U0DA8

Lost Communication With Electric Motor Control Module

U0DA8 is a generic OBD-II network diagnostic trouble code: Lost Communication With Electric Motor Control Module. 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
U0DA8
Group
Network
System
Network
Severity
Critical (limp mode / no-start)
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What U0DA8 means

U0DA8 is set when the vehicle network loses communication with the electric motor control module, the ECU responsible for managing the traction motor operation on an electric or hybrid vehicle. This module translates driver torque requests into motor current commands and reports back motor speed, torque, and fault status to the vehicle management system. Without this communication link, the vehicle cannot safely or accurately control motor torque output.

Loss of communication with the motor control module is a critical event because traction motor output cannot be managed without it. Most platforms respond by cutting motor drive and entering a fail-safe mode, which may leave the vehicle unable to move under electric power. On hybrid vehicles with a combustion engine, limited propulsion through the combustion side may remain available depending on the architecture.

High-voltage safety precautions are mandatory for all diagnosis of this code. The 12V supply to the motor control module should be the first check, followed by CAN bus integrity. Co-set codes from the inverter, battery management module, and propulsion controller will help determine whether the communication failure is isolated to the motor control module or is part of a broader network event.

Common causes

Most-frequently reported root causes when U0DA8 is logged.

  • 1
    Loss of 12V control power or ground to the electric motor control module.
  • 2
    Open or shorted CAN bus wiring serving the motor control module.
  • 3
    Failed electric motor control module no longer communicating on the network.
  • 4
    Corroded or damaged connector at the motor control module.
  • 5
    Overtemperature protection event causing the module to shut down communications.
  • 6
    High-voltage interlock loop (HVIL) fault causing the module to disable.
  • 7
    CAN bus wiring damage caused by heat exposure near the motor or inverter assembly.

Symptoms drivers notice

Loss of electric drive power; vehicle may not move or enters severe limp mode.
Electric motor or powertrain warning lamp illuminated.
Scan tool cannot communicate with the electric motor control module.
Other high-voltage drivetrain communication codes co-set alongside U0DA8.
On hybrid vehicles, combustion engine may continue to run but EV drive is unavailable.

How to diagnose U0DA8

A typical diagnostic flow when this code is present.

  1. 1
    Apply full high-voltage safety precautions per the manufacturer procedure before starting diagnosis.
  2. 2
    Use an enhanced or manufacturer-specific scan tool to retrieve all module DTCs and document co-set network codes.
  3. 3
    Verify 12V supply voltage and ground at the electric motor control module connector.
  4. 4
    Inspect the module connector and wiring harness for damage, heat exposure, or corrosion.
  5. 5
    Measure CAN bus differential voltage at the motor control module connector with the ignition on.
  6. 6
    Check the high-voltage interlock loop if applicable, as HVIL faults can trigger module shutdown.
  7. 7
    If power, ground, and CAN signal are confirmed but no module response is present, the module has likely failed; follow manufacturer procedures for high-voltage module replacement.

Related network codes

Frequently asked questions

Is U0DA8 different from a motor inverter fault?

Yes. The motor control module is the ECU that commands the motor, while the inverter is the power electronics that execute those commands. U0DA8 is a network communication fault with the control module, not a power electronics fault.

Can regenerative braking still work with U0DA8?

Regenerative braking is commanded through the same motor control module. If that module is not communicating, regenerative braking is typically disabled and the vehicle will rely on friction brakes only.

Could a software crash in the motor module cause U0DA8?

Yes. A software exception or watchdog reset in the motor control module can cause it to drop off the network temporarily or permanently. Check for software update bulletins before replacing the module.

Is this code ever triggered by a loose CAN bus connector?

Yes. Vibration-induced connector movement near the motor assembly is a known cause of intermittent U0DA8. Inspect all CAN bus connectors in the drivetrain area carefully for proper seating and terminal condition.

Disabling U0DA8 in software

RaceTune can permanently disable U0DA8 — 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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