U0005: High Speed CAN Communication Bus (+) High

What it means

A high signal fault has been detected on the positive line of the high-speed CAN communication bus. The affected functions depend on the vehicle network layout.

At a glance

• Usually lights the warning light of the system that lost communication
• The engine or gearbox may go into limp mode

How it works

The high-speed CAN bus uses CAN-High and CAN-Low wires to exchange messages among control modules. U0005 indicates CAN-High is being detected at an abnormally high signal level, which can result from a short to battery voltage or another source driving the line high.

Common causes

Most likely first.

1. CAN-High shorted to battery voltage
2. Chafed harness against power wire
3. Gateway module routing CAN messages incorrectly

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Scan all modules for communication faults and determine which modules are affected, using the network layout to identify their shared CAN branch.
2. Inspect the CAN-High wire and nearby harness for chafing against a power wire, pinched insulation, or damage around recent repairs.
3. Check connectors for displaced pins, corrosion, or evidence of unintended contact between CAN-High and a power terminal.
4. Use the manufacturer’s network procedure to measure the CAN-High signal and check for a short to voltage with the bus safely isolated.
5. If no wiring short is found, isolate network branches and modules as directed by service information to locate a transceiver or gateway fault.

Common fixes

• Repair CAN-High wiring shorted to a power wire or battery supply.
• Replace or repair a connector with damaged terminals that bridge CAN-High to voltage.
• Secure the harness away from chafing or pinching points.
• Repair or replace a confirmed faulty network module or gateway after wiring checks pass.

Can I keep driving?

A CAN-High line held high can interrupt communication and cause limp mode or loss of vehicle functions. Avoid driving if essential systems are affected or the vehicle behaves unpredictably; even if it runs normally, keep travel limited because more modules may lose communication.