U0940 - Communication Error in Vehicle Control Module (Common in 2015-2018 Chevrolet Silverado)

Quick Answer

U0940 means: U0940 indicates a communication error between vehicle control modules, often linked to wiring issues or faulty modules.

Fix: Check and replace faulty components Cost: $100 - $300 Time: 90-180 minutes

Can I drive with U0940? Immediate attention is recommended to avoid further complications.

Common Questions

What does U0940 mean and how does it affect my car?

U0940 indicates a communication breakdown between your vehicle's control modules. This could lead to poor engine performance, erratic behavior of electronic systems, and decreased fuel efficiency. It's essential to address this code promptly to prevent further complications.

What are the most common causes of U0940 and how much does it cost to fix?

Common causes include damaged wiring (60% likelihood), faulty control modules, and corrosion at connectors. Repair costs can range from $100 for wiring repairs to $800 for a control module replacement, depending on the severity of the issue.

Can I drive my car with U0940 or should I stop immediately?

While you may be able to drive your vehicle, it's advisable to address the U0940 code quickly. Ignoring it could lead to more significant issues, including safety hazards if critical systems fail.

How can I diagnose U0940 myself using GeekOBD APP?

Using the GeekOBD APP, you can scan for codes, view freeze frame data, and monitor real-time vehicle performance. Look for any irregularities in module communication and follow the steps to test and diagnose the problem.

What vehicles are most commonly affected by U0940?

Vehicles often affected by U0940 include 2015-2018 Chevrolet Silverado, GMC Sierra, and other GM models. These vehicles may have known recalls or Technical Service Bulletins (TSBs) related to communication issues.

How can I prevent U0940 from happening again?

Regular maintenance, including inspecting wiring and connectors, applying dielectric grease to prevent corrosion, and keeping the vehicle's software updated, can help prevent U0940 from reoccurring.

What is U0940?

DTC U0940 is a diagnostic trouble code indicating a communication error between the vehicle control modules. This code is often seen in various GM vehicles, including models like the Chevrolet Silverado and GMC Sierra from the years 2015 to 2018. When this code appears, it means that one of the modules in the vehicle's network is not communicating properly with others. This could lead to issues with various systems, such as the engine control module (ECM), transmission control module (TCM), or any other module that relies on data sharing to function correctly. The implications of this code can range from minor inconvenience, such as dashboard warning lights, to severe problems, like affecting engine performance, transmission behavior, or even vehicle safety systems. If left untreated, the underlying issue could worsen, leading to more costly repairs and potential safety hazards on the road. Therefore, understanding the causes and symptoms of DTC U0940 is crucial for timely and effective resolution. Ignoring this code could lead to increased risk of electronic failures, impacting critical vehicle operations.

System: U - Network (Communication, CAN Bus)

Symptoms

Common symptoms when U0940 is present:

  • The check engine light stays on constantly, indicating a persistent issue that needs to be addressed.
  • The vehicle experiences intermittent power loss, particularly during acceleration or when engaging various functions.
  • Fuel economy has decreased by 10-15%, suggesting that the engine may not be operating optimally due to communication issues.
  • Dashboard warning lights for multiple systems may illuminate, causing confusion and concern for the driver.
  • The vehicle may exhibit erratic behavior in electronic systems, such as malfunctioning cruise control or inconsistent gauge readings.

Possible Causes

Most common causes of U0940 (ordered by frequency):

  1. The most common cause of U0940 is damaged wiring or poor connections, which account for approximately 60% of cases. This can occur due to wear and tear or exposure to harsh conditions.
  2. Another frequent issue is a faulty control module, which may fail to communicate due to internal malfunctions or corruption of firmware.
  3. Corrosion at connector points can also lead to communication failures, making it essential to regularly inspect and maintain electrical connections.
  4. Less common but serious causes include software bugs within the vehicle's control modules, requiring a software update or reprogramming.
  5. A rare cause could involve electrical shorts or issues within the vehicle's body control module, which can be complex and require specialized diagnostic tools.

U0940 Repair Costs

Cost Breakdown by Repair Type

Wiring Repair and Connector Cleaning

Repairing damaged wiring and cleaning corroded connectors to restore communication.

  • Total: $100 - $300
  • Success rate: 80%
Control Module Replacement

Replacing a faulty control module to restore functionality.

  • Total: $400 - $800
  • Success rate: 90%
Software Update

Updating software in the control module to fix communication errors.

  • Total: $50 - $150
  • Success rate: 75%
Money-Saving Tips for U0940
  • Start with the most common and least expensive repairs first
  • Use GeekOBD APP to confirm diagnosis before replacing expensive parts
  • Consider preventive maintenance to avoid future occurrences
  • Compare prices for OEM vs aftermarket parts based on your needs
  • Address the issue promptly to prevent more expensive secondary damage

Diagnostic Steps

Professional U0940 Diagnosis Process

Follow these systematic steps to accurately diagnose U0940. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion (5-10 minutes)

Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion (5-10 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 2: Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context (10-15 minutes)

Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 3: Step 3: Component testing - Use a multimeter or specific diagnostic tools to test suspected components and check for continuity (20-30 minutes)

Step 3: Component testing - Use a multimeter or specific diagnostic tools to test suspected components and check for continuity (20-30 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 4: Step 4: System function test - Verify proper operation after repairs and clear codes using the GeekOBD APP (10-15 minutes)

Step 4: System function test - Verify proper operation after repairs and clear codes using the GeekOBD APP (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 5: Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success and ensure all systems function correctly (15-20 minutes)

Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success and ensure all systems function correctly (15-20 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.

Important Notes

  • Always verify the repair with GeekOBD APP after completing diagnostic steps
  • Clear codes and test drive to ensure the problem is resolved
  • Address underlying causes to prevent code recurrence

Real Repair Case Studies

Case Study 1: 2017 Chevrolet Silverado - Communication Error Resolution

Vehicle: 2017 Chevrolet Silverado, 75,000 miles

Problem: Customer reported intermittent check engine light and erratic transmission behavior.

Diagnosis: Diagnostic scan revealed U0940 and further inspection showed corroded connectors under the hood.

Solution: Cleaned connectors and repaired damaged wiring, then cleared codes and tested vehicle.

Cost: $250 (including parts and labor)

Result: The check engine light remained off after the repair, and the transmission operated smoothly.

Case Study 2: 2016 GMC Sierra - Module Replacement

Vehicle: 2016 GMC Sierra, 50,000 miles

Problem: Customer experienced multiple warning lights and poor engine performance.

Diagnosis: Scanned for codes and found U0940 along with a faulty ECM.

Solution: Replaced the ECM and performed a software update to ensure proper communication.

Cost: $600 (including parts and labor)

Result: Post-repair, the vehicle showed no warning lights and performed optimally.

Diagnose U0940

Use GeekOBD APP for professional diagnosis!

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  • Professional-grade analysis
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Code Information

Code: U0940
System: Network (Communication, CAN Bus)
Severity: HIGH
Category: Network Codes