CAN network

U0164 — Lost Communication with HVAC Control Module B

Severity: low Safe to drive

What U0164 means

U0164 means a module on the CAN bus stopped answering the secondary HVAC control module (module B). This is typically the rear climate unit or the second zone on a dual-zone system. Modules normally exchange messages constantly, and when messages stop, the control unit sets the code and disables the related functions.

Symptoms

  • Rear climate control does not work
  • Temperature settings between zones do not sync
  • Buttons or controls on the second unit are unresponsive
  • Additional warning lights may come on
  • Functions of the affected module are unavailable

Possible causes

  1. Faulty rear or secondary HVAC module
  2. Open, shorted or chafed CAN wiring, including in the console area
  3. Corroded connectors or terminals
  4. Power supply or ground fault at the module
  5. Low system voltage or a weak battery
  6. Another faulty module loading the bus

How to diagnose

  1. Check battery voltage and terminal condition
  2. Scan all modules and note which ones do not communicate
  3. Clear the codes and see whether U0164 returns
  4. Inspect the HVAC module connectors and harness, especially under the console
  5. Check power and ground at the module connector
  6. Measure CAN bus resistance and voltages at the diagnostic connector
  7. If needed, unplug suspect modules one at a time, only following the manufacturer's documented procedure

Common fixes

  • Repair damaged CAN wires and replace damaged connectors
  • Clean corroded terminals and contacts
  • Fix the power or ground fault at the module
  • Replace the faulty HVAC module and program it if required
  • Charge or replace the battery

Questions and answers

Can I drive with a U0164 code?

Usually yes, because the code concerns climate control and not the engine or brakes. If other communication codes are present, have the car checked soon.

What does U0164 mean?

It means communication with HVAC control module B, typically the rear or second zone, was lost. The module is not answering on the CAN bus because of a module, wiring or power problem.

Can a weak battery cause U0164?

Yes, low voltage can disrupt communication between modules. Check the battery and terminals first, then move on to the wiring and the module.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.