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Home / DTC / U3146 — Invalid CAN Bus Message Received

U3146 — Invalid CAN Bus Message Received

Detailed page for trouble code U3146.

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Code

U3146

Generic U — Network/User

Invalid CAN Bus Message Received

Brand: Generic
Type: U — Network/User
Views: UK: 2 EN: 4 RU: 3
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Page language: EN

Causes

  • Faulty module sending malformed CAN messages
  • Intermittent or permanent wiring damage (shorts, opens, high resistance)
  • Improper or missing CAN bus termination
  • Bus signal interference (electrical noise, aftermarket devices)
  • Failed CAN transceiver in a module
  • Incorrect module software/calibration or firmware bug

Symptoms

  • MIL/ABS/airbag or other warnings illuminate depending on affected module
  • Intermittent loss of function of one or more modules (locks, gauges, climate, etc.)
  • Stored additional U-codes or module-specific communication errors
  • Odd CAN bus behavior on scan tool (corrupted frames, unexpected IDs)
  • Vehicle may run normally between communication errors or exhibit intermittent faults

What to check

  • Use a full-function scan tool and read all stored U and module codes; note freeze frame and timestamps
  • Check for other related U-codes and identify which modules report the error
  • Visually inspect CAN wiring, connectors, and grounds for damage, corrosion or loose pins
  • Measure CAN_H and CAN_L idle voltages with key on (typical recessive both ≈2.5 V; dominant states show expected differential)
  • Measure DC resistance across CAN_H and CAN_L to check termination (≈60 Ω when measured at two terminating nodes combined)
  • Monitor real-time CAN traffic with a scan tool or CAN bus analyzer to identify malformed messages or unexpected IDs

Signal parameters

  • CAN_H and CAN_L idle voltage: ≈2.5 V each (recessive); dominant ~CAN_H 3.5 V / CAN_L 1.5 V (differential ≈2.0 V)
  • Bus baud rate: common values 125 kbps, 250 kbps, 500 kbps, or 1 Mbps — confirm vehicle-specific
  • Message ID (CAN identifier) and expected valid IDs for the network
  • DLC (data length code) — expected length 0–8 bytes (classic CAN) or length per FD specification
  • Frame format: standard (11-bit) or extended (29-bit) identifiers as used on vehicle
  • CRC/checksum field (if used in specific protocol layers) and valid value rules

Diagnostic algorithm

  1. Record all stored codes and freeze frame data from every module. Note which modules report U3146 and any time stamps.
  2. Reproduce the fault while monitoring the CAN bus with a capable scan tool or CAN analyzer. Capture traffic when U3146 sets to identify malformed frames (bad ID, wrong DLC, bad checksum, or garbage bits).
  3. Identify the source node by matching the message ID(s) or physical transmitter recorded in captures. If source not obvious, isolate segments of the bus (disconnect nodes one at a time while monitoring) to find when the invalid message disappears.
  4. Visually inspect and wiggle test wiring, connectors and ground points for the suspected node(s). Repair any damaged wiring or corroded connectors.
  5. Check termination: measure resistance across CAN_H and CAN_L at appropriate service points; verify correct termination resistors are present and not open/shorted.
  6. Measure CAN_H / CAN_L voltages and check for excessive noise or incorrect idle voltages. Use an oscilloscope to inspect waveform integrity (edges, ringing, noise).
  7. If an aftermarket device is present, remove it and retest. Also check for modules with intermittent power/ground causing corrupted frames.
  8. If wiring and termination are good, update or reflash module software per manufacturer service info. If invalid frames originate from a specific module, consider replacing or bench-testing the module/transceiver.
  9. After repairs, clear codes, recreate conditions that initially set the code and verify the fault does not return. Monitor bus for stability over road test and multiple ignition cycles.

Likely causes

  • Defective electronic control module transmitting corrupt frames
  • Damaged or corroded connector/terminal on CAN_H or CAN_L
  • Missing or incorrect termination resistor (not ~60 Ω across the bus at key points)
  • Aftermarket accessory connected to CAN bus injecting invalid messages
  • Intermittent short to battery or ground causing bit errors

Fault status

⚠️ Status
Module received CAN message with invalid format/content (unexpected ID, data length, checksum/CRC or timing) and flagged it as invalid; communication fault stored.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0 - 3.0 hours

Similar codes

U0073 U0100 U0121 U0155 U0416
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