Code
U0041
Generic
U — Network/User
Vehicle Communication Bus B (+) High
Views:
UK: 12
EN: 23
RU: 15
AI status
Completed
Completed
100%
Causes
- Short to battery or other power source on Bus B (+) conductor
- Faulty CAN/communication transceiver inside a module
- Damaged, chafed, corroded or pinched wiring or connector on Bus B (+) circuit
- Poor or missing ground/poor module grounds affecting transceiver reference
- Incorrect or missing termination resistor(s) on the bus
- Water intrusion or contamination in connectors causing leakage or unintended voltage
Symptoms
- Multiple modules display communication faults or do not respond to scan tool
- Illuminated communication or network-related warnings on the cluster
- Loss of function for features controlled over Bus B (e.g., infotainment, body, chassis modules)
- Intermittent or permanent fault codes related to network communication
- Unreliable operation of systems when other modules are connected or when wiring is moved
What to check
- Read and record all U-codes and freeze frame data with a capable scan tool; note which modules report loss of communication
- Visual inspection of Bus B wiring harness, connectors, and modules for damage, corrosion, pin damage, or water ingress
- Check for aftermarket devices or recent service work on the bus that could introduce a short
- Measure voltage on Bus B (+) relative to vehicle ground with key ON (engine off) and compare to expected idle values
- Measure voltage between Bus B (+) and Bus B (−) to observe differential behavior
- Measure resistance between Bus B (+) and battery positive with ignition off to detect direct shorts
Signal parameters
- Normal idle (recessive) CAN_H ~2.5 V (typical range ~2.0–3.0 V) and CAN_L ~2.5 V
- Dominant state CAN_H ~3.5 V and CAN_L ~1.5 V (approximate)
- High fault: CAN_H above normal dominant range (can approach battery voltage if shorted to 12 V) — values >3.9–5.0 V indicate an over-voltage condition
- Resistance across CAN_H to CAN_L with network connected should show normal pulsing; static resistance with ignition off and connectors connected should be open/high except for termination (~60 ohm total)
Diagnostic algorithm
- Connect a scan tool and record current network-related U-codes and freeze frame data; note which modules report communication loss
- Perform visual inspection of Bus B wiring, connectors and modules for damage or contamination
- With ignition OFF, disconnect modules on Bus B one at a time and measure resistance between Bus B (+) and battery positive to find a shorted circuit
- With ignition ON (engine off), measure voltage at Bus B (+) relative to ground and compare to expected idle voltage (~2.5 V); also measure Bus B (−) and the differential between them
- If Bus B (+) is high, unplug connectors at harness ends and measure again to determine if the short is in the harness or inside a module
- Check termination resistors by measuring resistance between CAN_H and CAN_L at a connector with the network intact (~60 ohms). If value is incorrect, inspect/replace terminators
- Wiggle/strain-relief test wiring while monitoring voltage to reproduce intermittent faults
- If a single module is identified as the source (pulling the line high), isolate by disconnecting it and see if bus returns to normal; repair or replace the affected module or its transceiver if confirmed
- Repair any damaged wiring, clean/replace corroded connectors, correct termination, and remove improper aftermarket connections
- Clear codes, perform a full power cycle and retest; verify proper communication and no return of U0041
- If diagnostics are inconclusive or module internal faults are suspected, consult manufacturer wiring diagrams and consider module bench testing or replacement
Likely causes
- Shorted Bus B (+) conductor to battery (constant 12 V)
- Failed module CAN transceiver pulling the bus high
- Corroded connector or pin making intermittent high-voltage path
- Missing/incorrect termination resistor causing abnormal biasing
Fault status
Status
Bus B positive (CAN_H) voltage is higher than allowed limits, causing communication errors on Vehicle Communication Bus B. The condition may indicate a short to battery, failed transceiver, or wiring/connector fault.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
U0041
HYUNDAI
U — Network/User
Vehicle Communication Bus B (+) High
Views:
UK: 12
EN: 19
RU: 15
AI status
Completed
Completed
100%
Causes
- Short to battery or other power source on Bus B (+) conductor
- Faulty CAN/communication transceiver inside a module
- Damaged, chafed, corroded or pinched wiring or connector on Bus B (+) circuit
- Poor or missing ground/poor module grounds affecting transceiver reference
- Incorrect or missing termination resistor(s) on the bus
- Water intrusion or contamination in connectors causing leakage or unintended voltage
Symptoms
- Multiple modules display communication faults or do not respond to scan tool
- Illuminated communication or network-related warnings on the cluster
- Loss of function for features controlled over Bus B (e.g., infotainment, body, chassis modules)
- Intermittent or permanent fault codes related to network communication
- Unreliable operation of systems when other modules are connected or when wiring is moved
What to check
- Read and record all U-codes and freeze frame data with a capable scan tool; note which modules report loss of communication
- Visual inspection of Bus B wiring harness, connectors, and modules for damage, corrosion, pin damage, or water ingress
- Check for aftermarket devices or recent service work on the bus that could introduce a short
- Measure voltage on Bus B (+) relative to vehicle ground with key ON (engine off) and compare to expected idle values
- Measure voltage between Bus B (+) and Bus B (−) to observe differential behavior
- Measure resistance between Bus B (+) and battery positive with ignition off to detect direct shorts
Signal parameters
- Normal idle (recessive) CAN_H ~2.5 V (typical range ~2.0–3.0 V) and CAN_L ~2.5 V
- Dominant state CAN_H ~3.5 V and CAN_L ~1.5 V (approximate)
- High fault: CAN_H above normal dominant range (can approach battery voltage if shorted to 12 V) — values >3.9–5.0 V indicate an over-voltage condition
- Resistance across CAN_H to CAN_L with network connected should show normal pulsing; static resistance with ignition off and connectors connected should be open/high except for termination (~60 ohm total)
Diagnostic algorithm
- Connect a scan tool and record current network-related U-codes and freeze frame data; note which modules report communication loss
- Perform visual inspection of Bus B wiring, connectors and modules for damage or contamination
- With ignition OFF, disconnect modules on Bus B one at a time and measure resistance between Bus B (+) and battery positive to find a shorted circuit
- With ignition ON (engine off), measure voltage at Bus B (+) relative to ground and compare to expected idle voltage (~2.5 V); also measure Bus B (−) and the differential between them
- If Bus B (+) is high, unplug connectors at harness ends and measure again to determine if the short is in the harness or inside a module
- Check termination resistors by measuring resistance between CAN_H and CAN_L at a connector with the network intact (~60 ohms). If value is incorrect, inspect/replace terminators
- Wiggle/strain-relief test wiring while monitoring voltage to reproduce intermittent faults
- If a single module is identified as the source (pulling the line high), isolate by disconnecting it and see if bus returns to normal; repair or replace the affected module or its transceiver if confirmed
- Repair any damaged wiring, clean/replace corroded connectors, correct termination, and remove improper aftermarket connections
- Clear codes, perform a full power cycle and retest; verify proper communication and no return of U0041
- If diagnostics are inconclusive or module internal faults are suspected, consult manufacturer wiring diagrams and consider module bench testing or replacement
Likely causes
- Shorted Bus B (+) conductor to battery (constant 12 V)
- Failed module CAN transceiver pulling the bus high
- Corroded connector or pin making intermittent high-voltage path
- Missing/incorrect termination resistor causing abnormal biasing
Fault status
Status
Bus B positive (CAN_H) voltage is higher than allowed limits, causing communication errors on Vehicle Communication Bus B. The condition may indicate a short to battery, failed transceiver, or wiring/connector fault.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
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Code
U0041
MERCEDES-BENZ
U — Network/User
Vehicle Communication Bus B (+) high
Views:
UK: 12
EN: 19
RU: 13
AI status
Completed
Completed
100%
Causes
- Short to battery or other power source on Bus B (+) conductor
- Faulty CAN/communication transceiver inside a module
- Damaged, chafed, corroded or pinched wiring or connector on Bus B (+) circuit
- Poor or missing ground/poor module grounds affecting transceiver reference
- Incorrect or missing termination resistor(s) on the bus
- Water intrusion or contamination in connectors causing leakage or unintended voltage
Symptoms
- Multiple modules display communication faults or do not respond to scan tool
- Illuminated communication or network-related warnings on the cluster
- Loss of function for features controlled over Bus B (e.g., infotainment, body, chassis modules)
- Intermittent or permanent fault codes related to network communication
- Unreliable operation of systems when other modules are connected or when wiring is moved
What to check
- Read and record all U-codes and freeze frame data with a capable scan tool; note which modules report loss of communication
- Visual inspection of Bus B wiring harness, connectors, and modules for damage, corrosion, pin damage, or water ingress
- Check for aftermarket devices or recent service work on the bus that could introduce a short
- Measure voltage on Bus B (+) relative to vehicle ground with key ON (engine off) and compare to expected idle values
- Measure voltage between Bus B (+) and Bus B (−) to observe differential behavior
- Measure resistance between Bus B (+) and battery positive with ignition off to detect direct shorts
Signal parameters
- Normal idle (recessive) CAN_H ~2.5 V (typical range ~2.0–3.0 V) and CAN_L ~2.5 V
- Dominant state CAN_H ~3.5 V and CAN_L ~1.5 V (approximate)
- High fault: CAN_H above normal dominant range (can approach battery voltage if shorted to 12 V) — values >3.9–5.0 V indicate an over-voltage condition
- Resistance across CAN_H to CAN_L with network connected should show normal pulsing; static resistance with ignition off and connectors connected should be open/high except for termination (~60 ohm total)
Diagnostic algorithm
- Connect a scan tool and record current network-related U-codes and freeze frame data; note which modules report communication loss
- Perform visual inspection of Bus B wiring, connectors and modules for damage or contamination
- With ignition OFF, disconnect modules on Bus B one at a time and measure resistance between Bus B (+) and battery positive to find a shorted circuit
- With ignition ON (engine off), measure voltage at Bus B (+) relative to ground and compare to expected idle voltage (~2.5 V); also measure Bus B (−) and the differential between them
- If Bus B (+) is high, unplug connectors at harness ends and measure again to determine if the short is in the harness or inside a module
- Check termination resistors by measuring resistance between CAN_H and CAN_L at a connector with the network intact (~60 ohms). If value is incorrect, inspect/replace terminators
- Wiggle/strain-relief test wiring while monitoring voltage to reproduce intermittent faults
- If a single module is identified as the source (pulling the line high), isolate by disconnecting it and see if bus returns to normal; repair or replace the affected module or its transceiver if confirmed
- Repair any damaged wiring, clean/replace corroded connectors, correct termination, and remove improper aftermarket connections
- Clear codes, perform a full power cycle and retest; verify proper communication and no return of U0041
- If diagnostics are inconclusive or module internal faults are suspected, consult manufacturer wiring diagrams and consider module bench testing or replacement
Likely causes
- Shorted Bus B (+) conductor to battery (constant 12 V)
- Failed module CAN transceiver pulling the bus high
- Corroded connector or pin making intermittent high-voltage path
- Missing/incorrect termination resistor causing abnormal biasing
Fault status
Status
Bus B positive (CAN_H) voltage is higher than allowed limits, causing communication errors on Vehicle Communication Bus B. The condition may indicate a short to battery, failed transceiver, or wiring/connector fault.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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