U0012

Code

LAND ROVER U — Network/User

Medium speed CAN communication bus (+) open

Brand: LAND ROVER

Type: U — Network/User

Views: UK: 22 EN: 28 RU: 27

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Page language: EN

Causes

Open or high‑resistance CAN High (CAN +) wiring or connector
Corroded or disconnected CAN connector or splice
Failed CAN transceiver in one module (module driving CAN High)
Missing or faulty termination resistor(s) on the medium‑speed CAN bus
Aftermarket accessory or recent repair disturbed the bus wiring or connector

Symptoms

Multiple modules on the medium‑speed CAN network show 'no communication' or warning lights
Loss of specific functions controlled by medium CAN (e.g., HVAC, infotainment, instrument cluster, doors)
Intermittent operation of affected systems (communication drops and returns)
Possible DTCs for multiple modules (communication lost)
Vehicle may not enter normal operating modes for features relying on medium CAN

What to check

Read all stored and pending DTCs plus freeze frame with a diagnostic tool (OEM tool preferred)
Use OEM tool to list modules present on medium‑speed CAN and check network status/messages
Visual inspection of medium CAN wiring, connectors, and junctions for damage, corrosion or water ingress
Check fuses and power/ground for modules on the medium‑speed CAN bus
Measure CAN High and CAN Low voltages at accessible connectors with ignition ON, engine OFF
Measure resistance between CAN High and CAN Low (termination resistance) with ignition OFF

Signal parameters

CAN High (recessive): ≈2.5 V (key ON, idle)
CAN Low (recessive): ≈2.5 V (key ON, idle)
Dominant state: CAN High ≈3.5 V, CAN Low ≈1.5 V (during message)
Differential voltage (dominant): ≈2.0 V
Bus termination resistance (between CAN H and CAN L): ≈60 Ω (two 120 Ω in parallel)
Open/very high resistance indicates an open on CAN High or poor connector/continuity

Diagnostic algorithm

Record all communication and network DTCs and note affected modules (use OEM diagnostic tool).
Check module power and ground circuits for modules on the medium CAN bus. Repair any power/ground faults first.
Perform a visual inspection of the medium CAN harness and connectors (look for chafing, broken wires, corrosion, water entry, recent splice/repair).
With ignition ON (engine OFF), measure CAN High and CAN Low voltages at an accessible connector near the affected modules. Compare to expected values (see signal_params).
With ignition OFF, measure DC resistance between CAN H and CAN L at the same connector to verify termination (~60 Ω).
Backprobe and perform continuity/resistance checks from each end of the suspected CAN High conductor to find open/high resistance. Repair any damaged wiring or connectors found.
Isolate segments: disconnect modules/junctions one at a time (as allowed by manufacturer procedure) and re‑measure bus voltages/continuity to locate which segment introduces the open.
Inspect and test termination resistors and replace if missing or out of tolerance.
If wiring and terminations are good, test suspect module transceivers by substituting a known good module or following manufacturer module‑level tests. Replace or reprogram the faulty module as recommended.
After repairs, clear DTCs, recheck module presence and bus messages with the OEM tool, and perform a functional test/road test to confirm repair.
If fault persists, consult wiring diagrams, module harness pinouts, and technical service bulletins for vehicle‑specific faults.

Likely causes

Broken or chafed CAN High conductor in dash or body harness (common stress/chafe points)
Corroded multi‑pin connector at a gateway or junction module
Failed body control / infotainment module transceiver on medium CAN
Water intrusion in a connector or module causing open/high resistance on CAN +
Loose or missing termination resistor after module removal or crash repair

Fault status

⚠️ Status

Medium‑speed CAN bus positive (CAN +) open: loss of continuity or high resistance on the CAN High conductor causing communication faults on the medium CAN network.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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U0012 — Medium speed CAN communication bus (+) open