U0804 - Understanding Communication Error in CAN Bus (Common in 2015-2018 Ford F-150, Chevrolet Silverado)

Quick Answer

U0804 means: U0804 indicates a communication problem within the vehicle's CAN bus, affecting module interactions.

Fix: Check and replace faulty components Cost: $150 - $400 Time: 90-180 minutes

Can I drive with U0804? Address promptly to avoid further electronic issues.

Common Questions

What does U0804 mean and how does it affect my car?

The U0804 code signifies a communication error between modules in your vehicle's CAN bus system. If unresolved, it can lead to performance issues like stalling, erratic engine behavior, or even render your vehicle inoperable. It's crucial to address this code promptly to maintain your vehicle's functionality.

What are the most common causes of U0804 and how much does it cost to fix?

Common causes include damaged wiring and faulty modules, with repair costs ranging from $150 to $1200 depending on the specific issue. Regular maintenance can help mitigate these risks.

Can I drive my car with U0804 or should I stop immediately?

While you might be able to drive short distances after seeing the U0804 code, it’s not advisable. Ignoring the issue can lead to more severe electronic system failures, so it's best to address it as soon as possible.

How can I diagnose U0804 myself using GeekOBD APP?

Using the GeekOBD APP, you can scan for diagnostic trouble codes. Focus on retrieving U0804 and any related codes. Analyze the freeze frame data to understand when the error occurred and check the specific modules involved.

What vehicles are most commonly affected by U0804?

The U0804 code is frequently seen in models like the 2015-2018 Ford F-150 and Chevrolet Silverado. Always check for any recalls or Technical Service Bulletins (TSBs) related to communication issues in these vehicles.

How can I prevent U0804 from happening again?

To prevent U0804, maintain your vehicle's electrical system by regularly checking wiring and connectors for wear. Consider software updates during routine maintenance to ensure modules are functioning correctly.

What is U0804?

The diagnostic trouble code (DTC) U0804 indicates a communication issue within the Controller Area Network (CAN) bus of your vehicle. This code generally signals that a module within the vehicle’s network is not communicating properly with other modules. The CAN bus is a critical system that allows various electronic components of your vehicle, such as the engine control unit (ECU), transmission control module, and other systems, to communicate with one another. When U0804 is triggered, it means there’s a problem with the data exchange between these modules, potentially leading to a range of performance issues. For vehicle owners, this could manifest as engine performance problems, warning lights on the dashboard, or even a complete inability to start the vehicle. Ignoring this code can lead to more significant issues down the road, including damage to the electronic control systems, increased repair costs, and potential safety risks. Diagnosing and fixing U0804 early is crucial to ensuring the reliable operation of your vehicle. Regular maintenance checks and addressing any electronic issues promptly can help avoid the complications associated with this trouble code.

System: U - Network (Communication, CAN Bus)

Symptoms

Common symptoms when U0804 is present:

  • The check engine light remains illuminated, indicating a persistent issue that requires attention.
  • Engine performance may suffer; for example, you might notice hesitation or stalling during acceleration.
  • You could experience a significant drop in fuel efficiency, often around 10-15%, affecting your vehicle's overall performance.
  • The vehicle may exhibit erratic behavior, such as the dashboard lights flickering or gauges reading inaccurately.
  • In some cases, you might face starting issues where the engine cranks but does not start, preventing you from driving.

Possible Causes

Most common causes of U0804 (ordered by frequency):

  1. The most common cause of U0804 is a faulty CAN bus connector or damaged wiring, accounting for approximately 40% of cases. If the wiring harness is frayed or the connections are loose, data may not transmit correctly.
  2. Another frequent cause is a malfunctioning module, such as the ECM or TCM. If one of these control units fails, it can disrupt communications within the CAN bus, leading to this error code.
  3. A third possible cause involves software issues or glitches in the vehicle's control modules. Keeping the software updated can help prevent such issues.
  4. Less commonly, water intrusion into electrical connectors can cause U0804. This situation usually arises from poor sealing or damage to the vehicle's body.
  5. A rare but serious cause could be a short circuit in the CAN bus system, potentially leading to complete failure of communication between critical modules.

U0804 Repair Costs

Cost Breakdown by Repair Type

Wiring Repair/Replacement

Repairing or replacing damaged wiring and connectors within the CAN bus.

  • Total: $150 - $400
  • Success rate: 85%
Module Replacement

Replacing a faulty control module such as the ECM or TCM.

  • Total: $500 - $1200
  • Success rate: 90%
Software Update

Updating the software of the affected modules to resolve communication errors.

  • Total: $100 - $200
  • Success rate: 75%
Money-Saving Tips for U0804
  • 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 U0804 Diagnosis Process

Follow these systematic steps to accurately diagnose U0804. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1: Initial visual inspection - Check for any obvious signs of wear, such as damaged wiring, loose connections, or corrosion

Step 1: Initial visual inspection - Check for any obvious signs of wear, such as damaged wiring, loose connections, or corrosion. This can take about 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 - Use the GeekOBD APP to retrieve all diagnostic trouble codes and freeze frame data to understand the context of the fault

Step 2: OBD2 scan with GeekOBD APP - Use the GeekOBD APP to retrieve all diagnostic trouble codes and freeze frame data to understand the context of the fault. This step usually takes around 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 - Utilize a multimeter or specific diagnostic tools to test the suspected components identified from the scan

Step 3: Component testing - Utilize a multimeter or specific diagnostic tools to test the suspected components identified from the scan. Expect this to take 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 - After any repairs, verify the operation of the system to ensure everything is functioning correctly and clear any codes with the GeekOBD APP

Step 4: System function test - After any repairs, verify the operation of the system to ensure everything is functioning correctly and clear any codes with the GeekOBD APP. Allow about 10-15 minutes for this step.

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 - Finally, drive the vehicle under various conditions to confirm the success of the repairs, which can take 15-20 minutes

Step 5: Road test verification - Finally, drive the vehicle under various conditions to confirm the success of the repairs, which can take 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: Resolving U0804 in a 2016 Ford F-150

Vehicle: 2016 Ford F-150, 75,000 miles

Problem: Customer reported persistent check engine light and poor acceleration.

Diagnosis: After scanning with GeekOBD APP, U0804 was identified along with other communication errors. A visual inspection revealed damaged wiring in the CAN bus.

Solution: Replaced the damaged wiring and secured all connectors. Updated the software in the ECM.

Cost: $350 (parts: $150 for wiring, labor: $200)

Result: The check engine light was cleared, and the vehicle's performance returned to normal.

Case Study 2: Fixing U0804 in a 2017 Chevrolet Silverado

Vehicle: 2017 Chevrolet Silverado, 50,000 miles

Problem: Owner experienced stalling and erratic dashboard signals.

Diagnosis: DTC U0804 was flagged during the diagnostic scan. Further investigation indicated a malfunctioning ECM.

Solution: Replaced the ECM, performed a system function test, and cleared all codes.

Cost: $950 (parts: $750 for the ECM, labor: $200)

Result: Vehicle operated smoothly post-repair with no further issues.

Diagnose U0804

Use GeekOBD APP for professional diagnosis!

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  • Step-by-step repair guidance
  • Professional-grade analysis
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Code Information

Code: U0804
System: Network (Communication, CAN Bus)
Severity: HIGH
Category: Network Codes