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.

U0078

Lost Communication with Telephone Module

Lowelectrical

Overview

The U0078 diagnostic trouble code indicates lost communication with telephone 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

Airbag warning light on
Various electrical accessories intermittently failing
Cruise control not engaging
Instrument cluster displays blank or flickering

Common Causes

Software glitch requiring module reprogramming
Failed control module (ECM, TCM, BCM, etc.)
Rodent damage to wiring harness
Low battery voltage or failing alternator

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

Subaru OutbackFord F-150Nissan AltimaChevrolet Silverado

Related Codes

U0040 U0001 U0195

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.