the service interruption. The modem logs and recurring disconnects are helpful details. We would be happy to take a look at the connection. Can you please send us a direct message with your full name and your full address?
How to Send Us a Direct Message:
You can see how to send us a direct message here, https://forums.xfinity.com/conversations/guidelines/how-to-direct-messaging-within-the-forum/697ba1e570934d009185c514.
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