P1855 Code: Complete DIY Repair Guide

The P1855 trouble code is a manufacturer-specific diagnostic trouble code (DTC) that indicates an issue related to the transmission transfer case contact plate ‘C’ open circuit. This code is part of the OBD-II system, which monitors various components of a vehicle’s engine and transmission systems. When this code appears, it typically signals that there is a malfunction in the communication between the transmission control module (TCM) and the transfer case, which can lead to performance issues in a vehicle’s drivetrain.

Symptoms of P1855 Code

When the P1855 code is triggered, vehicle owners may experience several symptoms, including:

• Check Engine Light: The most common indicator is the illumination of the check engine light on the dashboard.
• Transmission Issues: Drivers may notice erratic shifting, slipping, or difficulty in engaging gears.
• Reduced Power: There might be a noticeable decrease in engine power during acceleration.
• Unusual Noises: Grinding or clunking noises may occur from the transmission area.
• Increased Fuel Consumption: The vehicle may experience lower fuel efficiency due to transmission inefficiencies.

Technical Explanation

The P1855 code specifically relates to the transfer case’s contact plate ‘C,’ which is responsible for relaying information between the TCM and other components. When this circuit experiences an open condition, it disrupts communication and can lead to improper functioning of the vehicle’s drivetrain.

This issue can stem from various causes such as faulty wiring, a defective TCM, or issues with the transfer case motor itself. Additionally, software mismatches within the TCM can prevent it from properly interpreting signals from the contact plate.

Step-by-Step Diagnosis

To diagnose a P1855 trouble code effectively, follow these steps:

1. Scan for Codes: Use an OBD-II scanner to confirm the presence of the P1855 code and check for any additional codes that may provide further insight.
2. Visual Inspection: Inspect wiring and connectors associated with the transfer case contact plate for signs of damage, corrosion, or loose connections.
3. Check Power and Ground: Ensure that there is proper power and ground at the contact plate connector using a multimeter.
4. Test Continuity: Use a multimeter to test for continuity in the wiring between the TCM and the contact plate. Look for any breaks or shorts in the circuit.
5. Examine TCM Functionality: If all wiring checks out, consider testing or replacing the TCM if it is suspected to be malfunctioning.
6. Inspect Transfer Case Motor: Check if the transfer case motor operates correctly. If it does not engage properly, it may need replacement.
7. Reprogram/Update Software: If there are software mismatches, reprogramming or updating the TCM may resolve communication issues.
8. Test Drive: After repairs are made, clear any codes and take the vehicle for a test drive to ensure that the problem has been resolved.

Solution Methods

Here are some potential solutions for addressing a P1855 trouble code:

• Repair Wiring Issues: If damaged wiring or connectors are found during inspection, repair or replace them as necessary to restore proper communication.
• Replace Faulty Components:
• If testing reveals a defective TCM or transfer case motor, replace these components.
• Reprogram TCM: If software mismatches are identified, reprogramming or updating the TCM may be required to ensure compatibility with other systems.
• Clear Codes and Test Drive: After making repairs, clear any stored codes and perform a test drive to confirm that the issue has been resolved.

Cost Estimates

The cost of repairing a P1855 trouble code can vary significantly based on several factors:

• Wiring Repairs: Simple wire repairs can range from $50 to $200 depending on labor costs.
• TCM Replacement: A new transmission control module can cost between $300 and $800 plus labor.
• Transfer Case Motor Replacement: This can range from $200 to $600 depending on parts and labor costs.
• Software Reprogramming: Typically costs between $100 and $300 at a dealership or specialized shop.

Warnings and Recommendations

• Always consult your vehicle’s service manual for specific diagnostic procedures related to your make and model.
• If you are not comfortable performing these diagnostics or repairs yourself, consider seeking professional assistance from an ASE-certified technician.
• Ignoring a P1855 code could lead to more severe transmission problems over time, so it’s advisable to address it promptly.

Closing Paragraph

The P1855 trouble code indicates significant issues within your vehicle’s transmission system that require immediate attention. By understanding its meaning, symptoms, causes, and solutions outlined in this guide, DIY mechanics can effectively diagnose and resolve this issue. Always prioritize safety when working on your vehicle and do not hesitate to seek professional help if needed.

Frequently Asked Questions About P1855

• What does P1855 mean?
  P1855 indicates an open circuit in the transmission transfer case contact plate ‘C’, affecting communication between components.
• How serious is a P1855 code?
  A P1855 code can lead to transmission malfunctions if not addressed promptly; it’s important to diagnose it as soon as possible.
• Can I drive with a P1855 code?
  You can drive with this code temporarily if there are no immediate symptoms; however, it’s recommended to fix it soon.
• What tools do I need to diagnose P1855?
  A basic OBD-II scanner, multimeter for electrical tests, and basic hand tools for inspections are necessary.
• How much does it cost to fix a P1855?
  The cost varies widely but can range from $50 for minor repairs up to $800 for component replacements.
• Can I reset my check engine light after fixing P1855?
  Yes, after repairs are made, you can reset your check engine light using an OBD-II scanner.
• What vehicles commonly have P1855 codes?
  This code appears across various makes but is particularly noted in vehicles with advanced transmission systems like Audi and Volkswagen.
• Is professional help necessary for P1855?
  If you’re unsure about diagnosing or repairing electrical issues yourself, professional assistance is highly recommended.