U1A39

Code

LAND ROVER U — Network/User

Gateway Communication Fault — Body Control Module

Brand: LAND ROVER

Type: U — Network/User

Views: UK: 34 EN: 44 RU: 32

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Page language: EN

Causes

Corroded, loose, or damaged connector(s) at the BCM/gateway
Blown fuse or loss of ignition/switched power to BCM/gateway
Poor or open ground for BCM/gateway
Damaged CAN/LIN wiring harness (short to power, short to ground, open circuit)
Faulty BCM (internal hardware or firmware fault)
Faulty gateway module or other network gateway device

Symptoms

Malfunctioning interior functions controlled by BCM (central locking, lighting, wipers, windows)
Warning indicators or communications-related messages on dash
Certain modules not responding to diagnostic scanner or intermittent communication with scan tool
Remote/keyless functions inoperative or intermittent
Modules reporting other U-codes or CAN bus errors
Vehicle may enter limp or safe modes for some systems

What to check

Connect a compatible diagnostic tool and read all active and stored U- and manufacturer codes; record freeze frame and related P-codes
Check battery voltage (engine off and cranking) and charge if necessary; ensure stable supply during testing
Visually inspect BCM/gateway connectors for corrosion, bent pins, water ingress, or damage
Check fuses and relays powering the BCM/gateway and replace if blown
Verify good chassis and battery grounds at BCM and nearby grounding points
Scan for additional modules reporting communication faults (helps locate segment or network problem)

Signal parameters

CAN bus idle voltages per node: CAN_H ≈ 2.5 V (nominal), CAN_L ≈ 2.5 V (nominal); differential ~0 V when recessive
Dominant state typical voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Bus termination: network should present approx. 120 Ω between CAN_H and CAN_L at rest (verify across entire bus)
Wake/sleep control or ignition-switched supply should show expected battery voltage when key on and near 0 V when key off (depending on architecture)
Supply and ground at BCM: near battery voltage at fused input, low resistance to ground (

Diagnostic algorithm

Confirm code: connect scan tool, retrieve U1A39 and related codes; document occurrence conditions and freeze frame data.
Clear codes and re-run to see if U1A39 returns; note whether it is permanent, intermittent, or present only after certain events.
Verify battery state-of-charge and charging system; charge battery to full and retest communications.
Visually inspect BCM/gateway connectors, fuses, and ground points. Repair any corrosion or connector damage.
With ignition on, measure supply voltage and ground at BCM/gateway power pins. Repair any power/ground faults before further testing.
Measure CAN_H and CAN_L voltages at the BCM/gateway with a DVM. Expected idle ~2.5 V; if voltages are out of range, isolate wiring/harness for damage.
Use an oscilloscope to inspect CAN waveforms for noise, missing frames, or bus-off conditions while exercising affected systems.
Scan the network for other modules reporting bus errors. If one downstream module is faulting, disconnect it and re-check the bus.
If wiring and external modules check good, verify BCM/gateway software level and programming. Reflash/update per manufacturer procedures if advised.
Replace BCM/gateway only after isolating fault to the module; follow manufacturer coding and programming procedures when installing a new unit.
After repairs, clear codes, perform full network scan and functional checks of BCM-controlled systems, and road-test to confirm fault does not return.

Likely causes

Loose/corroded connector or poor ground at BCM (most common)
CAN bus short or open between BCM and gateway
Blown fuse or loss of supply to BCM/gateway
Faulty BCM or gateway module hardware
Software/configuration issue after battery replacement or module programming

Fault status

⚠️ Status

Gateway reports communication fault with Body Control Module: BCM not responding or network communication corrupted. Further diagnosis required to isolate wiring, power/ground, or module failure.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours

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