U0032: Vehicle Communication Bus A (+) High

What it means

The communication bus A high-side line (CAN-H or equivalent) is at a higher voltage than allowed. Likely short to power or a transceiver fault that pulls the line high.

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

Bus A's positive line, commonly CAN-High on a high-speed CAN network, works with the paired negative line to carry messages between modules. U0032 sets when the positive line rises above its allowed range, consistent with a short to power or a bus transceiver pulling the line high and disrupting communication.

Common causes

Most likely first.

1. Bus high line shorted to battery
2. Transceiver in one node failed
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 and save freeze-frame data, identifying which bus A nodes are offline and whether other high-voltage or communication codes appeared at the same time.
2. Inspect the bus A positive wire and connectors for damage, pin contact with a power feed, corrosion, or harness chafing.
3. Check battery and charging voltage and verify power and grounds at affected modules to rule out a broader electrical fault.
4. Measure the positive bus line under the manufacturer's specified conditions and check for a short to power against the manufacturer's specification.
5. If the harness passes, isolate bus A nodes and the gateway one at a time using the manufacturer's procedure to identify a transceiver or routing fault.

Common fixes

• Repair a bus A positive wire shorted to a power supply.
• Repair damaged wiring or corroded connectors affecting the positive line.
• Correct a verified power or ground fault at an affected module.
• Replace a failed transceiver or repair gateway routing only after circuit isolation confirms the cause.

Can I keep driving?

Because this fault can disrupt bus A and put affected systems into limp mode or shut them down, avoid driving if vehicle control is limited or unpredictable. Have the vehicle recovered if safety-critical systems are unavailable.