Code
U0100
AUDI
U — Network/User
A faulty PCM, A problem with the control module circuit, A problem with the CAN bus
Views:
UK: 61
EN: 106
RU: 94
AI status
Completed
Completed
100%
Causes
- Failed or intermittent PCM/ECM
- Open, shorted or high-resistance CAN bus wiring (CAN_H/CAN_L)
- Poor power or ground to the PCM (blown fuse, bad ground, corroded connector)
- Disconnected, corroded or damaged connector pins at the PCM or junctions
- Missing or incorrect termination (open or shorted 120Ω resistors)
- Software/firmware mismatch or corrupted PCM software
Symptoms
- No communication with PCM on an OBD-II scanner (scanner shows 'NO COMM' or times out)
- Multiple modules show communication-related DTCs
- Engine may not crank or start, or exhibits limp-home mode
- Malfunction Indicator Lamp (MIL) or other warning lights
- Intermittent faults or total loss of drivetrain functions
- Reduced or no data from PCM on live-data stream (RPM, engine load, sensors)
What to check
- Verify battery voltage and condition (12.4–12.8 V at rest). Check while cranking if needed.
- Scan all modules and note additional U-codes; record freeze-frame and freeze DTC times.
- Visually inspect PCM connectors, wiring harnesses, junction blocks and nearby areas for damage, corrosion or water intrusion.
- Check relevant fuses and relays powering the PCM and CAN network.
- Measure power and ground at the PCM (key ON) — good ground and stable 12V supply required.
- Measure CAN_H and CAN_L with a multimeter and/or scope at the PCM connector and at other network nodes.
Signal parameters
- CAN bus idle voltages (approx): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (recessive).
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V).
- Termination resistance: ≈ 60 Ω measured between CAN_H and CAN_L (ignition OFF).
- Typical CAN data rates: commonly 500 kbps (powertrain) or 250 kbps on some networks — verify OEM spec.
- PCM message periodicity: many powertrain frames every 20–200 ms (varies by model and signal).
- If scanning: no response or timeouts from PCM, or bus-off / excessively high error counters.
Diagnostic algorithm
- Confirm the code: clear DTCs and attempt to re-create; verify U0100 returns and note any related codes.
- Check battery voltage and PCM power/ground circuits. Replace blown fuses and repair poor grounds before further testing.
- Scan all modules. Identify other U-codes indicating which part of the network is affected.
- Visually inspect PCM connector and nearby harness for corrosion, water damage, broken pins, or chafing. Repair or protect as needed.
- Measure CAN_H and CAN_L at PCM connector and at other nodes with ignition ON. Look for stuck dominant (one line held low/high) or missing differential.
- With ignition OFF, measure resistance between CAN_H and CAN_L across the network — expect ≈60 Ω. If infinite or very low, isolate sections to find open or short.
- Use a scope to verify proper differential signaling while cranking/running. Look for noise, missing frames, or bus-off conditions.
- Disconnect suspect aftermarket devices and modules one at a time to see if communication is restored.
- If wiring and connectors check good, check for available OEM reflash or programming updates for the PCM. Reprogram PCM per OEM procedure if indicated.
- If all else fails and wiring/terminals are verified, consider PCM replacement as last resort; follow OEM procedures for programming and initialization.
- After repair, clear codes and verify full network communication and proper operation during a road test or extended monitoring.
Likely causes
- Blown fuse or loose battery/PCM power/ground
- Damaged connector at PCM or a nearby splice (water intrusion or corrosion)
- Short to battery or ground on CAN_H or CAN_L from harness damage
- Faulty PCM (less common than wiring/connector issues)
- Aftermarket devices (alarms, chargers) interfering with CAN
- Missing/failed termination resistor or bus short causing bus-off
Fault status
Status
U0100 — Lost Communication with ECM/PCM: CAN bus or PCM communication fault.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
U0100
Generic
U — Network/User
Lost Communication With ECM/PCM A
Views:
UK: 64
EN: 114
RU: 135
AI status
Completed
Completed
100%
Causes
- Failed or intermittent PCM/ECM
- Open, shorted or high-resistance CAN bus wiring (CAN_H/CAN_L)
- Poor power or ground to the PCM (blown fuse, bad ground, corroded connector)
- Disconnected, corroded or damaged connector pins at the PCM or junctions
- Missing or incorrect termination (open or shorted 120Ω resistors)
- Software/firmware mismatch or corrupted PCM software
Symptoms
- No communication with PCM on an OBD-II scanner (scanner shows 'NO COMM' or times out)
- Multiple modules show communication-related DTCs
- Engine may not crank or start, or exhibits limp-home mode
- Malfunction Indicator Lamp (MIL) or other warning lights
- Intermittent faults or total loss of drivetrain functions
- Reduced or no data from PCM on live-data stream (RPM, engine load, sensors)
What to check
- Verify battery voltage and condition (12.4–12.8 V at rest). Check while cranking if needed.
- Scan all modules and note additional U-codes; record freeze-frame and freeze DTC times.
- Visually inspect PCM connectors, wiring harnesses, junction blocks and nearby areas for damage, corrosion or water intrusion.
- Check relevant fuses and relays powering the PCM and CAN network.
- Measure power and ground at the PCM (key ON) — good ground and stable 12V supply required.
- Measure CAN_H and CAN_L with a multimeter and/or scope at the PCM connector and at other network nodes.
Signal parameters
- CAN bus idle voltages (approx): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (recessive).
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V).
- Termination resistance: ≈ 60 Ω measured between CAN_H and CAN_L (ignition OFF).
- Typical CAN data rates: commonly 500 kbps (powertrain) or 250 kbps on some networks — verify OEM spec.
- PCM message periodicity: many powertrain frames every 20–200 ms (varies by model and signal).
- If scanning: no response or timeouts from PCM, or bus-off / excessively high error counters.
Diagnostic algorithm
- Confirm the code: clear DTCs and attempt to re-create; verify U0100 returns and note any related codes.
- Check battery voltage and PCM power/ground circuits. Replace blown fuses and repair poor grounds before further testing.
- Scan all modules. Identify other U-codes indicating which part of the network is affected.
- Visually inspect PCM connector and nearby harness for corrosion, water damage, broken pins, or chafing. Repair or protect as needed.
- Measure CAN_H and CAN_L at PCM connector and at other nodes with ignition ON. Look for stuck dominant (one line held low/high) or missing differential.
- With ignition OFF, measure resistance between CAN_H and CAN_L across the network — expect ≈60 Ω. If infinite or very low, isolate sections to find open or short.
- Use a scope to verify proper differential signaling while cranking/running. Look for noise, missing frames, or bus-off conditions.
- Disconnect suspect aftermarket devices and modules one at a time to see if communication is restored.
- If wiring and connectors check good, check for available OEM reflash or programming updates for the PCM. Reprogram PCM per OEM procedure if indicated.
- If all else fails and wiring/terminals are verified, consider PCM replacement as last resort; follow OEM procedures for programming and initialization.
- After repair, clear codes and verify full network communication and proper operation during a road test or extended monitoring.
Likely causes
- Blown fuse or loose battery/PCM power/ground
- Damaged connector at PCM or a nearby splice (water intrusion or corrosion)
- Short to battery or ground on CAN_H or CAN_L from harness damage
- Faulty PCM (less common than wiring/connector issues)
- Aftermarket devices (alarms, chargers) interfering with CAN
- Missing/failed termination resistor or bus short causing bus-off
Fault status
Status
U0100 — Lost Communication with ECM/PCM: CAN bus or PCM communication fault.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
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Code
U0100
HYUNDAI
U — Network/User
Lost Communication With ECM/PCM “A” | TCS Communication | ECU Communication Line Malfunction | Lost Communication With ECM/PCM ‘A’ (C-CAN) | Lost Communication with ECM/PCM (ECU TIME OUT) | Lost Communication With ECM/PCM ‘A’ | CAN TIME OUT
Views:
UK: 44
EN: 87
RU: 77
AI status
Completed
Completed
100%
Causes
- Failed or intermittent PCM/ECM
- Open, shorted or high-resistance CAN bus wiring (CAN_H/CAN_L)
- Poor power or ground to the PCM (blown fuse, bad ground, corroded connector)
- Disconnected, corroded or damaged connector pins at the PCM or junctions
- Missing or incorrect termination (open or shorted 120Ω resistors)
- Software/firmware mismatch or corrupted PCM software
Symptoms
- No communication with PCM on an OBD-II scanner (scanner shows 'NO COMM' or times out)
- Multiple modules show communication-related DTCs
- Engine may not crank or start, or exhibits limp-home mode
- Malfunction Indicator Lamp (MIL) or other warning lights
- Intermittent faults or total loss of drivetrain functions
- Reduced or no data from PCM on live-data stream (RPM, engine load, sensors)
What to check
- Verify battery voltage and condition (12.4–12.8 V at rest). Check while cranking if needed.
- Scan all modules and note additional U-codes; record freeze-frame and freeze DTC times.
- Visually inspect PCM connectors, wiring harnesses, junction blocks and nearby areas for damage, corrosion or water intrusion.
- Check relevant fuses and relays powering the PCM and CAN network.
- Measure power and ground at the PCM (key ON) — good ground and stable 12V supply required.
- Measure CAN_H and CAN_L with a multimeter and/or scope at the PCM connector and at other network nodes.
Signal parameters
- CAN bus idle voltages (approx): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (recessive).
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V).
- Termination resistance: ≈ 60 Ω measured between CAN_H and CAN_L (ignition OFF).
- Typical CAN data rates: commonly 500 kbps (powertrain) or 250 kbps on some networks — verify OEM spec.
- PCM message periodicity: many powertrain frames every 20–200 ms (varies by model and signal).
- If scanning: no response or timeouts from PCM, or bus-off / excessively high error counters.
Diagnostic algorithm
- Confirm the code: clear DTCs and attempt to re-create; verify U0100 returns and note any related codes.
- Check battery voltage and PCM power/ground circuits. Replace blown fuses and repair poor grounds before further testing.
- Scan all modules. Identify other U-codes indicating which part of the network is affected.
- Visually inspect PCM connector and nearby harness for corrosion, water damage, broken pins, or chafing. Repair or protect as needed.
- Measure CAN_H and CAN_L at PCM connector and at other nodes with ignition ON. Look for stuck dominant (one line held low/high) or missing differential.
- With ignition OFF, measure resistance between CAN_H and CAN_L across the network — expect ≈60 Ω. If infinite or very low, isolate sections to find open or short.
- Use a scope to verify proper differential signaling while cranking/running. Look for noise, missing frames, or bus-off conditions.
- Disconnect suspect aftermarket devices and modules one at a time to see if communication is restored.
- If wiring and connectors check good, check for available OEM reflash or programming updates for the PCM. Reprogram PCM per OEM procedure if indicated.
- If all else fails and wiring/terminals are verified, consider PCM replacement as last resort; follow OEM procedures for programming and initialization.
- After repair, clear codes and verify full network communication and proper operation during a road test or extended monitoring.
Likely causes
- Blown fuse or loose battery/PCM power/ground
- Damaged connector at PCM or a nearby splice (water intrusion or corrosion)
- Short to battery or ground on CAN_H or CAN_L from harness damage
- Faulty PCM (less common than wiring/connector issues)
- Aftermarket devices (alarms, chargers) interfering with CAN
- Missing/failed termination resistor or bus short causing bus-off
Fault status
Status
U0100 — Lost Communication with ECM/PCM: CAN bus or PCM communication fault.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
U0100
LAND ROVER
U — Network/User
Lost communication with the engine control module / module control of power train 'A'
Views:
UK: 25
EN: 72
RU: 64
AI status
Completed
Completed
100%
Causes
- Failed or intermittent PCM/ECM
- Open, shorted or high-resistance CAN bus wiring (CAN_H/CAN_L)
- Poor power or ground to the PCM (blown fuse, bad ground, corroded connector)
- Disconnected, corroded or damaged connector pins at the PCM or junctions
- Missing or incorrect termination (open or shorted 120Ω resistors)
- Software/firmware mismatch or corrupted PCM software
Symptoms
- No communication with PCM on an OBD-II scanner (scanner shows 'NO COMM' or times out)
- Multiple modules show communication-related DTCs
- Engine may not crank or start, or exhibits limp-home mode
- Malfunction Indicator Lamp (MIL) or other warning lights
- Intermittent faults or total loss of drivetrain functions
- Reduced or no data from PCM on live-data stream (RPM, engine load, sensors)
What to check
- Verify battery voltage and condition (12.4–12.8 V at rest). Check while cranking if needed.
- Scan all modules and note additional U-codes; record freeze-frame and freeze DTC times.
- Visually inspect PCM connectors, wiring harnesses, junction blocks and nearby areas for damage, corrosion or water intrusion.
- Check relevant fuses and relays powering the PCM and CAN network.
- Measure power and ground at the PCM (key ON) — good ground and stable 12V supply required.
- Measure CAN_H and CAN_L with a multimeter and/or scope at the PCM connector and at other network nodes.
Signal parameters
- CAN bus idle voltages (approx): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (recessive).
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V).
- Termination resistance: ≈ 60 Ω measured between CAN_H and CAN_L (ignition OFF).
- Typical CAN data rates: commonly 500 kbps (powertrain) or 250 kbps on some networks — verify OEM spec.
- PCM message periodicity: many powertrain frames every 20–200 ms (varies by model and signal).
- If scanning: no response or timeouts from PCM, or bus-off / excessively high error counters.
Diagnostic algorithm
- Confirm the code: clear DTCs and attempt to re-create; verify U0100 returns and note any related codes.
- Check battery voltage and PCM power/ground circuits. Replace blown fuses and repair poor grounds before further testing.
- Scan all modules. Identify other U-codes indicating which part of the network is affected.
- Visually inspect PCM connector and nearby harness for corrosion, water damage, broken pins, or chafing. Repair or protect as needed.
- Measure CAN_H and CAN_L at PCM connector and at other nodes with ignition ON. Look for stuck dominant (one line held low/high) or missing differential.
- With ignition OFF, measure resistance between CAN_H and CAN_L across the network — expect ≈60 Ω. If infinite or very low, isolate sections to find open or short.
- Use a scope to verify proper differential signaling while cranking/running. Look for noise, missing frames, or bus-off conditions.
- Disconnect suspect aftermarket devices and modules one at a time to see if communication is restored.
- If wiring and connectors check good, check for available OEM reflash or programming updates for the PCM. Reprogram PCM per OEM procedure if indicated.
- If all else fails and wiring/terminals are verified, consider PCM replacement as last resort; follow OEM procedures for programming and initialization.
- After repair, clear codes and verify full network communication and proper operation during a road test or extended monitoring.
Likely causes
- Blown fuse or loose battery/PCM power/ground
- Damaged connector at PCM or a nearby splice (water intrusion or corrosion)
- Short to battery or ground on CAN_H or CAN_L from harness damage
- Faulty PCM (less common than wiring/connector issues)
- Aftermarket devices (alarms, chargers) interfering with CAN
- Missing/failed termination resistor or bus short causing bus-off
Fault status
Status
U0100 — Lost Communication with ECM/PCM: CAN bus or PCM communication fault.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
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Code
U0100
MERCEDES-BENZ
U — Network/User
Lost Communication with ECM/PCM A
Views:
UK: 52
EN: 91
RU: 84
AI status
Completed
Completed
100%
Causes
- Failed or intermittent PCM/ECM
- Open, shorted or high-resistance CAN bus wiring (CAN_H/CAN_L)
- Poor power or ground to the PCM (blown fuse, bad ground, corroded connector)
- Disconnected, corroded or damaged connector pins at the PCM or junctions
- Missing or incorrect termination (open or shorted 120Ω resistors)
- Software/firmware mismatch or corrupted PCM software
Symptoms
- No communication with PCM on an OBD-II scanner (scanner shows 'NO COMM' or times out)
- Multiple modules show communication-related DTCs
- Engine may not crank or start, or exhibits limp-home mode
- Malfunction Indicator Lamp (MIL) or other warning lights
- Intermittent faults or total loss of drivetrain functions
- Reduced or no data from PCM on live-data stream (RPM, engine load, sensors)
What to check
- Verify battery voltage and condition (12.4–12.8 V at rest). Check while cranking if needed.
- Scan all modules and note additional U-codes; record freeze-frame and freeze DTC times.
- Visually inspect PCM connectors, wiring harnesses, junction blocks and nearby areas for damage, corrosion or water intrusion.
- Check relevant fuses and relays powering the PCM and CAN network.
- Measure power and ground at the PCM (key ON) — good ground and stable 12V supply required.
- Measure CAN_H and CAN_L with a multimeter and/or scope at the PCM connector and at other network nodes.
Signal parameters
- CAN bus idle voltages (approx): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (recessive).
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V).
- Termination resistance: ≈ 60 Ω measured between CAN_H and CAN_L (ignition OFF).
- Typical CAN data rates: commonly 500 kbps (powertrain) or 250 kbps on some networks — verify OEM spec.
- PCM message periodicity: many powertrain frames every 20–200 ms (varies by model and signal).
- If scanning: no response or timeouts from PCM, or bus-off / excessively high error counters.
Diagnostic algorithm
- Confirm the code: clear DTCs and attempt to re-create; verify U0100 returns and note any related codes.
- Check battery voltage and PCM power/ground circuits. Replace blown fuses and repair poor grounds before further testing.
- Scan all modules. Identify other U-codes indicating which part of the network is affected.
- Visually inspect PCM connector and nearby harness for corrosion, water damage, broken pins, or chafing. Repair or protect as needed.
- Measure CAN_H and CAN_L at PCM connector and at other nodes with ignition ON. Look for stuck dominant (one line held low/high) or missing differential.
- With ignition OFF, measure resistance between CAN_H and CAN_L across the network — expect ≈60 Ω. If infinite or very low, isolate sections to find open or short.
- Use a scope to verify proper differential signaling while cranking/running. Look for noise, missing frames, or bus-off conditions.
- Disconnect suspect aftermarket devices and modules one at a time to see if communication is restored.
- If wiring and connectors check good, check for available OEM reflash or programming updates for the PCM. Reprogram PCM per OEM procedure if indicated.
- If all else fails and wiring/terminals are verified, consider PCM replacement as last resort; follow OEM procedures for programming and initialization.
- After repair, clear codes and verify full network communication and proper operation during a road test or extended monitoring.
Likely causes
- Blown fuse or loose battery/PCM power/ground
- Damaged connector at PCM or a nearby splice (water intrusion or corrosion)
- Short to battery or ground on CAN_H or CAN_L from harness damage
- Faulty PCM (less common than wiring/connector issues)
- Aftermarket devices (alarms, chargers) interfering with CAN
- Missing/failed termination resistor or bus short causing bus-off
Fault status
Status
U0100 — Lost Communication with ECM/PCM: CAN bus or PCM communication fault.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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