What Is the U0079 Code?
The U0079 diagnostic trouble code (DTC) indicates that the vehicle has detected a communication failure on Control Module Communication Bus G. This network allows multiple electronic control modules to exchange data continuously. When Bus G becomes unavailable or stops communicating, one or more control modules may be unable to exchange information, causing the control module to store the U0079 diagnostic trouble code.
Communication network failures are commonly caused by wiring damage, poor electrical connections, module power supply problems, network shorts, or an internal fault within one of the connected control modules. Because several modules share the same communication network, diagnosing the root cause requires checking the entire communication system rather than replacing a single control module immediately.
U0079 may appear together with additional communication-related DTCs such as lost communication codes. Those related codes usually identify the affected module and should always be diagnosed before replacing components.
Can I Drive With U0079?
Driving may still be possible if only a non-critical control module has lost communication. However, if important systems such as ABS, Electronic Stability Control, Steering, Transmission, or Engine Control are affected, vehicle performance and safety may be reduced. The communication network should be diagnosed as soon as possible to prevent additional module failures.
Common Symptoms
| Symptom | Description |
|---|---|
| Check Engine Light | MIL or warning lamps may illuminate. |
| Communication DTCs | Multiple U-codes may be stored. |
| Electronic System Malfunctions | ABS, ESC, or other systems may become unavailable. |
| Intermittent Module Operation | Some modules may temporarily stop responding. |
Common Causes
| Cause | Description |
|---|---|
| Open CAN Bus Circuit | Broken communication wiring interrupts data transfer. |
| Short to Ground or Power | Electrical shorts disable communication on Bus G. |
| Loose or Corroded Connectors | Poor terminal contact causes intermittent communication. |
| Failed Control Module | A defective module may stop network communication. |
| Low Battery Voltage | Insufficient system voltage may interrupt module operation. |
| Poor Ground Connection | High ground resistance affects communication stability. |
Typical Communication Network Diagram
Diagnosis Procedure
Diagnosis should begin with a complete vehicle scan to identify every stored communication DTC. Related U-codes often indicate which control module has stopped communicating on Bus G.
Step 1: Scan All Control Modules
Use a professional scan tool capable of communicating with every module installed on the vehicle and record all communication-related diagnostic trouble codes.
Step 2: Verify Battery Voltage
Confirm proper battery voltage and charging system operation before performing network diagnostics.
Step 3: Inspect CAN Bus Wiring
Inspect CAN-H and CAN-L wiring, connectors, splice joints, and module terminals for corrosion, damaged insulation, open circuits, or short circuits.
Step 4: Measure Network Resistance
With the ignition switched OFF, measure CAN Bus resistance. A healthy communication network normally measures approximately 60 Ω. Readings significantly above or below this value indicate network wiring or termination problems.
Estimated Repair Cost
| Repair | Estimated Cost |
|---|---|
| Professional Diagnosis | $80–200 |
| CAN Wiring Repair | $50–350 |
| Connector Repair | $50–150 |
| Control Module Replacement | $300–1,500+ |
Typical Live Data
The U0079 diagnostic trouble code does not have dedicated Live Data values. Instead, technicians diagnose the fault by monitoring CAN Bus communication parameters using professional diagnostic scan tools. These values help identify communication interruptions, offline modules, and network performance problems.
Advanced Scan Tool Live Data Access
Professional diagnostic equipment provides access to CAN Bus information through the Gateway Module, Network Management menu, Communication Status screen, or individual control modules connected to Bus G.
Useful parameters include CAN High Voltage, CAN Low Voltage, Bus Load, Module Communication Status, Gateway Status, Network Error Counter, Communication Timeout Counter, Module Online Status, and Bus Utilization.
| Parameter | Typical Value | Fault Indication |
|---|---|---|
| CAN High (CAN-H) | Approximately 2.5–3.5 V | Fixed Voltage / No Activity |
| CAN Low (CAN-L) | Approximately 2.5–1.5 V | Fixed Voltage / No Activity |
| Module Status | Online | Offline / Timeout |
| CAN Bus Resistance | Approximately 60 Ω | 0 Ω / 120 Ω / Open Circuit |
Oscilloscope Waveform Analysis
A dual-channel oscilloscope is one of the most effective tools for diagnosing U0079. Monitoring CAN-H and CAN-L simultaneously allows technicians to identify electrical noise, waveform distortion, voltage imbalance, intermittent communication failures, and complete network shutdown.
Normal CAN Bus Waveform
Distorted CAN Bus Waveform
No Communication Waveform
Common Repair Mistakes
One of the most common mistakes when diagnosing U0079 is replacing a control module before inspecting the CAN Bus wiring. In many cases, communication failures are caused by damaged wiring, poor electrical connections, corroded terminals, or low system voltage rather than a failed electronic module.
Another common mistake is diagnosing only the module that stored U0079. Since several control modules share the same communication network, technicians should perform a complete network scan and investigate all related U-codes before replacing any components.
Always save Freeze Frame Data and every stored DTC before clearing diagnostic memory, as related communication codes often identify the actual source of the network failure.
Recommended Diagnostic Tools
Professional diagnosis of U0079 requires a full-system diagnostic scanner capable of communicating with every installed control module, a digital multimeter, a dual-channel oscilloscope, manufacturer wiring diagrams, and official service information.
Advanced scan tools allow technicians to monitor CAN Bus status, module communication, Gateway information, Live Data, network topology, communication error counters, and module online status, making communication faults much easier to locate.
When electrical faults are suspected, oscilloscope testing of CAN-H and CAN-L signals provides the most reliable method for identifying waveform distortion, voltage imbalance, electrical noise, intermittent communication failures, and complete Bus G shutdown.
Frequently Asked Questions (FAQ)
What does U0079 mean?
U0079 indicates that Control Module Communication Bus G has stopped communicating. One or more electronic control modules can no longer exchange information across the communication network.
Can I continue driving with U0079?
Possibly. If the affected module controls critical vehicle functions such as ABS, steering, transmission, or engine management, vehicle safety and performance may be reduced. Diagnosis is recommended as soon as possible.
What is the most common cause of U0079?
Damaged CAN Bus wiring, poor connectors, low battery voltage, faulty module power or ground circuits, and defective control modules are the most common causes of this communication fault.
Should related U-codes be diagnosed first?
Yes. Additional communication DTCs usually identify which control module has stopped responding and greatly simplify the diagnostic process.
Related Sections
Continue exploring professional communication network diagnostics:
U Code
Live Data
Acronyms
ADAS
Sensors
Conclusion
The U0079 diagnostic trouble code indicates that Control Module Communication Bus G is no longer operating correctly, preventing one or more electronic control modules from exchanging data across the vehicle network. Communication failures are commonly caused by wiring faults, poor electrical connections, low system voltage, or a defective control module.
A systematic diagnostic approach—including a complete network scan, battery and ground verification, CAN Bus resistance testing, Live Data analysis, and oscilloscope waveform inspection—helps identify the root cause while preventing unnecessary replacement of expensive electronic modules.
OBD Spark provides professional OBD-II diagnostic information, CAN Bus troubleshooting guides, Live Data references, oscilloscope waveform analysis, and repair procedures for technicians and vehicle owners.
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