Code
C1D20
LAND ROVER
C — Chassis
Body Control Module: CAN Communication Fault
Views:
UK: 5
EN: 5
RU: 4
AI status
Completed
Completed
100%
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
Similar codes
Workshop Manuals
Repair manuals for LAND ROVER
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Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop Manual199,00 UAH
Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
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Land Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop Manual199,00 UAH
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