Modem / cellular

Modem / cellular (field intro)

Cellular backhaul is why a healthy power stage still looks “down” on the CSMS. This category covers LTE/5G modems, SIM/APN paths, antenna placement, and the DNS/TLS failures that present as Heartbeat timeouts or soft-offline stalls.

What you are diagnosing

Most modem tickets are not “radio dead.” They are APN mismatch after a SIM swap, DNS that cannot resolve the CSMS host, TLS/cert drift after a board change, NAT keepalive killing the WebSocket, or RSSI that collapses when the cabinet door is closed. Photograph the modem LEDs, pull the last BootNotification/Heartbeat window, and decide whether the charger can reach the CSMS at all before you RMA a control board.

How it presents

• Station Available locally, Cloud/CSMS offline
• Heartbeat gaps with intermittent sessions
• Authorize failures while FreeVend still works (money path ≠ RF path—but both can share the modem)
• Multi-stall pads where only cabinets with poor antenna runs fail

Start with NET-C01 DNS, OCPP-F02 Heartbeat, and MDM-RSSI. Broader map: OCPP Faulted triage.

Field discipline

1. Confirm SIM active and APN matches carrier/CPO docs.
2. Resolve CSMS hostname from the cabinet network path.
3. Check RSSI/RSRP with door closed (cabinet attenuation is real).
4. After modem or SBC swap, re-enter CSMS URL, chargeBoxIdentity, and certs.
5. Escalate to site IT when firewall rules block outbound 443/wss to the CSMS.

Do not index every weak RSSI as a new antenna part until DNS and APN are proven. Browse faults in this category below.

Antenna and cabinet reality

Metal cabinets attenuate. An RSSI that looks fine with the door open can collapse shut. Route antennas per OEM; avoid coiling spare cable against the sheet metal. After civil work, check that landscapers did not bend or bury the antenna whip.

What not to do

Do not RMA the SBC because Cloud is red before APN/DNS/TLS are proven. Do not assume one working stall proves the pad’s backhaul—antenna runs differ per cabinet.