P0847 Code: Complete DIY Repair Guide

The P0847 trouble code is a diagnostic trouble code (DTC) that indicates an issue with the transmission fluid pressure sensor or switch “B” circuit being low. This code is part of the OBD-II (On-Board Diagnostics II) system, which monitors the performance of various vehicle systems, including the engine and transmission. When the powertrain control module (PCM) detects that the voltage from the transmission fluid pressure sensor does not match expected values, it triggers this code. Understanding and addressing the P0847 code is crucial for maintaining optimal transmission performance and ensuring the longevity of your vehicle.

Symptoms of P0847 Code

The symptoms associated with the P0847 trouble code can vary based on the underlying issue but commonly include:

• Malfunction Indicator Light (MIL): The check engine light will illuminate on your dashboard.
• Change in Shift Quality: You may experience rough or erratic shifting as the transmission struggles to adjust to incorrect fluid pressure readings.
• Limp Mode Activation: The vehicle may start in second or third gear to prevent further damage, limiting acceleration.
• Reduced Fuel Economy: Inefficient shifting can lead to increased fuel consumption.
• Transmission Slipping: You might notice that the vehicle hesitates or slips during acceleration.

Technical Explanation

The P0847 code specifically refers to a malfunction in the “B” circuit of the Transmission Fluid Pressure Sensor (TFPS). The TFPS monitors the hydraulic pressure within the transmission, which is essential for proper shifting and overall transmission function. The PCM uses this information to adjust shift points and maintain optimal performance. When there is a discrepancy between expected and actual fluid pressure readings, it indicates a potential fault in the sensor, wiring, or even internal components of the transmission.

Step-by-Step Diagnosis

To effectively diagnose a P0847 code, follow these steps:

1. Initial Scan: Use an OBD-II scanner to confirm that P0847 is present and check for any additional codes that may provide more context.
2. Visual Inspection:

• Inspect wiring and connectors related to the TFPS for signs of damage, corrosion, or loose connections.
• Check the condition of the transmission fluid; it should be clean and at proper levels.

1. Voltage Testing:

• With the ignition on but the engine off, use a digital voltmeter to measure voltage at the TFPS connector.
• The voltage should typically read between 5V and 12V based on manufacturer specifications.

1. Resistance Testing:

• Disconnect the TFPS connector and measure resistance across its terminals using an ohmmeter.
• Compare readings against manufacturer specifications; if they are out of range, replace the sensor.

1. Hydraulic Pressure Check:

• If previous tests pass but P0847 persists, connect a manual pressure gauge to assess hydraulic pressure in the system.
• Low or inconsistent readings could indicate issues with solenoids or internal blockages.

1. Professional Assessment:

• If all tests are inconclusive, consult with a professional mechanic who can perform more advanced diagnostics such as scanning for PCM faults or internal transmission issues.

Solution Methods

To resolve issues related to a P0847 code, consider these solutions:

• Replace Faulty TFPS: If testing confirms that the sensor is faulty, replacing it is often straightforward and can resolve erroneous readings.
• Repair Electrical Issues: Fix any damaged wiring or connectors found during inspection. Corrosion can often be cleaned with electrical contact cleaner.
• Check Transmission Fluid Levels: Ensure that fluid levels are adequate; top off if necessary. If fluid appears dirty or contaminated, consider a complete flush.
• Inspect Solenoids and Internal Components: If hydraulic pressure checks indicate problems, solenoids may need replacement, or further inspection of internal components may be required.
• Replace PCM if Necessary: In rare cases where all other components are functioning correctly, a faulty PCM may need replacement; ensure it is programmed correctly for your vehicle model.

Cost Estimates

The costs associated with diagnosing and repairing a P0847 code can vary widely based on location and vehicle type:

• Diagnostic Fees: Typically range from $100 to $150 at most shops for a thorough diagnostic check.
• Transmission Fluid Replacement: Expect to pay between $100 and $200 depending on fluid type and labor costs.
• TFPS Replacement: Parts can range from $50 to $150, with labor adding another $50 to $100.
• Solenoid Replacement: Costs can range from $100 to $300 depending on whether it’s part of a larger assembly or standalone.

Warnings and Recommendations

• Always disconnect battery power before working on electrical components to prevent shorts or other electrical issues.
• If you are uncomfortable performing any of these steps, seek assistance from a qualified mechanic; improper repairs can lead to further damage.
• Regular maintenance of your vehicle’s transmission fluid can help prevent issues like those indicated by P0847. Always follow manufacturer recommendations for fluid change intervals.

Frequently Asked Questions About P0847

• What does error code P0847 mean?
  P0847 indicates that there is a problem with the Transmission Fluid Pressure Sensor/Switch ‘B’ Circuit being low.
• Can I drive my car with a P0847 code?
  While it may be possible to drive short distances without immediate issues, it’s advisable to address this code promptly to avoid potential damage.
• How do I reset a P0847 code?
  You can reset it by using an OBD-II scanner after addressing any underlying issues; however, if not fixed, it will likely return.
• What are common causes of P0847?
  Common causes include faulty sensors, electrical circuit issues, low fluid levels, or internal mechanical problems in the transmission.
• Is it safe to ignore a P0847 code?
  No, ignoring this code could lead to more significant transmission problems over time.
• How often does P0847 occur?
  This code can occur in various vehicles but is more common in those with automatic transmissions due to their reliance on electronic controls.
• What tools do I need for diagnosing P0847?
  A digital voltmeter, ohmmeter, OBD-II scanner, and basic hand tools will be necessary for diagnosis.
• When should I seek professional help for P0847?
  If you have performed basic diagnostics without resolution or if you are uncomfortable performing repairs yourself.

In conclusion, understanding and addressing trouble codes like P0847 is crucial for maintaining your vehicle’s performance. By following proper diagnostic procedures and addressing any identified issues promptly, you can ensure your vehicle remains reliable while avoiding costly repairs down the line. Always prioritize safety and consult professionals when necessary.