Code
U1120
MITSUBISHI
U — Network/User
Engine(CAN message)
Views:
UK: 10
EN: 16
RU: 15
AI status
Completed
Completed
100%
Causes
- Faulty or intermittent connection at the Engine Control Module (ECM/ECU) connector
- Broken, shorted, or high-resistance CAN bus wiring (CAN High / CAN Low)
- Corroded or poorly seated connectors on CAN network or ECM power/ground
- Blown fuse or loss of power/ground to the ECM
- Faulty ECM or other network module that transmits the engine message
- Incorrect CAN termination (missing/bad resistors) or bus voltage out of spec
Symptoms
- Malfunction Indicator Lamp (MIL) or warning lights illuminated
- Engine-related data unavailable on other modules (no RPM, load, etc.)
- Reduced engine performance or limp-home mode in some cases
- Unable to start or intermittent cranking issues if ECM not communicating
- Loss of features that rely on engine data (instrument cluster, ABS, HVAC status)
- Stored communication faults and multiple related U-codes
What to check
- Read all stored DTCs and freeze frame with a scan tool; note related U-codes and history
- Confirm whether the Engine module appears on the CAN network (live data/Module present list)
- Visually inspect ECM connectors, wiring harness, and grounding points for damage or corrosion
- Check vehicle battery voltage and charging system health
- Verify fuses and power/ground circuits to the ECM are present and within spec
- Measure CAN bus resistance between CAN_H and CAN_L (typical ≈60 ohms with ignition off)
Signal parameters
- Typical idle (recessive) voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both hover near midpoint)
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V)
- Termination resistance: approx. 60 ohms across CAN_H and CAN_L (two 120 Ω in parallel)
- Common powertrain CAN baud rate: often 500 kbps (verify model-specific rate in service manual)
- Expected: consistent periodic broadcast from ECM containing engine RPM, coolant temp, load, etc. (absent or intermittent in U1120)
Diagnostic algorithm
- Use a scan tool to confirm U1120 and record all related U- and P-codes and freeze frame data.
- Check vehicle battery voltage (12.4–12.9 V with engine off) and charging system while running; low voltage can cause comms errors.
- Inspect ECM connector, wiring harness, and nearby grounds for damage, corrosion, or loose terminals; repair as needed.
- Verify fuses and power/ground circuits to the ECM are intact and supplying correct voltages.
- With ignition on, measure CAN_H and CAN_L at a convenient connector or ECM pin: verify recessive and dominant voltages and check termination resistance (≈60 Ω).
- Use a scan tool or CAN bus monitor to look for the ECM’s messages on the bus. If absent, isolate whether the ECM or another module is the source by disconnecting non-essential nodes (follow OEM isolation procedure).
- If intermittent, perform wiggle tests on harnesses and connectors while monitoring the bus for changes; check for chafing or intermittent short/opens.
- Check for aftermarket accessories tied into the bus; disconnect and retest.
- If ECM power/ground and wiring are good but no engine messages appear, consider reprogramming or replacement of the ECM/gateway per factory procedures.
- After repairs, clear codes and verify proper communication and that codes do not return under various operating conditions.
Likely causes
- Open, short, or high resistance in CAN wiring between ECM and gateway
- Loss of ECM power or ground (fuse, connector, battery)
- Corroded/damaged connector at ECM or gateway
- Failed ECM or gateway module
- Aftermarket accessory driving fault onto CAN bus
Fault status
Status
Control module detected missing, invalid, or intermittent Engine CAN message (communication fault).
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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Code
U1120
Other
U — Network/User
SCP (J1850) Invalid or Missing Data for Primary Id
Views:
UK: 19
EN: 25
RU: 25
AI status
Completed
Completed
100%
Causes
- Faulty or intermittent connection at the Engine Control Module (ECM/ECU) connector
- Broken, shorted, or high-resistance CAN bus wiring (CAN High / CAN Low)
- Corroded or poorly seated connectors on CAN network or ECM power/ground
- Blown fuse or loss of power/ground to the ECM
- Faulty ECM or other network module that transmits the engine message
- Incorrect CAN termination (missing/bad resistors) or bus voltage out of spec
Symptoms
- Malfunction Indicator Lamp (MIL) or warning lights illuminated
- Engine-related data unavailable on other modules (no RPM, load, etc.)
- Reduced engine performance or limp-home mode in some cases
- Unable to start or intermittent cranking issues if ECM not communicating
- Loss of features that rely on engine data (instrument cluster, ABS, HVAC status)
- Stored communication faults and multiple related U-codes
What to check
- Read all stored DTCs and freeze frame with a scan tool; note related U-codes and history
- Confirm whether the Engine module appears on the CAN network (live data/Module present list)
- Visually inspect ECM connectors, wiring harness, and grounding points for damage or corrosion
- Check vehicle battery voltage and charging system health
- Verify fuses and power/ground circuits to the ECM are present and within spec
- Measure CAN bus resistance between CAN_H and CAN_L (typical ≈60 ohms with ignition off)
Signal parameters
- Typical idle (recessive) voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both hover near midpoint)
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V)
- Termination resistance: approx. 60 ohms across CAN_H and CAN_L (two 120 Ω in parallel)
- Common powertrain CAN baud rate: often 500 kbps (verify model-specific rate in service manual)
- Expected: consistent periodic broadcast from ECM containing engine RPM, coolant temp, load, etc. (absent or intermittent in U1120)
Diagnostic algorithm
- Use a scan tool to confirm U1120 and record all related U- and P-codes and freeze frame data.
- Check vehicle battery voltage (12.4–12.9 V with engine off) and charging system while running; low voltage can cause comms errors.
- Inspect ECM connector, wiring harness, and nearby grounds for damage, corrosion, or loose terminals; repair as needed.
- Verify fuses and power/ground circuits to the ECM are intact and supplying correct voltages.
- With ignition on, measure CAN_H and CAN_L at a convenient connector or ECM pin: verify recessive and dominant voltages and check termination resistance (≈60 Ω).
- Use a scan tool or CAN bus monitor to look for the ECM’s messages on the bus. If absent, isolate whether the ECM or another module is the source by disconnecting non-essential nodes (follow OEM isolation procedure).
- If intermittent, perform wiggle tests on harnesses and connectors while monitoring the bus for changes; check for chafing or intermittent short/opens.
- Check for aftermarket accessories tied into the bus; disconnect and retest.
- If ECM power/ground and wiring are good but no engine messages appear, consider reprogramming or replacement of the ECM/gateway per factory procedures.
- After repairs, clear codes and verify proper communication and that codes do not return under various operating conditions.
Likely causes
- Open, short, or high resistance in CAN wiring between ECM and gateway
- Loss of ECM power or ground (fuse, connector, battery)
- Corroded/damaged connector at ECM or gateway
- Failed ECM or gateway module
- Aftermarket accessory driving fault onto CAN bus
Fault status
Status
Control module detected missing, invalid, or intermittent Engine CAN message (communication fault).
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
Similar codes
Your experience will help others
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👍 Like
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