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All codes/U0004

U0004

High Speed CAN Communication Bus Low

High severity

The CAN-High signal stays below its valid voltage window. Common cause is a short to ground on the CAN-H wire or a transceiver that pulls the line down. The bus stops working until the offending node is isolated.

The CAN-High signal stays below its valid voltage window. Common cause is a short to ground on the CAN-H wire or a transceiver that pulls the line down. The bus stops working until the offending node is isolated.

Common causes

  • CAN-High shorted to ground

    One of the most commonly reported causes for this code — check this first.

    high

    Typical part cost: $90-770

  • Internal transceiver failure on a node

    A plausible cause — test and verify before replacing parts.

    medium

    Typical part cost: $90-770

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First things to check

  1. 1Confirm the code with a scan tool and check for additional related codes.
  2. 2Inspect the relevant sensors, wiring, and connectors for damage or corrosion.

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Tools you may need

Already have a compatible scanner? Use it. If not, a Bluetooth OBD2 adapter can help you confirm engine codes and check supported live sensor data before replacing parts.

Illustration of a Bluetooth OBD2 adapter, not a product photo

Basic checks

Veepeak OBDCheck BLE

A Bluetooth LE adapter for reading standard engine codes and supported live data.

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Illustration of a Bluetooth OBD2 adapter, not a product photo

Regular diagnostics

vgate iCar Pro BLE 4.0

A Bluetooth LE adapter with an automatic sleep feature for routine code and sensor checks.

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Illustration of a Bluetooth OBD2 adapter, not a product photo

Another option

OBDLink CX

A Bluetooth LE adapter to consider when comparing supported vehicles and diagnostic apps.

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Illustrations shown, not product photos. Check vehicle, phone and app compatibility before buying. These adapters do not guarantee access to ABS, airbags or manufacturer-specific systems. Clearing a code does not repair the fault and can reset emissions readiness monitors.

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Related codes

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Frequently asked questions

What does U0004 mean?

U0004 means "High Speed CAN Communication Bus Low". It is a generic OBD-II code that points to a fault in the network / communication.

What are the most common causes of U0004?

can-high shorted to ground; internal transceiver failure on a node; gateway module routing can messages incorrectly — these are the most commonly reported causes. Verify with a proper diagnosis before replacing parts, or use the Wrenchify app for a vehicle-specific diagnosis.

Can I keep driving with this code?

This code can put the vehicle into limp or reduced-power mode. Avoid extended driving and have the vehicle diagnosed promptly. Use the Wrenchify app for a full diagnosis specific to your vehicle.

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