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Home / DTC / U1003 — General CAN fault: Not characterised

U1003 — General CAN fault: Not characterised

Detailed page for trouble code U1003.

34,332codes
59brands
11,841generic
22,491specific
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Code

U1003

CITROEN U — Network/User

General CAN fault: Not characterised

Brand: CITROEN
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in CAN wiring (CAN H or CAN L)
  • Poor power or ground to one or more control modules
  • Corroded or loose connectors or broken pins in CAN harness
  • Missing or incorrect termination resistor(s) or bus topology fault
  • Failed control module driving the bus into error
  • Water ingress or physical damage to harness or connector

Symptoms

  • Multiple module warning lights or communication warnings on dash
  • Intermittent or permanent loss of certain functions (ABS, airbags, instruments, telematics, etc.)
  • Modules missing from scan tool or ‘No communication’ for one or more nodes
  • Erratic instrument cluster behaviour, flicker or frozen displays
  • Possible no-crank/no-start if powertrain modules lose communication

What to check

  • Read live data and stored U-codes from a capable diagnostic tool; note which modules report communication loss
  • Check battery voltage and condition; ensure charging system healthy
  • Visually inspect CAN connectors and harnesses for corrosion, bent pins, insulation damage or water entry
  • Check fuses and permanent power/ignition supply to the modules on the affected bus
  • Perform a wiggle test of wiring while monitoring communication status with scan tool
  • Check for recent aftermarket installations that tie into CAN, disconnect for test

Signal parameters

  • CAN_H idle ≈ 2.5 V (recessive) and CAN_L idle ≈ 2.5 V; dominant states typically CAN_H ≈ 3.5 V and CAN_L ≈ 1.5 V (typical values vary by vehicle)
  • Differential voltage (CAN_H - CAN_L) — ~0 V at rest, ~2 V during dominant state
  • Bus termination resistance ≈ 60 ohms measured across CAN_H and CAN_L with ignition off
  • Baud rate (vehicle dependent) — common values 125 kbps, 250 kbps, 500 kbps; verify expected rate for segment
  • Error counters / bus-off indications from affected module(s) reported by diagnostic tool

Diagnostic algorithm

  1. Confirm customer complaint and record when/where issue occurs; attempt to reproduce
  2. Use an advanced scan tool to list all modules and note which are not responding or report communication errors
  3. Check battery voltage and main power/ground to all modules on the affected bus; repair any low supply or ground faults
  4. Visually inspect connectors, bellows, and harness routing for damage or corrosion; repair as needed
  5. Measure termination resistance between CAN_H and CAN_L at diagnostic connector — expect ~60 ohms; if open or wrong value, locate missing/shorted terminator
  6. Perform voltmeter checks at relevant module pins for CAN_H and CAN_L idle voltages; compare to expected values
  7. Use an oscilloscope to inspect CAN waveforms for noise, missing dominant bits, bus collisions or distortion while performing functional tests
  8. If a single module is suspected, disconnect it (or its connector) and observe whether the bus returns to normal; replace or re-program module only after wiring checks
  9. Isolate network segments by disconnecting branches or aftermarket devices to find fault location
  10. After repair, clear codes, perform full system scan and road test to verify communications are stable

Likely causes

  • Loose or corroded multi-pin connector at a gateway or central module
  • Damaged CAN pair due to chafing or rodent damage near affected area
  • Faulty ground or low battery voltage causing intermittent module resets
  • Failed module repeatedly sending error frames (bus off condition)
  • Aftermarket device (alarm, stereo, telematics) incorrectly connected to CAN bus

Fault status

⚠️ Status
U1003 — General CAN fault: communication error detected on vehicle CAN network; not characterised to a specific module or signal.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-4.0 hours

Similar codes

U1000 U1001 U0100 U0121 U0073
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Code

U1003

DS U — Network/User

General CAN fault: Not characterised

Brand: DS
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in CAN wiring (CAN H or CAN L)
  • Poor power or ground to one or more control modules
  • Corroded or loose connectors or broken pins in CAN harness
  • Missing or incorrect termination resistor(s) or bus topology fault
  • Failed control module driving the bus into error
  • Water ingress or physical damage to harness or connector

Symptoms

  • Multiple module warning lights or communication warnings on dash
  • Intermittent or permanent loss of certain functions (ABS, airbags, instruments, telematics, etc.)
  • Modules missing from scan tool or ‘No communication’ for one or more nodes
  • Erratic instrument cluster behaviour, flicker or frozen displays
  • Possible no-crank/no-start if powertrain modules lose communication

What to check

  • Read live data and stored U-codes from a capable diagnostic tool; note which modules report communication loss
  • Check battery voltage and condition; ensure charging system healthy
  • Visually inspect CAN connectors and harnesses for corrosion, bent pins, insulation damage or water entry
  • Check fuses and permanent power/ignition supply to the modules on the affected bus
  • Perform a wiggle test of wiring while monitoring communication status with scan tool
  • Check for recent aftermarket installations that tie into CAN, disconnect for test

Signal parameters

  • CAN_H idle ≈ 2.5 V (recessive) and CAN_L idle ≈ 2.5 V; dominant states typically CAN_H ≈ 3.5 V and CAN_L ≈ 1.5 V (typical values vary by vehicle)
  • Differential voltage (CAN_H - CAN_L) — ~0 V at rest, ~2 V during dominant state
  • Bus termination resistance ≈ 60 ohms measured across CAN_H and CAN_L with ignition off
  • Baud rate (vehicle dependent) — common values 125 kbps, 250 kbps, 500 kbps; verify expected rate for segment
  • Error counters / bus-off indications from affected module(s) reported by diagnostic tool

Diagnostic algorithm

  1. Confirm customer complaint and record when/where issue occurs; attempt to reproduce
  2. Use an advanced scan tool to list all modules and note which are not responding or report communication errors
  3. Check battery voltage and main power/ground to all modules on the affected bus; repair any low supply or ground faults
  4. Visually inspect connectors, bellows, and harness routing for damage or corrosion; repair as needed
  5. Measure termination resistance between CAN_H and CAN_L at diagnostic connector — expect ~60 ohms; if open or wrong value, locate missing/shorted terminator
  6. Perform voltmeter checks at relevant module pins for CAN_H and CAN_L idle voltages; compare to expected values
  7. Use an oscilloscope to inspect CAN waveforms for noise, missing dominant bits, bus collisions or distortion while performing functional tests
  8. If a single module is suspected, disconnect it (or its connector) and observe whether the bus returns to normal; replace or re-program module only after wiring checks
  9. Isolate network segments by disconnecting branches or aftermarket devices to find fault location
  10. After repair, clear codes, perform full system scan and road test to verify communications are stable

Likely causes

  • Loose or corroded multi-pin connector at a gateway or central module
  • Damaged CAN pair due to chafing or rodent damage near affected area
  • Faulty ground or low battery voltage causing intermittent module resets
  • Failed module repeatedly sending error frames (bus off condition)
  • Aftermarket device (alarm, stereo, telematics) incorrectly connected to CAN bus

Fault status

⚠️ Status
U1003 — General CAN fault: communication error detected on vehicle CAN network; not characterised to a specific module or signal.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-4.0 hours

Similar codes

U1000 U1001 U0100 U0121 U0073
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Code

U1003

HYUNDAI U — Network/User

Temperature Sensor Signal Error in Head Unit | Lost Communication With TCM (H-CAN)

Brand: HYUNDAI
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in CAN wiring (CAN H or CAN L)
  • Poor power or ground to one or more control modules
  • Corroded or loose connectors or broken pins in CAN harness
  • Missing or incorrect termination resistor(s) or bus topology fault
  • Failed control module driving the bus into error
  • Water ingress or physical damage to harness or connector

Symptoms

  • Multiple module warning lights or communication warnings on dash
  • Intermittent or permanent loss of certain functions (ABS, airbags, instruments, telematics, etc.)
  • Modules missing from scan tool or ‘No communication’ for one or more nodes
  • Erratic instrument cluster behaviour, flicker or frozen displays
  • Possible no-crank/no-start if powertrain modules lose communication

What to check

  • Read live data and stored U-codes from a capable diagnostic tool; note which modules report communication loss
  • Check battery voltage and condition; ensure charging system healthy
  • Visually inspect CAN connectors and harnesses for corrosion, bent pins, insulation damage or water entry
  • Check fuses and permanent power/ignition supply to the modules on the affected bus
  • Perform a wiggle test of wiring while monitoring communication status with scan tool
  • Check for recent aftermarket installations that tie into CAN, disconnect for test

Signal parameters

  • CAN_H idle ≈ 2.5 V (recessive) and CAN_L idle ≈ 2.5 V; dominant states typically CAN_H ≈ 3.5 V and CAN_L ≈ 1.5 V (typical values vary by vehicle)
  • Differential voltage (CAN_H - CAN_L) — ~0 V at rest, ~2 V during dominant state
  • Bus termination resistance ≈ 60 ohms measured across CAN_H and CAN_L with ignition off
  • Baud rate (vehicle dependent) — common values 125 kbps, 250 kbps, 500 kbps; verify expected rate for segment
  • Error counters / bus-off indications from affected module(s) reported by diagnostic tool

Diagnostic algorithm

  1. Confirm customer complaint and record when/where issue occurs; attempt to reproduce
  2. Use an advanced scan tool to list all modules and note which are not responding or report communication errors
  3. Check battery voltage and main power/ground to all modules on the affected bus; repair any low supply or ground faults
  4. Visually inspect connectors, bellows, and harness routing for damage or corrosion; repair as needed
  5. Measure termination resistance between CAN_H and CAN_L at diagnostic connector — expect ~60 ohms; if open or wrong value, locate missing/shorted terminator
  6. Perform voltmeter checks at relevant module pins for CAN_H and CAN_L idle voltages; compare to expected values
  7. Use an oscilloscope to inspect CAN waveforms for noise, missing dominant bits, bus collisions or distortion while performing functional tests
  8. If a single module is suspected, disconnect it (or its connector) and observe whether the bus returns to normal; replace or re-program module only after wiring checks
  9. Isolate network segments by disconnecting branches or aftermarket devices to find fault location
  10. After repair, clear codes, perform full system scan and road test to verify communications are stable

Likely causes

  • Loose or corroded multi-pin connector at a gateway or central module
  • Damaged CAN pair due to chafing or rodent damage near affected area
  • Faulty ground or low battery voltage causing intermittent module resets
  • Failed module repeatedly sending error frames (bus off condition)
  • Aftermarket device (alarm, stereo, telematics) incorrectly connected to CAN bus

Fault status

⚠️ Status
U1003 — General CAN fault: communication error detected on vehicle CAN network; not characterised to a specific module or signal.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-4.0 hours

Similar codes

U1000 U1001 U0100 U0121 U0073
371

Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

HYUNDAI

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
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Code

U1003

LAND ROVER U — Network/User

Clock System

Brand: LAND ROVER
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in CAN wiring (CAN H or CAN L)
  • Poor power or ground to one or more control modules
  • Corroded or loose connectors or broken pins in CAN harness
  • Missing or incorrect termination resistor(s) or bus topology fault
  • Failed control module driving the bus into error
  • Water ingress or physical damage to harness or connector

Symptoms

  • Multiple module warning lights or communication warnings on dash
  • Intermittent or permanent loss of certain functions (ABS, airbags, instruments, telematics, etc.)
  • Modules missing from scan tool or ‘No communication’ for one or more nodes
  • Erratic instrument cluster behaviour, flicker or frozen displays
  • Possible no-crank/no-start if powertrain modules lose communication

What to check

  • Read live data and stored U-codes from a capable diagnostic tool; note which modules report communication loss
  • Check battery voltage and condition; ensure charging system healthy
  • Visually inspect CAN connectors and harnesses for corrosion, bent pins, insulation damage or water entry
  • Check fuses and permanent power/ignition supply to the modules on the affected bus
  • Perform a wiggle test of wiring while monitoring communication status with scan tool
  • Check for recent aftermarket installations that tie into CAN, disconnect for test

Signal parameters

  • CAN_H idle ≈ 2.5 V (recessive) and CAN_L idle ≈ 2.5 V; dominant states typically CAN_H ≈ 3.5 V and CAN_L ≈ 1.5 V (typical values vary by vehicle)
  • Differential voltage (CAN_H - CAN_L) — ~0 V at rest, ~2 V during dominant state
  • Bus termination resistance ≈ 60 ohms measured across CAN_H and CAN_L with ignition off
  • Baud rate (vehicle dependent) — common values 125 kbps, 250 kbps, 500 kbps; verify expected rate for segment
  • Error counters / bus-off indications from affected module(s) reported by diagnostic tool

Diagnostic algorithm

  1. Confirm customer complaint and record when/where issue occurs; attempt to reproduce
  2. Use an advanced scan tool to list all modules and note which are not responding or report communication errors
  3. Check battery voltage and main power/ground to all modules on the affected bus; repair any low supply or ground faults
  4. Visually inspect connectors, bellows, and harness routing for damage or corrosion; repair as needed
  5. Measure termination resistance between CAN_H and CAN_L at diagnostic connector — expect ~60 ohms; if open or wrong value, locate missing/shorted terminator
  6. Perform voltmeter checks at relevant module pins for CAN_H and CAN_L idle voltages; compare to expected values
  7. Use an oscilloscope to inspect CAN waveforms for noise, missing dominant bits, bus collisions or distortion while performing functional tests
  8. If a single module is suspected, disconnect it (or its connector) and observe whether the bus returns to normal; replace or re-program module only after wiring checks
  9. Isolate network segments by disconnecting branches or aftermarket devices to find fault location
  10. After repair, clear codes, perform full system scan and road test to verify communications are stable

Likely causes

  • Loose or corroded multi-pin connector at a gateway or central module
  • Damaged CAN pair due to chafing or rodent damage near affected area
  • Faulty ground or low battery voltage causing intermittent module resets
  • Failed module repeatedly sending error frames (bus off condition)
  • Aftermarket device (alarm, stereo, telematics) incorrectly connected to CAN bus

Fault status

⚠️ Status
U1003 — General CAN fault: communication error detected on vehicle CAN network; not characterised to a specific module or signal.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-4.0 hours

Similar codes

U1000 U1001 U0100 U0121 U0073
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

U1003

Other U — Network/User

SCP (J1850) Invalid or Missing Data for Primary Id

Brand: Other
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in CAN wiring (CAN H or CAN L)
  • Poor power or ground to one or more control modules
  • Corroded or loose connectors or broken pins in CAN harness
  • Missing or incorrect termination resistor(s) or bus topology fault
  • Failed control module driving the bus into error
  • Water ingress or physical damage to harness or connector

Symptoms

  • Multiple module warning lights or communication warnings on dash
  • Intermittent or permanent loss of certain functions (ABS, airbags, instruments, telematics, etc.)
  • Modules missing from scan tool or ‘No communication’ for one or more nodes
  • Erratic instrument cluster behaviour, flicker or frozen displays
  • Possible no-crank/no-start if powertrain modules lose communication

What to check

  • Read live data and stored U-codes from a capable diagnostic tool; note which modules report communication loss
  • Check battery voltage and condition; ensure charging system healthy
  • Visually inspect CAN connectors and harnesses for corrosion, bent pins, insulation damage or water entry
  • Check fuses and permanent power/ignition supply to the modules on the affected bus
  • Perform a wiggle test of wiring while monitoring communication status with scan tool
  • Check for recent aftermarket installations that tie into CAN, disconnect for test

Signal parameters

  • CAN_H idle ≈ 2.5 V (recessive) and CAN_L idle ≈ 2.5 V; dominant states typically CAN_H ≈ 3.5 V and CAN_L ≈ 1.5 V (typical values vary by vehicle)
  • Differential voltage (CAN_H - CAN_L) — ~0 V at rest, ~2 V during dominant state
  • Bus termination resistance ≈ 60 ohms measured across CAN_H and CAN_L with ignition off
  • Baud rate (vehicle dependent) — common values 125 kbps, 250 kbps, 500 kbps; verify expected rate for segment
  • Error counters / bus-off indications from affected module(s) reported by diagnostic tool

Diagnostic algorithm

  1. Confirm customer complaint and record when/where issue occurs; attempt to reproduce
  2. Use an advanced scan tool to list all modules and note which are not responding or report communication errors
  3. Check battery voltage and main power/ground to all modules on the affected bus; repair any low supply or ground faults
  4. Visually inspect connectors, bellows, and harness routing for damage or corrosion; repair as needed
  5. Measure termination resistance between CAN_H and CAN_L at diagnostic connector — expect ~60 ohms; if open or wrong value, locate missing/shorted terminator
  6. Perform voltmeter checks at relevant module pins for CAN_H and CAN_L idle voltages; compare to expected values
  7. Use an oscilloscope to inspect CAN waveforms for noise, missing dominant bits, bus collisions or distortion while performing functional tests
  8. If a single module is suspected, disconnect it (or its connector) and observe whether the bus returns to normal; replace or re-program module only after wiring checks
  9. Isolate network segments by disconnecting branches or aftermarket devices to find fault location
  10. After repair, clear codes, perform full system scan and road test to verify communications are stable

Likely causes

  • Loose or corroded multi-pin connector at a gateway or central module
  • Damaged CAN pair due to chafing or rodent damage near affected area
  • Faulty ground or low battery voltage causing intermittent module resets
  • Failed module repeatedly sending error frames (bus off condition)
  • Aftermarket device (alarm, stereo, telematics) incorrectly connected to CAN bus

Fault status

⚠️ Status
U1003 — General CAN fault: communication error detected on vehicle CAN network; not characterised to a specific module or signal.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-4.0 hours

Similar codes

U1000 U1001 U0100 U0121 U0073
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Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

U1003

PEUGEOT U — Network/User

General CAN fault: Not characterised

Brand: PEUGEOT
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in CAN wiring (CAN H or CAN L)
  • Poor power or ground to one or more control modules
  • Corroded or loose connectors or broken pins in CAN harness
  • Missing or incorrect termination resistor(s) or bus topology fault
  • Failed control module driving the bus into error
  • Water ingress or physical damage to harness or connector

Symptoms

  • Multiple module warning lights or communication warnings on dash
  • Intermittent or permanent loss of certain functions (ABS, airbags, instruments, telematics, etc.)
  • Modules missing from scan tool or ‘No communication’ for one or more nodes
  • Erratic instrument cluster behaviour, flicker or frozen displays
  • Possible no-crank/no-start if powertrain modules lose communication

What to check

  • Read live data and stored U-codes from a capable diagnostic tool; note which modules report communication loss
  • Check battery voltage and condition; ensure charging system healthy
  • Visually inspect CAN connectors and harnesses for corrosion, bent pins, insulation damage or water entry
  • Check fuses and permanent power/ignition supply to the modules on the affected bus
  • Perform a wiggle test of wiring while monitoring communication status with scan tool
  • Check for recent aftermarket installations that tie into CAN, disconnect for test

Signal parameters

  • CAN_H idle ≈ 2.5 V (recessive) and CAN_L idle ≈ 2.5 V; dominant states typically CAN_H ≈ 3.5 V and CAN_L ≈ 1.5 V (typical values vary by vehicle)
  • Differential voltage (CAN_H - CAN_L) — ~0 V at rest, ~2 V during dominant state
  • Bus termination resistance ≈ 60 ohms measured across CAN_H and CAN_L with ignition off
  • Baud rate (vehicle dependent) — common values 125 kbps, 250 kbps, 500 kbps; verify expected rate for segment
  • Error counters / bus-off indications from affected module(s) reported by diagnostic tool

Diagnostic algorithm

  1. Confirm customer complaint and record when/where issue occurs; attempt to reproduce
  2. Use an advanced scan tool to list all modules and note which are not responding or report communication errors
  3. Check battery voltage and main power/ground to all modules on the affected bus; repair any low supply or ground faults
  4. Visually inspect connectors, bellows, and harness routing for damage or corrosion; repair as needed
  5. Measure termination resistance between CAN_H and CAN_L at diagnostic connector — expect ~60 ohms; if open or wrong value, locate missing/shorted terminator
  6. Perform voltmeter checks at relevant module pins for CAN_H and CAN_L idle voltages; compare to expected values
  7. Use an oscilloscope to inspect CAN waveforms for noise, missing dominant bits, bus collisions or distortion while performing functional tests
  8. If a single module is suspected, disconnect it (or its connector) and observe whether the bus returns to normal; replace or re-program module only after wiring checks
  9. Isolate network segments by disconnecting branches or aftermarket devices to find fault location
  10. After repair, clear codes, perform full system scan and road test to verify communications are stable

Likely causes

  • Loose or corroded multi-pin connector at a gateway or central module
  • Damaged CAN pair due to chafing or rodent damage near affected area
  • Faulty ground or low battery voltage causing intermittent module resets
  • Failed module repeatedly sending error frames (bus off condition)
  • Aftermarket device (alarm, stereo, telematics) incorrectly connected to CAN bus

Fault status

⚠️ Status
U1003 — General CAN fault: communication error detected on vehicle CAN network; not characterised to a specific module or signal.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-4.0 hours

Similar codes

U1000 U1001 U0100 U0121 U0073
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

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