Code
U0119
Generic
U — Network/User
Lost Communication With Fuel Cell Control Module
AI status
Completed
Completed
100%
Causes
- Open or shorted CAN wiring between FCM and vehicle network
- Faulty or corroded connector(s) at the FCM or junction points
- Loss of power or ground to the Fuel Cell Control Module
- Missing or incorrect CAN termination (open or double-terminated bus)
- High CAN bus error rate or bus flooding by another module
- Defective Fuel Cell Control Module or internal software fault
Symptoms
- Warning or advisory message about fuel cell or propulsion system
- Reduced propulsion, limp-home mode, or loss of fuel cell control functions
- Inability to read fuel cell data or DTCs with a scan tool
- Other modules reporting communication timeouts or related U-codes
- Possible inability to start or reduced charging/control of the fuel cell system
What to check
- Connect an MVCI/scanner and confirm U0119 and any related U-codes or freeze frame data
- Verify battery voltage is within spec and observe during engine/vehicle start
- Visually inspect connectors, pins, and wiring at the FCM and any intermediate junctions for corrosion, damage, or disconnection
- Check fuses and relays that supply power to the FCM
- Scan network for other modules reporting communication errors
- Measure CAN bus idle voltages at a known-good connector (CAN_H ~2.5V, CAN_L ~2.5V) and verify differential behavior with activity
Signal parameters
- Network type: Controller Area Network (CAN) – vehicle-specific (single or dual CAN domains)
- Expected message frequency: periodic FCM status messages (varies by manufacturer, typically 10–1000 ms intervals)
- Idle voltages: CAN_H ~2.5 V, CAN_L ~2.5 V (differential ~0 V when idle); dominant state ~CAN_H high, CAN_L low
- Termination: ~60 Ω measured between CAN_H and CAN_L at a single connection point (two 120 Ω resistors in parallel)
- Typical data: FCM module ID messages, status/operational flags, fault and readiness information (IDs/periods are manufacturer specific)
Diagnostic algorithm
- Record and save all current DTCs and freeze frame data with a scan tool.
- Attempt normal communication with the Fuel Cell Control Module using a dealer-level or capable scan tool. Note whether the module responds and timestamp failures.
- Check vehicle battery voltage and charging system while attempting communication; low voltage can cause module sleep or dropout.
- Visually inspect FCM connectors, backshells, and wiring for corrosion, bent pins, water intrusion, or physical damage; repair as needed.
- Verify power and ground to the FCM: check fuses, relays, and pin side pinout for proper voltage and solid ground with key on and running as required.
- Using a DVOM and then an oscilloscope, check CAN_H and CAN_L at the FCM connector and at a known-good node: verify idle voltages, dominant/recessive transitions, and differential waveform integrity.
- Measure resistance between CAN_H and CAN_L with battery disconnected to verify proper termination (~60 Ω).
- If CAN wiring and termination are good but the FCM does not respond, try waking the module per service procedure (wake via wake line or cycle ignition) and reattempt communication.
- Check for other modules flooding the CAN bus: disconnect suspect modules or isolate CAN segments to see if communication is restored.
- If wiring, power, grounds, and bus integrity are confirmed, update module software if a technical service bulletin (TSB) or calibration update exists, then replace the FCM only after confirming failure.
- Clear codes and re-test to confirm repair. Document the repair path and test drive as required.
Likely causes
- Loss of module supply or ground (fuse, relay, wiring)
- Damaged/loose connector at FCM or intermediate splice
- CAN bus short to battery or ground on CAN_H or CAN_L
- Missing/failed 120 Ω termination resistor or harness cut
- Faulty FCM hardware or corrupted firmware/software
Fault status
Status
Lost Communication With Fuel Cell Control Module — the vehicle network has not received valid CAN messages from the Fuel Cell Control Module for the expected timeout period. This indicates a communication interruption between the FCM and the vehicle network.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Repair manuals
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Code
U0119
HYUNDAI
U — Network/User
Lost Communication With Fuel Cell Control Module
AI status
Completed
Completed
100%
Causes
- Open or shorted CAN wiring between FCM and vehicle network
- Faulty or corroded connector(s) at the FCM or junction points
- Loss of power or ground to the Fuel Cell Control Module
- Missing or incorrect CAN termination (open or double-terminated bus)
- High CAN bus error rate or bus flooding by another module
- Defective Fuel Cell Control Module or internal software fault
Symptoms
- Warning or advisory message about fuel cell or propulsion system
- Reduced propulsion, limp-home mode, or loss of fuel cell control functions
- Inability to read fuel cell data or DTCs with a scan tool
- Other modules reporting communication timeouts or related U-codes
- Possible inability to start or reduced charging/control of the fuel cell system
What to check
- Connect an MVCI/scanner and confirm U0119 and any related U-codes or freeze frame data
- Verify battery voltage is within spec and observe during engine/vehicle start
- Visually inspect connectors, pins, and wiring at the FCM and any intermediate junctions for corrosion, damage, or disconnection
- Check fuses and relays that supply power to the FCM
- Scan network for other modules reporting communication errors
- Measure CAN bus idle voltages at a known-good connector (CAN_H ~2.5V, CAN_L ~2.5V) and verify differential behavior with activity
Signal parameters
- Network type: Controller Area Network (CAN) – vehicle-specific (single or dual CAN domains)
- Expected message frequency: periodic FCM status messages (varies by manufacturer, typically 10–1000 ms intervals)
- Idle voltages: CAN_H ~2.5 V, CAN_L ~2.5 V (differential ~0 V when idle); dominant state ~CAN_H high, CAN_L low
- Termination: ~60 Ω measured between CAN_H and CAN_L at a single connection point (two 120 Ω resistors in parallel)
- Typical data: FCM module ID messages, status/operational flags, fault and readiness information (IDs/periods are manufacturer specific)
Diagnostic algorithm
- Record and save all current DTCs and freeze frame data with a scan tool.
- Attempt normal communication with the Fuel Cell Control Module using a dealer-level or capable scan tool. Note whether the module responds and timestamp failures.
- Check vehicle battery voltage and charging system while attempting communication; low voltage can cause module sleep or dropout.
- Visually inspect FCM connectors, backshells, and wiring for corrosion, bent pins, water intrusion, or physical damage; repair as needed.
- Verify power and ground to the FCM: check fuses, relays, and pin side pinout for proper voltage and solid ground with key on and running as required.
- Using a DVOM and then an oscilloscope, check CAN_H and CAN_L at the FCM connector and at a known-good node: verify idle voltages, dominant/recessive transitions, and differential waveform integrity.
- Measure resistance between CAN_H and CAN_L with battery disconnected to verify proper termination (~60 Ω).
- If CAN wiring and termination are good but the FCM does not respond, try waking the module per service procedure (wake via wake line or cycle ignition) and reattempt communication.
- Check for other modules flooding the CAN bus: disconnect suspect modules or isolate CAN segments to see if communication is restored.
- If wiring, power, grounds, and bus integrity are confirmed, update module software if a technical service bulletin (TSB) or calibration update exists, then replace the FCM only after confirming failure.
- Clear codes and re-test to confirm repair. Document the repair path and test drive as required.
Likely causes
- Loss of module supply or ground (fuse, relay, wiring)
- Damaged/loose connector at FCM or intermediate splice
- CAN bus short to battery or ground on CAN_H or CAN_L
- Missing/failed 120 Ω termination resistor or harness cut
- Faulty FCM hardware or corrupted firmware/software
Fault status
Status
Lost Communication With Fuel Cell Control Module — the vehicle network has not received valid CAN messages from the Fuel Cell Control Module for the expected timeout period. This indicates a communication interruption between the FCM and the vehicle network.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Repair manuals
Manual library for HYUNDAI
371
Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.
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