P1851 Code: Complete DIY Repair Guide

The P1851 trouble code is a diagnostic trouble code (DTC) that indicates an issue within the vehicle’s transmission system, specifically related to the brake band apply solenoid performance or the transmission transfer case contact plate. This code is part of the OBD-II system, which helps in diagnosing problems with a vehicle’s powertrain. Understanding the P1851 code is crucial for vehicle owners and DIY mechanics, as it can affect vehicle performance and safety.

Symptoms of P1851 Code

When the P1851 code is triggered, drivers may experience various symptoms that can indicate underlying issues. Common symptoms include:

• Check Engine Light: The most obvious sign is the illumination of the check engine light on the dashboard.
• Transmission Issues: Drivers may notice slipping, harsh shifting, or delayed engagement when shifting gears.
• Reduced Power: The vehicle may exhibit a lack of power during acceleration.
• Unusual Sounds: Grinding or whining noises from the transmission can also occur.
• Poor Fuel Economy: A decrease in fuel efficiency may be observed due to improper transmission operation.

Technical Explanation of P1851 Code

The P1851 code relates to specific components within the vehicle’s transmission system. Here’s a breakdown of its technical aspects:

• Transmission Transfer Case Contact Plate: This component is responsible for managing signals related to gear selection and transfer case operation. An open circuit in this area can lead to incorrect readings and poor performance.
• Brake Band Apply Solenoid: This solenoid controls the application of brake bands within the transmission, which are essential for gear engagement. Performance issues here can lead to poor shifting and increased wear on transmission components.
• Data Bus Communication: Modern vehicles rely on a network of electronic modules that communicate via a data bus. If there’s a missing message from critical components such as the brake control module, it can trigger diagnostic codes like P1851.

Step-by-Step Diagnosis of P1851 Code

Diagnosing the P1851 code involves several steps to pinpoint the exact cause of the issue:

1. Scan for Codes: Use an OBD-II scanner to confirm that the P1851 code is present along with any other related codes.
2. Visual Inspection:

• Check wiring and connectors associated with the transmission and brake control systems for damage or corrosion.
• Inspect fluid levels and quality in the transmission system.

1. Test Components:

• Use a multimeter to check resistance and continuity in wiring related to the solenoid and transfer case contact plate.
• Test the brake band apply solenoid for proper operation.

1. Check Data Bus Communication:

• Verify that all modules are communicating correctly using a scan tool capable of reading live data.
• Look for any fault codes in related modules, such as ABS or engine control units.

1. Fluid Condition Check:

• Assess the condition of transmission fluid; it should be clean and at proper levels.
• If fluid appears dirty or burnt, consider a fluid change.

Solution Methods for P1851 Code

Once diagnosed, there are several potential solutions depending on the identified issue:

• Repair Wiring Issues: If damaged wiring or connectors are found, repair or replace them as necessary.
• Replace Faulty Components:
• If the brake band apply solenoid is defective, it will need replacement.
• Replace any malfunctioning sensors or modules that are contributing to communication errors.
• Fluid Change: If transmission fluid is low or contaminated, perform a complete fluid change and check for leaks.
• Reprogram Modules: In some cases, reprogramming or resetting modules may resolve communication issues on the data bus.

Cost Estimates for Repairs

The cost to repair issues related to a P1851 code can vary widely based on several factors:

• Diagnostic Fees: Expect to pay between $100-$150 for a professional diagnostic service if you choose not to diagnose it yourself.
• Parts Costs:
• Brake band apply solenoids typically range from $50 to $200.
• Transmission fluid changes can cost between $100 and $300 depending on labor costs and fluid type used.
• Labor Costs: Labor rates vary but generally range from $75 to $150 per hour.

Overall, total repair costs can range from $200 to over $1000 depending on parts needed and labor involved.

Warnings and Recommendations

• Always consult your vehicle’s service manual for specific diagnostics related to your make and model before proceeding with repairs.
• If you are not comfortable performing these diagnostics or repairs yourself, seek professional assistance to avoid further damage.
• Regular maintenance of your vehicle’s transmission fluid can prevent many issues associated with DTCs like P1851.

Closing Paragraph

Understanding and addressing the P1851 trouble code is crucial for maintaining your vehicle’s performance and safety. By following this guide, DIY mechanics can effectively diagnose and rectify issues related to this code. Whether it’s checking wiring connections, replacing faulty components, or ensuring proper fluid levels, taking proactive steps can save time and money while keeping your vehicle running smoothly.

Frequently Asked Questions About P1851

• What does error code P1851 mean?
  P1851 indicates an issue with either the brake band apply solenoid performance or an open circuit in the transmission transfer case contact plate.
• Can I drive my car with a P1851 code?
  While you might be able to drive temporarily, it’s advisable to address this issue promptly as it can lead to more severe transmission problems.
• How do I clear a P1851 code?
  You can clear the code using an OBD-II scanner after addressing any underlying issues; however, simply clearing it without fixing problems will likely result in it returning.
• What are common symptoms of a P1851 code?
  Common symptoms include harsh shifting, slipping gears, illuminated check engine light, and reduced power during acceleration.
• Is it safe to ignore a P1851 code?
  No, ignoring this code can lead to further damage to your vehicle’s transmission system.
• What tools do I need to diagnose a P1851 code?
  A basic OBD-II scanner will help read codes; additional tools may include multimeters for electrical testing.
• Can low transmission fluid cause a P1851 code?
  Yes, low or contaminated transmission fluid can lead to performance issues triggering this trouble code.
• When should I seek professional help for a P1851 code?
  If you’re unable to diagnose or fix the problem after following basic troubleshooting steps, it’s best to consult a professional mechanic.