U0076

Reserved by Document

U0076 is a generic OBD-II network diagnostic trouble code: Reserved by Document. 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
U0076
Group
Network
System
Network
Severity
Warning (MIL on, possible limp mode)
Need U0076 disabled?
RaceTune permanently disables any OBD-II trouble code on supported ECUs — for motorsport, off-road, and export use.
→

What U0076 means

U0076 indicates that the ECM or a module monitoring Bus A has detected that the communication bus is in a Bus Off state. In CAN bus architecture, a node enters Bus Off when it detects a critical level of transmission errors, causing it to disconnect from the network to prevent further disruption.

Bus Off events are typically triggered by persistent electrical faults such as a short circuit between the CAN High and CAN Low lines, a missing termination resistor, or a faulty module that is continuously flooding the bus with errors. The affected bus segment can carry multiple critical control modules, so a Bus Off condition may cause widespread communication losses and multiple concurrent U-codes.

Diagnosis requires identifying which physical segment corresponds to Bus A on the vehicle in question, then systematically checking the bus wiring, termination resistance, and each module on that segment. A CAN bus analyser or oscilloscope is strongly recommended to observe bus activity before assuming a module has failed.

Common causes

Most-frequently reported root causes when U0076 is logged.

  • 1
    Short circuit between CAN High and CAN Low wires on Bus A.
  • 2
    Missing or incorrect termination resistor at one or both ends of the bus.
  • 3
    A module on Bus A continuously transmitting error frames and driving Bus Off.
  • 4
    Open circuit in the CAN High or CAN Low wire interrupting network continuity.
  • 5
    Corroded or damaged connector causing intermittent bus signal integrity issues.
  • 6
    Water intrusion into a module or connector on the Bus A segment.
  • 7
    Failed internal CAN transceiver in one of the modules on the bus.

Symptoms drivers notice

MIL and/or multiple warning lights illuminated simultaneously.
Multiple U-codes stored alongside U0076.
Loss of communication with one or more control modules.
Certain vehicle systems (transmission, ABS, stability control) may be inoperative.
Engine may enter limp mode if critical powertrain modules are affected.

How to diagnose U0076

A typical diagnostic flow when this code is present.

  1. 1
    Record all stored DTCs across all modules to map which modules are affected.
  2. 2
    Identify the physical wiring and modules belonging to Bus A on this specific vehicle.
  3. 3
    Measure the bus termination resistance between CAN High and CAN Low (expect approximately 60 ohms with both terminators in circuit).
  4. 4
    Inspect bus wiring harness for shorts, opens, or damage, especially in high-wear areas.
  5. 5
    Use a scan tool or oscilloscope to check for bus activity and error frames.
  6. 6
    Disconnect modules one at a time to identify a module generating continuous error frames.
  7. 7
    Repair wiring faults or replace the faulty module as identified, then verify bus communication is restored.

Related network codes

Frequently asked questions

Why do I have so many U-codes at the same time?

U0076 Bus Off causes the entire Bus A segment to go silent, so every module that normally communicates on that bus will log a lost-communication code simultaneously.

Can a bad module cause U0076 even if the wiring is fine?

Yes. A module with a failing CAN transceiver can flood the bus with error frames until the bus enters the Bus Off state.

What is the correct termination resistance for a CAN bus?

Most CAN buses use 120-ohm termination resistors at each end, giving approximately 60 ohms measured across the bus with both terminators in circuit.

Is U0076 specific to one bus or the entire network?

It is specific to the segment designated Bus A. Other bus segments (B, C, etc.) may still function normally if the fault is isolated to Bus A.

Disabling U0076 in software

RaceTune can permanently disable U0076 — 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.

Got U0076 in your scan?

Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.

Upload your file