P0845 Code: Here's How to Solve It Fast

The P0845 trouble code is a generic powertrain code related to the transmission system. It specifically indicates an issue with the Transmission Fluid Pressure Sensor/Switch "B" Circuit. When your vehicle's computer detects an abnormal voltage reading from this sensor circuit, it triggers the P0845 code. This can lead to various transmission-related problems and potentially affect your vehicle's performance and safety.

P0845 Code Meaning	P0845 Code Common Causes
Abnormal voltage in Transmission Fluid Pressure Sensor/Switch "B" Circuit	Faulty transmission fluid pressure sensor
Transmission Control Module (TCM) detects circuit malfunction	Damaged or corroded wiring in the sensor circuit
Indicates potential transmission fluid pressure issues	Low or contaminated transmission fluid
May affect transmission shifting and overall performance	Internal transmission mechanical problems
Can trigger limp mode in some vehicles	Faulty Transmission Control Module (TCM)

Understanding the P0845 Code

The P0845 code is set when the Powertrain Control Module (PCM) or Transmission Control Module (TCM) detects a problem with the Transmission Fluid Pressure Sensor/Switch "B" Circuit. This sensor plays a crucial role in monitoring the transmission fluid pressure, which is essential for proper transmission operation and shifting.

Symptoms of P0845 Code

When your vehicle triggers the P0845 code, you may experience one or more of the following symptoms:

1. Illuminated Check Engine Light
2. Transmission shifting issues (harsh, delayed, or erratic shifts)
3. Vehicle entering limp mode (limited performance and speed)
4. Reduced fuel efficiency
5. Transmission slipping or failing to engage gears properly
6. In some cases, no noticeable symptoms other than the code itself

Technical Explanation

The Transmission Fluid Pressure Sensor/Switch "B" is responsible for monitoring the pressure of the transmission fluid in a specific circuit or line within the transmission. This information is crucial for the TCM to determine when to shift gears and how much pressure to apply to various transmission components.

When the PCM or TCM detects a voltage reading from this sensor that falls outside the expected range, it sets the P0845 code. This could indicate a problem with the sensor itself, the wiring connecting the sensor to the control module, or issues within the transmission that are affecting fluid pressure.

Diagnosing the P0845 Code

To properly diagnose the P0845 code, follow these steps:

1. Verify the code: Use an OBD-II scanner to confirm the P0845 code and check for any additional codes that may be present.
2. Check the transmission fluid: - Ensure the vehicle is on level ground and warmed up to operating temperature. - Locate the transmission dipstick and check the fluid level and condition. - If the fluid is low, top it off with the manufacturer-recommended type. - If the fluid appears dark, dirty, or has a burnt smell, a transmission fluid change may be necessary.
3. Inspect the wiring and connections: - Locate the Transmission Fluid Pressure Sensor/Switch "B" (consult your vehicle's service manual for the exact location). - Check for any visible damage, corrosion, or loose connections in the wiring harness and connectors. - Repair or replace any damaged components as needed.
4. Test the sensor circuit: - Disconnect the sensor connector. - Use a digital multimeter to check for proper voltage and ground at the connector. - Typical voltage should be either 5V or 12V, depending on the vehicle manufacturer. - If voltage is incorrect, there may be an issue with the power supply or ground circuit.
5. Test the sensor itself: - With the sensor still disconnected, use an ohmmeter to check the resistance of the sensor. - Compare the readings to the manufacturer's specifications. - If the readings are out of range, the sensor may need to be replaced.
6. Check for internal transmission issues: - If all previous tests pass, the problem may be related to internal transmission problems affecting fluid pressure. - This may require professional diagnosis using specialized equipment.
7. Clear the code and test drive: - After making any repairs or replacements, clear the code using an OBD-II scanner. - Take the vehicle for a test drive to see if the code returns.

Solutions for P0845 Code

Depending on the root cause of the P0845 code, one or more of the following solutions may be necessary:

1. Replace the Transmission Fluid Pressure Sensor/Switch "B"

If the sensor itself is faulty, replacing it is often the most straightforward solution.

Cost estimate: $50 to $200 for the sensor, plus 1-2 hours of labor ($100-$200)

Steps:

1. Locate the sensor (refer to your vehicle's service manual)
2. Disconnect the battery to prevent electrical issues
3. Unplug the electrical connector from the sensor
4. Remove the old sensor (may require special tools)
5. Install the new sensor, ensuring proper torque
6. Reconnect the electrical connector and battery
7. Clear the code and test drive the vehicle

Warning: Ensure you use the correct sensor for your specific vehicle make and model. Using an incorrect sensor can lead to further issues and potentially damage the transmission.

2. Repair or Replace Wiring and Connectors

If the issue is related to damaged wiring or connectors, repairing or replacing these components may solve the problem.

Cost estimate: $50 to $300, depending on the extent of the damage and labor involved

Steps:

1. Identify the damaged wiring or connectors
2. Disconnect the battery
3. Repair or replace the affected wiring or connectors
4. Use heat-shrink tubing or electrical tape to insulate any repairs
5. Reconnect the battery
6. Clear the code and test drive the vehicle

Warning: Proper electrical repair techniques are crucial to prevent short circuits or further damage. If you're not confident in your electrical repair skills, consult a professional.

3. Transmission Fluid Service

If the transmission fluid is low, contaminated, or old, a complete transmission fluid service may be necessary.

Cost estimate: $100 to $400, depending on the vehicle and type of service

Steps:

1. Warm up the vehicle to operating temperature
2. Locate the transmission drain plug and drain the old fluid
3. Remove and clean or replace the transmission filter (if applicable)
4. Reinstall the drain plug and refill with the correct type and amount of transmission fluid
5. Start the engine and check for leaks
6. Clear the code and test drive the vehicle

Warning: Use only the transmission fluid specified by your vehicle manufacturer. Using the wrong type of fluid can cause severe transmission damage.

4. Internal Transmission Repair

If the P0845 code is caused by internal transmission issues, such as worn components or a malfunctioning valve body, more extensive repairs may be required.

Cost estimate: $500 to $3000+, depending on the specific issue and whether a rebuild is necessary

Steps: Due to the complexity of internal transmission repairs, this job is best left to professional mechanics with specialized tools and expertise.

Warning: Attempting internal transmission repairs without proper knowledge and tools can result in severe damage to your vehicle's transmission.

5. Replace Transmission Control Module (TCM)

In rare cases, a faulty TCM may be the cause of the P0845 code. This is typically considered only after all other potential causes have been ruled out.

Cost estimate: $300 to $1000+, depending on the vehicle make and model

Steps:

1. Confirm that the TCM is the issue through comprehensive diagnostic testing
2. Obtain the correct replacement TCM for your vehicle
3. Disconnect the battery
4. Locate and remove the old TCM
5. Install the new TCM
6. Reconnect the battery
7. Program or flash the new TCM with the correct software (may require dealer-level equipment)
8. Clear codes and test drive the vehicle

Warning: TCM replacement and programming often require specialized equipment and knowledge. Improper installation or programming can cause severe transmission issues.

Preventing Future P0845 Codes

To help prevent future occurrences of the P0845 code:

1. Regularly check and maintain proper transmission fluid levels
2. Follow the manufacturer's recommended transmission service intervals
3. Address any transmission-related issues promptly
4. Avoid aggressive driving habits that can stress the transmission
5. Use only the recommended transmission fluid for your vehicle

Remember: While some P0845 code fixes can be performed by experienced DIY mechanics, many transmission-related issues require professional diagnosis and repair. If you're unsure about any step in the diagnostic or repair process, consult a certified mechanic to avoid potentially costly mistakes.

Closing Thoughts

The P0845 code, while potentially serious, is often resolvable with proper diagnosis and repair. By understanding the possible causes and following a systematic approach to diagnosis, you can often identify and fix the issue without resorting to major transmission repairs. However, it's crucial to address this code promptly to prevent potential damage to your vehicle's transmission and ensure safe, efficient operation.

Frequently Asked Questions About P0845

• Can I drive my car with the P0845 code?
  While the vehicle may still operate, it's not recommended to drive long distances with this code active. The code indicates a transmission issue that could worsen and lead to more expensive repairs if ignored.
• How urgent is it to fix a P0845 code?
  It's important to address this code as soon as possible. Transmission-related issues can quickly escalate, potentially leading to complete transmission failure if left unattended.
• Will the P0845 code clear itself?
  In most cases, the code will not clear itself. Even if the issue temporarily resolves, the code will likely remain stored in the vehicle's computer until it is cleared with a scan tool.
• Can low transmission fluid cause the P0845 code?
  Yes, low transmission fluid can potentially trigger the P0845 code. Low fluid levels can affect transmission pressure, which this sensor monitors.
• How much does it typically cost to fix a P0845 code?
  Costs can vary widely, from about $100 for a simple fluid change to $3000 or more for internal transmission repairs. The exact cost depends on the root cause and the specific vehicle.
• Can a P0845 code be caused by a recent transmission fluid change?
  Yes, if the wrong type of fluid was used or if air was introduced into the system during the change, it could potentially trigger this code.
• Is the P0845 code specific to certain vehicle makes or models?
  While P0845 is a generic code that can appear in many vehicles, some makes and models may be more prone to this issue due to specific design characteristics.
• Can I replace the transmission fluid pressure sensor myself?
  If you have moderate mechanical skills and the proper tools, you may be able to replace the sensor yourself. However, the sensor's location can be challenging to access in some vehicles, and proper diagnosis is crucial before replacement.