P1851 Code: Here’s How to Solve It Fast

The P1851 trouble code is a diagnostic trouble code (DTC) that indicates a malfunction within the transmission system, specifically related to the brake band apply solenoid performance or contact plate issues in the transfer case. This code can trigger the check engine light and may lead to erratic transmission behavior if not addressed promptly. Understanding the causes, symptoms, and solutions for the P1851 code is essential for vehicle owners and DIY mechanics looking to maintain their vehicles effectively.

P1851 Code Meaning	P1851 Code Common Causes
Brake Band Apply Solenoid Performance Issue	Dirty or low transmission fluid
Transmission Transfer Case Contact Plate B Open Circuit	Damaged wiring or connectors
Erratic Transmission Behavior	Failed brake band apply solenoid
Delayed Shifts or Slipping Gears	Clogged hydraulic passages
Check Engine Light Activation	Valve body problems

Table of Contents

Symptoms of P1851 Code

When the P1851 code is triggered, several symptoms may manifest, indicating potential issues within the transmission system. Recognizing these symptoms early can help prevent further damage:

Check Engine Light: The most common indicator that something is wrong.
Delayed Shifts: Difficulty in shifting gears or noticeable delays during gear changes.
Slipping Gears: The vehicle may unexpectedly slip out of gear while driving.
Erratic Transmission Behavior: Unpredictable shifting patterns or harsh engagement of gears.
Burning Smell: A burning odor may indicate overheating transmission fluid.
Transmission Overheating: The transmission may run hotter than normal due to internal issues.

Technical Explanations

The P1851 code is associated with two primary issues:

Brake Band Apply Solenoid Performance: This solenoid is responsible for applying pressure to the brake bands in the transmission, allowing smooth gear shifts. If it fails, it can lead to slipping or harsh shifts.
Contact Plate B Open Circuit: In vehicles equipped with a transfer case, this refers to an open circuit in the contact plate that can disrupt communication between various components, leading to erratic behavior.

Understanding these components and their functions is crucial for effective diagnosis and repair.

Step-by-Step Diagnosis

Diagnosing a P1851 code requires a systematic approach:

Scan for Codes: Use an OBD-II scanner to confirm the presence of the P1851 code and check for any additional codes that may offer more context.
Inspect Transmission Fluid: Check the condition and level of the transmission fluid. Look for signs of contamination or burning.
Examine Wiring and Connectors: Inspect all wiring and connectors related to the brake band apply solenoid and transfer case for damage or corrosion.
Test Brake Band Apply Solenoid: Use a multimeter to test the solenoid’s resistance and functionality.
Check Hydraulic Passages: If necessary, perform a hydraulic pressure test to ensure there are no clogs affecting performance.
Consult Service Manual: Refer to your vehicle’s service manual for specific diagnostic procedures related to your make and model.

Solution Methods

Resolving a P1851 code typically involves several potential solutions depending on the underlying cause:

Change Transmission Fluid and Filter: If dirty or low fluid is identified, changing the fluid and filter can often resolve issues related to slippage and erratic behavior.
Repair or Replace Wiring/Connectors: Damaged wiring should be repaired or replaced to restore proper electrical connections.
Replace Brake Band Apply Solenoid: If testing reveals a faulty solenoid, replacement is necessary to restore normal operation.
Service Valve Body: If clogged passages are identified, servicing or replacing the valve body may be required.

Cost Estimates

The cost of repairs associated with a P1851 code can vary widely based on several factors:

Transmission Fluid Change: $100 – $300 depending on vehicle type and service provider.
Solenoid Replacement: $150 – $500 including parts and labor.
Wiring Repairs: $50 – $200 depending on extent of damage.
Valve Body Service/Replacement: $300 – $800 depending on complexity and labor costs.

Warnings and Recommendations

It is crucial not to ignore a P1851 code as it can lead to more severe transmission issues over time.
Always consult your vehicle’s service manual for specific diagnostic procedures tailored to your model.
If unsure about any step in diagnosis or repair, seek professional assistance from a qualified mechanic.

Frequently Asked Questions About P1851

What does the P1851 code mean?
The P1851 code indicates a problem with the brake band apply solenoid performance or an issue with the transfer case contact plate.
Can I drive my car with a P1851 code?
You can drive temporarily, but it’s advisable to address it soon as it may worsen drivability and lead to more significant repairs.
How do I clear a P1851 code?
You can clear the code using an OBD-II scanner after addressing any underlying issues.
What are common symptoms of a failing brake band apply solenoid?
Common symptoms include slipping gears, delayed shifts, and erratic transmission behavior.
How serious is a P1851 trouble code?
The seriousness depends on underlying issues; if ignored, it can lead to severe transmission damage.
What should I check first when diagnosing a P1851 code?
Start by checking the transmission fluid level and condition as it often reveals underlying problems.
Is it safe to drive with this trouble code?
While it might be safe temporarily, continued driving could exacerbate existing problems.
When should I seek professional help?
If you are unable to diagnose or fix the issue after basic troubleshooting, it’s best to consult a professional mechanic.

In conclusion, addressing the P1851 trouble code promptly is essential for maintaining your vehicle’s performance. Understanding its meaning, recognizing symptoms, conducting thorough diagnostics, and implementing appropriate solutions will help ensure your vehicle remains reliable and safe on the road. Always prioritize safety by consulting professional help when necessary.