What it means
The reporting module has lost communication with the rear HVAC control module. It sets this code when expected messages from that module are not received for a specified time.
How it works
The rear HVAC control module manages rear-cabin climate settings and communicates with other modules over the vehicle network. U0165 sets when the reporting module misses expected messages from the rear HVAC module for a specified time; low battery voltage, a supply fault, CAN wiring, or the module itself can interrupt those messages.
Common causes
Most likely first.
- Rear HVAC module power or ground fault
- Damaged or corroded network wiring or connectors
- CAN bus short or open circuit
- Rear HVAC module failure
- Low battery voltage
Symptoms
- Rear climate controls do not respond
- Rear heating or cooling stops working
- Warning lights or messages
- Other communication codes
How to diagnose it
- Scan all modules and review freeze-frame data for low voltage and other communication codes that could point to a shared network or supply problem.
- Check whether the rear climate controls respond and whether rear heating or cooling is lost.
- Inspect the rear HVAC module's connectors, power and ground wiring, and CAN wiring for corrosion, damage, loose contacts, or moisture.
- Test rear-module power and ground under load against the manufacturer's specification, and check battery condition if low voltage is recorded.
- Test CAN wiring and communication at the rear HVAC module, then assess the module and gateway using vehicle-specific diagnostic information.
Common fixes
- Clean or secure a loose or corroded rear HVAC-module connector.
- Repair damaged wiring or connectors on the rear module's power, ground, or CAN circuits.
- Correct a weak battery or faulty supply connection if testing confirms low voltage.
- Repair a CAN open or short after locating it with circuit tests.
- Replace the rear HVAC module only after its power, ground, and network circuits test correctly.
Can I keep driving?
If only rear climate control is affected, driving is generally possible, though rear passengers may lose heating or cooling. Make sure the front windscreen can be kept clear; investigate promptly if warning messages or other electrical faults appear.
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.