Code
U012B
Generic
U — Network/User
Lost Communication With Chassis Control Module B
Views:
UK: 12
EN: 27
RU: 25
AI status
Completed
Completed
100%
Causes
- Open or shorted CAN/LIN network wiring between modules
- Faulty or intermittent connector(s) at the Chassis Control Module B
- Blown fuse or loss of module power or ground
- Failed Chassis Control Module B
- Network bus termination missing or incorrect (open/failed 120 Ω terminators)
- Other module driving the bus incorrectly (short to battery/chassis, bus transceiver fault)
Symptoms
- One or more chassis/ABS/stability/traction warning lights illuminated
- Reduced or disabled ABS, traction control, or stability functions
- Scanner shows “no response” or blank data for Chassis Control Module B
- Multiple related U-codes or communication DTCs stored in other modules
- Intermittent faults or loss of function that can come and go as wiring moves
What to check
- Use a scan tool to confirm U012B and list other stored communication DTCs
- Verify battery voltage (key on and cranking) and check charging system
- Inspect fuses and fusible links for the chassis module power circuit
- Visually inspect connectors and wiring to the chassis module for corrosion, bent pins, or damage
- Check for proper ground(s) at the module — measure resistance to chassis (
- Measure CAN_H and CAN_L voltages at the module connector with ignition on
Signal parameters
- Idle (recessive) voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (typical)
- Dominant bus voltages during transmission: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V)
- Termination: two 120 Ω resistors in parallel (≈60 Ω total) across CAN_H and CAN_L
- Common high-speed CAN bit rates commonly used: 500 kb/s or 250 kb/s (verify vehicle-specific rate)
- Expected DC resistance across bus with ignition ON: approx 55–70 ohms (varies with vehicle design)
- Module supply voltage: battery voltage at module power pin (within ~0.5 V of battery with key on)
Diagnostic algorithm
- Read and record all DTCs from all modules to identify related network faults.
- Verify vehicle battery voltage and charging system health; low voltage can cause communication errors.
- Inspect fuses and relays for the chassis module supply; replace any blown fuses and re-check.
- Visually inspect wiring and connectors at the chassis module and along the bus for damage, corrosion, or loose pins.
- Verify good ground(s) at the chassis module (measure resistance to chassis).
- With ignition ON, measure CAN_H and CAN_L at the module connector: confirm recessive voltages (~2.5 V) and dominant levels during activity. If no activity, attempt to wake the network with a scan tool or by turning ignition ON/OFF.
- Measure resistance between CAN_H and CAN_L with ignition OFF; expect approx 60 Ω (two terminators). An open or very high reading indicates missing termination; very low indicates a short.
- Use a lab scope or CAN analyzer to capture bus traffic. Look for missing frames from the chassis module, corrupted frames, or a node holding the bus dominant.
- If another module is suspected, disconnect that module (one at a time) while monitoring the bus to isolate a shorting node. Note safety implications and system behaviour before disconnecting safety-critical modules.
- If wiring and bus health are good, check for correct software/calibration of the chassis module; reflash or update software if a mismatch is suspected.
- If evidence points to a failed module (no power/ground issues, correct bus, no wiring short), replace the chassis control module and program/configure per manufacturer procedure.
- Clear codes and test drive to verify repair. Re-scan all modules to ensure no further U-codes are present.
Likely causes
- Corroded or disconnected connector at the chassis module (power, ground or bus pins)
- Damaged CAN-H or CAN-L wiring (pinched, chafed, or crushed harness)
- Blown fuse supplying the chassis module
- Failed CAN transceiver inside the chassis module or another node on the same bus
- Missing/failed termination resistor(s) or short between CAN lines
Fault status
Status
Lost Communication With Chassis Control Module B — no responses from the module on the vehicle communications network.
Repair difficulty: Medium
Diagnostic time: 1-4 hours
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Code
U012B
LAND ROVER
U — Network/User
Lost communication with the chassis control module B
Views:
UK: 3
EN: 6
RU: 8
AI status
Completed
Completed
100%
Causes
- Open or shorted CAN/LIN network wiring between modules
- Faulty or intermittent connector(s) at the Chassis Control Module B
- Blown fuse or loss of module power or ground
- Failed Chassis Control Module B
- Network bus termination missing or incorrect (open/failed 120 Ω terminators)
- Other module driving the bus incorrectly (short to battery/chassis, bus transceiver fault)
Symptoms
- One or more chassis/ABS/stability/traction warning lights illuminated
- Reduced or disabled ABS, traction control, or stability functions
- Scanner shows “no response” or blank data for Chassis Control Module B
- Multiple related U-codes or communication DTCs stored in other modules
- Intermittent faults or loss of function that can come and go as wiring moves
What to check
- Use a scan tool to confirm U012B and list other stored communication DTCs
- Verify battery voltage (key on and cranking) and check charging system
- Inspect fuses and fusible links for the chassis module power circuit
- Visually inspect connectors and wiring to the chassis module for corrosion, bent pins, or damage
- Check for proper ground(s) at the module — measure resistance to chassis (
- Measure CAN_H and CAN_L voltages at the module connector with ignition on
Signal parameters
- Idle (recessive) voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (typical)
- Dominant bus voltages during transmission: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V)
- Termination: two 120 Ω resistors in parallel (≈60 Ω total) across CAN_H and CAN_L
- Common high-speed CAN bit rates commonly used: 500 kb/s or 250 kb/s (verify vehicle-specific rate)
- Expected DC resistance across bus with ignition ON: approx 55–70 ohms (varies with vehicle design)
- Module supply voltage: battery voltage at module power pin (within ~0.5 V of battery with key on)
Diagnostic algorithm
- Read and record all DTCs from all modules to identify related network faults.
- Verify vehicle battery voltage and charging system health; low voltage can cause communication errors.
- Inspect fuses and relays for the chassis module supply; replace any blown fuses and re-check.
- Visually inspect wiring and connectors at the chassis module and along the bus for damage, corrosion, or loose pins.
- Verify good ground(s) at the chassis module (measure resistance to chassis).
- With ignition ON, measure CAN_H and CAN_L at the module connector: confirm recessive voltages (~2.5 V) and dominant levels during activity. If no activity, attempt to wake the network with a scan tool or by turning ignition ON/OFF.
- Measure resistance between CAN_H and CAN_L with ignition OFF; expect approx 60 Ω (two terminators). An open or very high reading indicates missing termination; very low indicates a short.
- Use a lab scope or CAN analyzer to capture bus traffic. Look for missing frames from the chassis module, corrupted frames, or a node holding the bus dominant.
- If another module is suspected, disconnect that module (one at a time) while monitoring the bus to isolate a shorting node. Note safety implications and system behaviour before disconnecting safety-critical modules.
- If wiring and bus health are good, check for correct software/calibration of the chassis module; reflash or update software if a mismatch is suspected.
- If evidence points to a failed module (no power/ground issues, correct bus, no wiring short), replace the chassis control module and program/configure per manufacturer procedure.
- Clear codes and test drive to verify repair. Re-scan all modules to ensure no further U-codes are present.
Likely causes
- Corroded or disconnected connector at the chassis module (power, ground or bus pins)
- Damaged CAN-H or CAN-L wiring (pinched, chafed, or crushed harness)
- Blown fuse supplying the chassis module
- Failed CAN transceiver inside the chassis module or another node on the same bus
- Missing/failed termination resistor(s) or short between CAN lines
Fault status
Status
Lost Communication With Chassis Control Module B — no responses from the module on the vehicle communications network.
Repair difficulty: Medium
Diagnostic time: 1-4 hours
Similar codes
Workshop Manuals
Repair manuals for LAND ROVER
3
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)
Workshop Manual199,00 UAH
Land Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop Manual199,00 UAH
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
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👎 Dislike
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Send to email