U100A

Code

LAND ROVER U — Network/User

CAN Bus A Communication Fault

Brand: LAND ROVER

Type: U — Network/User

Views: UK: 27 EN: 23 RU: 20

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Page language: EN

Causes

Open or short in CAN High or CAN Low wiring
Corroded, loose, or damaged connector at a module or junction
Failed control module driving the CAN A bus
Missing or incorrect termination resistor(s)
Low battery voltage or poor ground connection
Water ingress or physical damage to harness

Symptoms

MIL or multiple warning lights illuminated
One or more modules show 'no communication' or missing
Intermittent or permanent loss of features (e.g., instrument cluster, ABS, infotainment)
Erratic module behavior or random DTCs
Possible crank no-start if essential ECU lost
Reduced functionality while driving or failure of convenience systems

What to check

Read all modules with a dealer-level scan tool; note which nodes are missing and related U-codes
Check battery voltage and chassis ground quality; ensure proper supply (12.0–14.5 V) during testing
Visually inspect CAN A wiring, connectors, and junctions for damage or corrosion
Perform a wiggle test of harnesses and connectors while monitoring bus activity
Measure bus termination resistance across CAN High and CAN Low (approx. 60 Ω with key off)
Use an oscilloscope or CAN bus analyzer to view CAN_H/CAN_L waveforms and message traffic

Signal parameters

Typical recessive voltage: both CAN_H and CAN_L ≈ 2.5 V (idle)
Typical dominant voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Expected differential voltage on dominant bits ≈ 1.5–2.5 V
Typical termination: two 120 Ω resistors in parallel ≈ 60 Ω across CAN_H and CAN_L
Common bit rates: 125 kbps, 250 kbps, 500 kbps (verify vehicle-specific bus speed)
Abnormal signs: constant dominant state, no transitions, excessive noise, or missing messages

Diagnostic algorithm

Record freeze-frame and all stored U and P codes. Note which modules are not present on the bus.
Verify battery voltage and main ground connections; charge battery or support with a diagnostic supply if low.
Inspect visually at major CAN A connectors and common junctions (near gateway, BCM, instrument cluster) for corrosion or damage.
With key on, use a scan tool to monitor CAN bus live data and node presence. Identify which ECU(s) are missing or throwing errors.
Measure DC resistance between CAN_H and CAN_L at a convenient connector with ignition off — expect ≈ 60 Ω. If open or very high, locate open termination.
Probe CAN_H and CAN_L with an oscilloscope while exercising bus traffic; look for proper recessive/dominant voltages, clean square-ish waveforms, and expected message activity.
Isolate sections: disconnect suspected module(s) or branch wiring (one at a time) to see if bus recovers. Use caution — disconnecting some modules may affect vehicle safety systems.
Repair any damaged wiring, connectors or corrosion found. Replace faulty termination or install missing resistor per vehicle specification.
If a module is confirmed faulty (bus recovers when module disconnected), replace module and re-test.
After repairs, clear codes, verify communication to all modules, and perform a road test to ensure no recurrence.

Likely causes

Damaged connector or wiring at a CAN junction or gateway
Missing/failed termination (open 120 Ω resistor or unplugged ECU)
Module on CAN A has failed and pulled the bus off
Low vehicle battery voltage or poor ground affecting node transceivers
Corrosion or water-damaged harness in known moisture areas

Fault status

⚠️ Status

CAN Bus A communication fault — lost or corrupted communication on CAN network A; modules may be offline or intermittent.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5 - 4.0 hours

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