U101B

Code

LAND ROVER U — Network/User

Communication lost with GSM - multiple bus

Brand: LAND ROVER

Type: U — Network/User

Views: UK: 15 EN: 28 RU: 25

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Page language: EN

Causes

Telematics/GSM module failure
Loss of module power or ground (blown fuse, relay, wiring fault)
Faulty or poorly connected antenna or SIM (carrier) issue
Open/short or high resistance on one or more vehicle data buses (CAN/LIN/MOST)
Corroded/loose connectors at telematics or gateway modules
Software/firmware mismatch or module configuration error

Symptoms

Loss of telematics services (SOS, remote unlock/location, connected apps)
Warning message on instrument cluster or infotainment about telematics/GSM
Related communication DTCs present (other modules reporting lost comms)
Telematics module not present or not responding in diagnostic tool
Intermittent or permanent loss of remote-start/phone functions

What to check

Read all stored/active DTCs from all modules; note freeze frame and related U-codes
Check vehicle battery voltage and charging system before testing
Verify fuses/relays supplying telematics/GSM module and replace if blown
Visually inspect telematics module, connectors, antenna coax and SIM slot for damage or corrosion
Confirm telematics module powers up: measure key supply and ground at module pins
Use diagnostic tool to see if telematics module responds and publishes expected messages on each bus

Signal parameters

CAN bus differential: idle common mode ~2.5 V, dominant differential >1.0 V (CAN_H ~2.5–3.5 V, CAN_L ~1.5–2.5 V depending on state)
Expected CAN termination: ≈60 ohms across CAN_H and CAN_L
Telematics heartbeat/keepalive messages: typically periodic (tool-dependent) — module should transmit/respond regularly
Module supply voltage: stable battery/ignition-dependent 12 V (nominal 11–14 V while cranking/charging)
Ground continuity:

Diagnostic algorithm

Capture complete DTC list from all modules; record U101B occurrence and any other U-codes or B/C/P faults.
Verify battery voltage and health; ensure proper test power before communications testing.
Check and replace any telematics-related fuses and relays; verify module receives 12 V and a clean ground at connector pins.
Use a capable diagnostic tool to query the telematics/GSM module. If the module is not listed, check physical connections and power first.
Inspect antenna coax and SIM slot; reseat SIM and antenna connectors. If vehicle uses embedded SIM, check for corrosion or connector damage.
With ignition on, measure CAN_H and CAN_L at the module connector and at the gateway. Confirm idle voltages and differential; check termination resistance with ignition off.
If bus voltages or termination are incorrect, trace wiring for opens/shorts and repair; check grounds and chassis bonding points.
If bus is healthy but module does not communicate, attempt module power-cycle/reset and re-scan. Check for available software updates or known module reflash procedures from manufacturer.
If module responds intermittently, perform wiggle/torque tests on harnesses while monitoring bus for dropouts to locate intermittent wiring faults.
If module confirmed dead or irreparably faulty after testing, follow manufacturer procedure for replacement and module programming. After repair, clear codes and verify restored communication and telematics function.

Likely causes

Blown fuse or lost 12 V supply to telematics module
Damaged telematics module or internal GSM modem
Faulty ground connection at telematics unit
CAN bus wiring fault, missing termination or short to battery/ground
Disconnected or damaged antenna coax or SIM not seated
Gateway/module not bridged between buses (software fault)

Fault status

⚠️ Status

Telematics (GSM) module communication lost on multiple networks — telematics services unavailable until communication fault is resolved.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours

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U101B — Communication lost with GSM - multiple bus