Troubleshooting
Cellular Troubleshooting
Cellular Troubleshooting in industrial control systems — covering 5 topic areas in the CurryControls.com controls and automation knowledge hub.
Written guides in this section
Full references, procedures, and diagnostic guides published under Cellular Troubleshooting.
Cellular Modem Will Not Register
A modem that never attaches to the network: a module not activated, provisioned, or suspended; unsupported bands or a network shutdown; no antenna or coverage; a wrong access point name; or a reset modem. Reading the registration state and asking the carrier.
8 min readUpdated Sep 5, 2026
Frequent Reconnects
A cellular site that connects, drops, and reconnects: a weak signal at the cell edge, tower handoffs, idle session teardown, a NAT timeout that needs a keepalive, a firmware fault, a sagging supply, or an antenna problem. Settings that keep sessions up.
8 min readUpdated Sep 5, 2026
Data Plan or APN Problems
A modem that registers but has no data, or runs out mid-month: a wrong or changed APN, a capped or throttled plan, a module on the wrong plan or network, a missing static address, or polling that uses more data than planned. Sizing a plan, cutting traffic.
8 min readUpdated Sep 5, 2026
VPN Tunnel Drops
The modem is up and the tunnel keeps dropping: a changing cellular address, keepalive longer than the carrier timeout, mismatched rekey lifetimes, an oversized MTU, a modem reconnecting under the tunnel, a full concentrator, or a clock or certificate fault.
9 min readUpdated Sep 5, 2026
Weak Cellular Signal
A modem at the edge of coverage: the signal readings that matter, an antenna inside a metal enclosure or vault, the wrong band, a damaged antenna or lossy coax, a tower or carrier change, and fixes from a mast antenna to a directional one or a new medium.
8 min readUpdated Sep 5, 2026
Topics in this area
Cellular Modem Will Not Register
Cellular Modem Will Not Register — practical reference notes for controls engineers, integrators, and technicians working with cellular troubleshooting.
Frequent Reconnects
Frequent Reconnects — practical reference notes for controls engineers, integrators, and technicians working with cellular troubleshooting.
Data Plan Or APN Problems
Data Plan Or APN Problems — practical reference notes for controls engineers, integrators, and technicians working with cellular troubleshooting.
VPN Tunnel Drops
VPN Tunnel Drops — practical reference notes for controls engineers, integrators, and technicians working with cellular troubleshooting.
Weak Cellular Signal
Weak Cellular Signal — practical reference notes for controls engineers, integrators, and technicians working with cellular troubleshooting.
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