U1924

Code

Generic U — Network/User

Invalid CAN Bus Message from Control Module

Brand: Generic

Type: U — Network/User

Views: UK: 17 EN: 26 RU: 29

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Page language: EN

Malfunction indicator lamp (MIL) or network warning lamp illuminated
Loss or intermittent operation of functions controlled by the offending module
Multiple U-codes or communication-related codes stored in different modules
Scanner shows module present but with erratic or invalid data frames
Features that depend on the message may not work (e.g., instrument cluster, ADAS, HVAC)

Read and record all stored codes and freeze frame data from all modules
Check for related U-codes that indicate bus-off or bus faults
Visually inspect CAN wiring, connectors, and module grounds for damage or corrosion
Verify battery state-of-charge and charging system stability
Measure CAN bus termination resistance (approx. 60 ohms across CAN H-L on a two-node terminated bus)
Use a scan tool to monitor live CAN messages and verify the offending message ID and timing

High-speed CAN typical voltages: recessive ~2.5 V on CANH and CANL, dominant CANH ≈ 3.5 V and CANL ≈ 1.5 V (differential ≈ 2 V)
Typical termination: two 120 Ω resistors in parallel = ~60 Ω across CAN H-L
Common bus speeds: 125 kbps, 250 kbps, 500 kbps (vehicle-specific; mismatched baud rates cause invalid frames)
CAN 2.0 message length: DLC 0–8 bytes; CAN FD allows longer payloads (may be incompatible if misconfigured)

Record all active and pending codes from every control module. Note freeze frame data and timestamp information.
Clear codes and attempt to reproduce. If U1924 returns, note frequency and conditions (key on, driving, accessory on).
Inspect harnesses, connectors and module mounting for damage, water intrusion, or corrosion. Repair any physical faults.
Verify battery and charging system voltages and grounds to eliminate power-related noise.
Measure termination resistance across CAN H-L with ignition off. Expect ~60 Ω for a properly terminated high-speed bus.
Use a scan tool to watch CAN traffic. Identify the message ID reported as invalid and which module transmits it (if possible).
Capture waveforms on CAN H and CAN L with an oscilloscope while reproducing the fault. Look for missing recessive levels, reflections, distorted edges, or noise.
If a specific module is suspected, disconnect that module (follow manufacturer procedures) and re-check the bus; note that disconnecting can set additional codes—proceed cautiously.
Reflash or update module software/calibration if a configuration mismatch is suspected and OEM updates are available.
Replace faulty wiring, connectors, transceiver or the control module only after confirming the module is the source of malformed messages. Verify repair by clearing codes and performing a functional test/road test.