U0046

Vehicle Communication Bus C

U0046 is a generic OBD-II network diagnostic trouble code: Vehicle Communication Bus C. It is logged by the engine control unit when the network monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
U0046
Group
Network
System
Network
Severity
Warning (MIL on)
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What U0046 means

DTC U0046 is a network communication fault indicating that the ECM or another module has lost communication with the Body Control Module (BCM) over the vehicle CAN bus. The BCM is a central hub that manages numerous body electrical functions including lighting, power windows, door locks, and security, and it shares data with the ECM and other modules via the bus.

Loss of BCM communication can stem from a fault in the BCM itself, a wiring fault on the CAN bus segment shared with the BCM, a missing or improper bus termination resistance, or a power or ground supply fault to the BCM that prevents it from transmitting on the network. In some cases, a shorted module elsewhere on the same bus segment can drag down bus voltage and disrupt all communication on that network segment.

When the ECM cannot receive BCM data, it may default certain body-related inputs to a safe state, potentially affecting security interlock functions, auxiliary lighting control, or other body-ECM shared operations. Additional module-specific codes will typically accompany U0046 on other modules that also lost BCM communication.

Common causes

Most-frequently reported root causes when U0046 is logged.

  • 1
    BCM power supply or ground fault preventing normal bus communication.
  • 2
    Damaged or shorted CAN bus wiring on the segment connected to the BCM.
  • 3
    Failed BCM unable to transmit on the network.
  • 4
    Incorrect or missing CAN bus termination resistance.
  • 5
    Another module on the same bus segment shorted and dragging bus lines low.
  • 6
    Corroded or damaged BCM harness connector.
  • 7
    Blown BCM fuse or relay causing complete module power loss.

Symptoms drivers notice

MIL or multiple warning lights illuminated.
Multiple module communication faults stored across several control units.
Body electrical functions such as lighting, locks, and windows may be inoperative or erratic.
Security or immobilizer faults may appear.
Loss of communication between ECM and body-related inputs.

How to diagnose U0046

A typical diagnostic flow when this code is present.

  1. 1
    Scan all modules for DTCs to establish which modules report loss of BCM communication.
  2. 2
    Check BCM fuses and relay circuits for proper power and ground supply.
  3. 3
    Measure CAN bus voltage at the BCM connector with ignition on to confirm bus activity.
  4. 4
    Inspect the BCM harness connector for corrosion, backed-out pins, or damage.
  5. 5
    Measure CAN bus termination resistance (expected approximately 60 ohms between CAN-H and CAN-L with all modules unpowered).
  6. 6
    Disconnect modules one at a time on the suspect bus segment to isolate a shorted module dragging the bus down.
  7. 7
    Replace or reprogram the BCM only after confirming bus integrity and power supply are correct.

Related network codes

Frequently asked questions

Will U0046 always set a MIL?

Not always on every vehicle. Some manufacturers store U0046 as a historical code without illuminating the MIL if the fault is intermittent.

Can a dead battery cause U0046?

Yes. Severely low battery voltage can prevent modules from communicating, generating spurious U-codes. Always ensure the battery is fully charged before diagnosing network codes.

Is U0046 the same on all vehicle makes?

The code number is standardized by SAE J2012, but the specific BCM functions and which network segment it occupies vary by manufacturer.

Should I replace the BCM if I get U0046?

Not before confirming the bus wiring, power supply, and connector are sound. A wiring fault or shorted module is more often the cause than a failed BCM.

Disabling U0046 in software

RaceTune can permanently disable U0046 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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