What it means
A control module is not receiving expected messages from the HVAC Control Module. HVAC functions may be unavailable; the code alone does not identify why communication was lost.
How it works
The HVAC control module manages cabin heating, ventilation, and air-conditioning settings and exchanges information with other modules over the vehicle network. U0164 sets when a receiving module does not get expected messages from the HVAC control module in time; it does not establish whether the module, its power, CAN wiring, or gateway routing is at fault.
Common causes
Most likely first.
- HVAC module unpowered
- CAN wiring to HVAC module broken
- Gateway module routing CAN messages incorrectly
Symptoms
- HVAC controls or functions may be unavailable
- Other communication codes
How to diagnose it
- Scan all modules and review freeze-frame or event data for related communication codes or a low-voltage event.
- Check whether the HVAC controls respond and which heating, cooling, or airflow functions are affected.
- Inspect the HVAC module's connectors, power and ground wiring, and CAN wiring for loose contacts, corrosion, damage, or moisture.
- Test HVAC-module power and ground under load against the manufacturer's specification.
- Test CAN communication at the HVAC module and check gateway routing with the vehicle's wiring diagram and diagnostic procedures.
Common fixes
- Reconnect or clean a loose or corroded HVAC-module connector.
- Repair damaged CAN, power, or ground wiring to the HVAC module.
- Restore a failed power or ground supply to the module.
- Correct gateway routing or configuration if network tests identify it.
- Replace the HVAC control module only after its electrical supplies and network connection pass testing.
Can I keep driving?
You can usually drive if the HVAC fault is limited to comfort functions, but loss of defrosting can reduce visibility; do not drive with the windscreen obscured. If several vehicle systems are affected, seek diagnosis promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.