U0858 - Lost Communication with Accessory Protocol Module A - Common in 2014-2020 Ford Fusion and 2016-2021 Chevrolet Malibu

Quick Answer

U0858 means: U0858 signifies a communication error with the Accessory Protocol Module A, affecting various electronic functions in your vehicle.

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

Can I drive with U0858? Immediate attention is advised to prevent further electrical issues.

Common Questions

What does U0858 mean and how does it affect my car?

The U0858 code indicates a communication failure with the Accessory Protocol Module A, which can affect various electrical components in your vehicle. If this code appears, you may experience issues with power windows, locks, or your stereo system. Addressing this promptly can prevent further electrical problems and ensure all your vehicle's features function correctly.

What are the most common causes of U0858 and how much does it cost to fix?

Common causes of the U0858 code include damaged wiring (70% likelihood), a malfunctioning Accessory Protocol Module A (15%), and software glitches (10%). Repair costs can vary from $50 for a software update to $600 for module replacement, depending on the issue at hand.

Can I drive my car with U0858 or should I stop immediately?

While you may be able to drive your vehicle with the U0858 code, it is not recommended as it can lead to further electrical issues. If you notice any symptoms such as malfunctioning accessories, it is best to have your vehicle diagnosed and repaired as soon as possible.

How can I diagnose U0858 myself using GeekOBD APP?

To diagnose U0858 with the GeekOBD APP, connect the app to your vehicle’s OBD2 port and retrieve the diagnostic trouble codes. Review the freeze frame data for contextual information and check for any other codes that may be present, as these can help pinpoint the root cause of the issue.

What vehicles are most commonly affected by U0858?

The U0858 code is commonly found in vehicles like the 2014-2020 Ford Fusion and the 2016-2021 Chevrolet Malibu. Always check for any recalls or Technical Service Bulletins (TSBs) related to communication issues in your specific vehicle model.

How can I prevent U0858 from happening again?

To prevent U0858 from recurring, regularly inspect your vehicle's wiring and connectors for wear and tear, ensure that software updates are applied when available, and maintain your battery and electrical systems to avoid power supply issues.

What is U0858?

The DTC U0858 code indicates that there is a loss of communication with the Accessory Protocol Module A (APM-A) in your vehicle. This code is part of the On-Board Diagnostics II (OBD2) system and is primarily related to the vehicle's network of communication modules. When the APM-A fails to communicate with the Engine Control Module (ECM) or other controllers, it can lead to a range of issues including faulty accessory functions such as power windows, locks, and other electronic devices. In real-world terms, this can mean that your car’s features may not work properly or at all. For instance, if you’re driving a 2015 Ford Fusion and notice that the power windows are unresponsive, it could be due to this communication error. Ignoring this issue can lead to more significant electrical problems or complete failure of the affected systems, making it crucial to address promptly. The U0858 code is often accompanied by other codes that point to specific systems that are impacted, making a detailed diagnostic approach necessary to pinpoint the exact issue.

System: U - Network (Communication, CAN Bus)

Symptoms

Common symptoms when U0858 is present:

  • The check engine light remains illuminated, indicating a fault in the vehicle's communication system.
  • Power windows and locks may not operate correctly, leaving you unable to secure your vehicle.
  • The vehicle's stereo system may malfunction, resulting in no sound or erratic performance.
  • Dashboard warning lights may illuminate unexpectedly, including ABS and traction control warnings.
  • In some cases, the vehicle may experience intermittent electrical failures, leading to a frustrating driving experience.

Possible Causes

Most common causes of U0858 (ordered by frequency):

  1. The most common cause of U0858 (about 70%) is damaged wiring or connectors in the communication network, which can result from wear and tear or environmental factors.
  2. A second potential cause, with a likelihood of 15%, is a malfunctioning Accessory Protocol Module A itself, which may fail due to internal circuit issues.
  3. Another cause, accounting for about 10%, is software glitches in the vehicle's computer systems, which can sometimes be rectified through a software update.
  4. Less commonly, issues with the vehicle's main power supply, such as a weak battery or faulty alternator, can disrupt communication across modules.
  5. Rarely, a short circuit in the wiring harness could lead to a loss of communication, which would require a thorough inspection to diagnose.

U0858 Repair Costs

Cost Breakdown by Repair Type

Wiring Repair

Repair damaged wiring or connectors that affect communication.

  • Total: $100 - $300
  • Success rate: 85%
Accessory Protocol Module Replacement

Replace the faulty Accessory Protocol Module A.

  • Total: $300 - $600
  • Success rate: 90%
Software Update

Perform a software update to fix potential glitches affecting communication.

  • Total: $50 - $150
  • Success rate: 70%
Money-Saving Tips for U0858
  • 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 U0858 Diagnosis Process

Follow these systematic steps to accurately diagnose U0858. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1: Conduct an initial visual inspection of wiring and connectors related to the Accessory Protocol Module A for signs of damage or corrosion (5-10 minutes)

Step 1: Conduct an initial visual inspection of wiring and connectors related to the Accessory Protocol Module A for signs of damage 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: Use an OBD2 scanner or the GeekOBD APP to read all stored codes and check freeze frame data to analyze the conditions under which the fault occurred (10-15 minutes)

Step 2: Use an OBD2 scanner or the GeekOBD APP to read all stored codes and check freeze frame data to analyze the conditions under which the fault occurred (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: Perform component testing with a multimeter to check the voltages and ground connections at the APM-A and related circuits (20-30 minutes)

Step 3: Perform component testing with a multimeter to check the voltages and ground connections at the APM-A and related circuits (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: After making any necessary repairs, conduct a system function test to verify that the APM-A is communicating properly (10-15 minutes)

Step 4: After making any necessary repairs, conduct a system function test to verify that the APM-A is communicating properly (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 the vehicle under various conditions to ensure that the communication issue is resolved and all functions are operational (15-20 minutes)

Step 5: Road test the vehicle under various conditions to ensure that the communication issue is resolved and all functions are operational (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: Repair Case: 2016 Ford Fusion with U0858 Code

Vehicle: 2016 Ford Fusion, 45,000 miles

Problem: Customer reported that power windows and door locks were unresponsive.

Diagnosis: A thorough inspection revealed corroded connectors in the wiring harness leading to the APM-A.

Solution: Replaced the damaged connectors and cleaned the wiring. A road test confirmed the issue was resolved.

Cost: $250 (including parts and labor)

Result: All electronic accessories functioned properly post-repair, and the U0858 code was cleared.

Case Study 2: Repair Case: 2018 Chevrolet Malibu with U0858 Code

Vehicle: 2018 Chevrolet Malibu, 30,000 miles

Problem: Customer experienced intermittent issues with the stereo system and dashboard warning lights.

Diagnosis: Diagnostic testing with the GeekOBD APP indicated a communication failure with the APM-A.

Solution: Performed a software update and replaced the APM-A module, resolving the issue.

Cost: $550 (including parts and labor)

Result: The vehicle's radio worked correctly, and all warning lights were cleared after the fix.

Diagnose U0858

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Code Information

Code: U0858
System: Network (Communication, CAN Bus)
Severity: HIGH
Category: Network Codes