Can a weak battery cause communication codes?

Yes, low battery voltage is one of the most common causes of U-codes. Control modules need stable voltage to communicate. Always check battery and alternator before replacing expensive modules.

Is it safe to drive with communication fault codes?

It depends on which module lost communication. Loss of ECM or ABS communication can affect engine performance and braking safety. Loss of entertainment or comfort modules is less critical. Have any U-code diagnosed promptly.

U0065

Lost Communication with Auxiliary HVAC Module

Lowelectrical

Overview

The U0065 diagnostic trouble code indicates lost communication with auxiliary hvac module. This means one or more control modules on the vehicle's communication network are unable to exchange data properly. Network communication faults can affect multiple vehicle systems simultaneously and may cause various warning lights, reduced functionality, or driveability issues depending on which modules are affected.

Symptoms

Check engine light on
Vehicle may not start or stall unexpectedly
Infotainment system unresponsive
Loss of power steering assist

Common Causes

Failed control module (ECM, TCM, BCM, etc.)
Poor ground connection at module
Water damage to module or wiring harness
Software glitch requiring module reprogramming

Diagnosis Steps

1Connect an OBD-II scanner and read all stored trouble codes across all modules
2Check for multiple U-codes which indicate a bus-level problem vs single module failure
3Inspect battery voltage and charging system (12.4V+ engine off, 13.5-14.5V running)
4Inspect the CAN bus wiring for damage, chafing, or exposed conductors
5Check the affected module connector for corrosion, bent pins, or water intrusion
6Verify module power and ground circuits with a multimeter

Estimated Repair Cost

$100 — $1,500

Cost varies by vehicle, location, and repair shop. Includes parts and labor.

Commonly Affected Vehicles

Mercedes-Benz C-ClassToyota RAV4Honda CR-VDodge Ram 1500

Related Codes

U0046 U0150 U0003

More Electrical Codes

B0001Driver Frontal Airbag Deployment Loop Circuit Open

Critical

B0002Driver Frontal Airbag Deployment Loop Circuit Short to Ground

Critical

B0003Driver Frontal Airbag Deployment Loop Circuit Short to Battery

Critical

B0004Driver Frontal Airbag Deployment Loop Resistance Too High

Critical

B0005Driver Frontal Airbag Deployment Loop Resistance Too Low

Critical

B0006Passenger Frontal Airbag Deployment Loop Circuit Open

Critical

Frequently Asked Questions

U-codes are network communication codes that indicate a control module has lost communication with another module. This can be caused by wiring problems, a failed module, low battery voltage, or CAN bus issues. Multiple U-codes usually point to a bus-level problem.