U0004

High Speed CAN Communication Bus (+) Low

U0004 is a generic OBD-II network diagnostic trouble code: High Speed CAN Communication Bus (+) Low. 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
U0004
Group
Network
System
Network
Severity
—
Need U0004 disabled?
RaceTune permanently disables any OBD-II trouble code on supported ECUs — for motorsport, off-road, and export use.
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Detailed reference content for U0004 is being prepared. What you see above — the code's group, system, and the software disable option below — is accurate and complete; the long-form explainer, common causes, symptoms, and diagnostic steps will appear here once they have been reviewed.

Related network codes

Disabling U0004 in software

RaceTune can permanently disable U0004 — 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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