What Does U0165 Mean?
The powertrain control module (PCM) or body control module (BCM) has lost communication with the rear HVAC control module over the vehicle's communication network. This indicates a breakdown in data exchange between climate control systems.
Common Causes
35%
Faulty rear HVAC control module with internal circuit failure
30%
Damaged or corroded wiring harness between modules
20%
CAN bus network fault or termination resistor failure
10%
Blown fuse or loss of power supply to rear HVAC module
5%
Software corruption or module configuration error
Diagnostic Steps
1
Step 1: Check all fuses related to rear HVAC system and verify power and ground at the rear HVAC control module connector
2
Step 2: Inspect wiring harness and connectors between BCM and rear HVAC module for damage, corrosion, or loose connections
3
Step 3: Use scan tool to monitor CAN bus communication and check for voltage on CAN High/Low circuits (should be approximately 2.5V at rest)
4
Step 4: Substitute or reflash rear HVAC control module if power, ground, and communication circuits test good
5
Step 5: Check for technical service bulletins (TSBs) related to rear HVAC communication issues for the specific vehicle
Estimated Repair Cost
$150 - $800
Parts + labor, varies by vehicle and location
The powertrain control module (PCM) or body control module (BCM) has lost communication with the rear HVAC control module over the vehicle's communication network. This indicates a breakdown in data exchange between climate control systems.
The most common cause of U0165 (Lost Communication With Rear HVAC Control Module) is: Faulty rear HVAC control module with internal circuit failure
Typical repair costs for U0165 range from $150 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
No direct safety impact. Vehicle remains safe to drive but rear climate control functions may be inoperative.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0165 to identify the root cause.
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Quick Info
Category
Network
System
Climate Control / HVAC
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
