C1D20

Code

LAND ROVER C — Chassis

Body Control Module: CAN Communication Fault

Brand: LAND ROVER

Type: C — Chassis

Views: UK: 14 EN: 20 RU: 17

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Page language: EN

Causes

Open, short, or high resistance in CAN High/Low wiring or connectors
Corroded or loose BCM connector or pins
Failed BCM CAN transceiver or internal BCM fault
Missing, shorted, or incorrect termination resistor(s) on the CAN bus
A module on the bus causing bus-off or heavy error frames (including aftermarket devices)
Software/configuration mismatch or corrupted module programming

Symptoms

Multiple modules not responding or intermittent communication with scan tool
Warning lights or instrument cluster errors related to body systems
Non-functioning or intermittent central locking, lighting, wipers, windows, or other BCM-controlled features
Other modules reporting U-codes or communication timeouts
Possible fail-safe modes in dependent modules or vehicle won’t perform certain functions

What to check

Use a diagnostic scan tool to read C1D20 and any related U-codes; record freeze-frame, timestamps, and related modules not responding
Check for other stored communication codes (U0100, U0073, etc.) and note distance in time between events
Visually inspect BCM connector, pins, and harness for corrosion, water ingress, bent pins, or damage
Check for recent aftermarket installations or repairs that tapped into the CAN bus
Measure voltage at BCM power/ground pins to confirm stable supply and ground
Measure CAN High and CAN Low voltages with key on (see signal_params) and check terminal resistance between CAN H and CAN L (~60 ohms)

Signal parameters

CAN_H idle (recessive) ≈ 2.5 V (typical range 2.3–2.7 V), dominant ≈ 3.5 V
CAN_L idle (recessive) ≈ 2.5 V (typical range 2.3–2.7 V), dominant ≈ 1.5 V
Differential voltage recessive ≈ 0 V, dominant ≈ 1.5–2.0 V
Bus resistance between CAN_H and CAN_L (two terminators in parallel) ≈ 60 Ω (±10%)
Typical bitrates for vehicle networks: 500 kb/s or 250 kb/s (confirm network speed with factory data)
Watch error counters and bus-off flags in scan tool: TX/RX error counts, bus-off state, and message loss percentages

Diagnostic algorithm

Connect a capable OEM-level scan tool. Read and record C1D20 and any related communication codes. Note which modules are not responding and any time stamps.
Inspect BCM connector and wiring for corrosion, water ingress, physical damage, or bent pins. Repair any visible damage and reconnect securely.
Verify BCM power and ground circuits are within specification. Low supply voltage or poor ground can cause transceiver faults.
With ignition ON, measure CAN_H and CAN_L at the BCM with a DMM. Confirm idle voltages per signal_params. Check resistance between CAN_H and CAN_L (~60 Ω).
If voltages or resistance are out of range, isolate sections of the bus: disconnect connectors or modules systematically to find where the short/open is located. After each disconnect, re-check voltages and resistance.
Use an oscilloscope (preferred) to view CAN waveforms at the BCM while observing live traffic on the scan tool. Look for stuck dominants, excessive noise, or malformed frames.
Perform wiggle tests on harnesses while monitoring live data to reproduce intermittent faults. Inspect and repair any failure points found.
If physical wiring and network integrity are confirmed, check for software/firmware mismatches. Reflash or update BCM and other module software per manufacturer procedures and clear codes.
If the bus is healthy but the BCM still reports faults and other modules respond normally, consider BCM internal fault (failed transceiver). Replace BCM or repair transceiver per service manual and reprogram as required.
After repair, clear codes, and verify normal network operation under various operating conditions.

Likely causes

Damaged or corroded BCM connector/harness at BCM
Open/short on CAN H or CAN L near BCM
Failed CAN transceiver inside BCM
Missing or shorted termination resistor(s) in the network
Faulty aftermarket module or recently-installed accessory causing bus errors

Fault status

⚠️ Status

Body Control Module reports CAN communication fault (message timeout, CRC/frame errors, or bus-off) on the vehicle CAN network.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours

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