AutoDiag

U0073

Control Module Communication Bus "A" Off

High· Fix promptlyProfessionalNetworkGeneric, all makes

What it means

A module has detected that the communication bus has shut down completely.

Is it safe to drive?

Drive with caution; several systems may not work.

Symptoms

  • Many warning lights
  • Possible no-start

Probable causes

Most likely first

  1. 1Network wiring short
  2. 2Failed module on the bus
  3. 3Low battery voltage

How to diagnose it

Work through these in order before buying parts

  1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
  2. 2Check the battery and charging voltage. Low voltage is the most common cause of communication codes.
  3. 3Scan all modules: if one module is missing from the list, focus on its power, ground and connectors.
  4. 4Check the fuses that feed the module that is not communicating.
  5. 5With the battery disconnected, measure resistance between CAN High and CAN Low at the diagnostic port; about 60 Ω is normal.
  6. 6Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

  • Repair the wiring
  • Replace the faulty module

This information is general guidance for all makes. Exact causes, specifications and procedures vary by vehicle, so confirm with your service manual or a qualified mechanic before replacing parts.