The pressure switches found in your vehicle’s transmission are for feedback and shift timing. When the input from the transmission fluid pressure switch does not match the typical operating voltages stored in the powertrain control module (PCM), error code P0847 may be set.
Learn more about what code P0847 means, what causes it, and how you can fix it.
What Does Code P0847 Mean?
The P0847 error code stands for “Transmission Fluid Pressure Sensor/Switch "B" Circuit Low.” This diagnostic trouble code (DTC) is one among several codes in your vehicle’s On-Board Diagnostics II (OBD-II) system that indicate a problem with its transmission fluid pressure sensor/switch. Vehicle makes like Honda, Acura, and Nissan have been reported to store the P0847 code.
The transmission fluid pressure sensor/switch (TFPS) is typically located on the valve body inside the transmission, though in some cases, it may be mounted directly on the transmission case. This sensor's role is to convert mechanical transmission pressures into electrical signals, which are sent to the PCM or transmission control module (TCM).
The PCM or TCM uses the voltage signal from the TFPS to monitor transmission pressure and shifting activity, relaying this information to other controllers via the vehicle's communication network. Error code P0847 is triggered when the "B" circuit signal deviates from the expected voltage range stored in the PCM/TCM memory. This discrepancy could point to electrical circuit issues with the TFPS or, less commonly, internal mechanical transmission problems.
Manufacturers like Honda emphasize that P0847 typically results from electrical faults rather than mechanical transmission issues. When this code is stored, the vehicle may enter fail-safe mode, restricting gear shifting to specific gears (3rd or 6th) to protect the transmission.
What Causes Code P0847?
A variety of reasons can cause the error code P0847 to be stored. Some common causes include:
- Faulty TFPS
- Wiring problems
- Not enough transmission fluid
- Internal transmission mechanical issue
- Malfunctioning PCM or TCM
Faulty TFPS
A failing transmission fluid pressure sensor may send incorrect signals to the PCM/TCM, which may misinterpret the transmission’s pressure readings. This can also result in improper shifting.
Wiring Problems
Damaged, corroded, or loose wiring in the TFPS circuit can disrupt the flow of electrical signals. This can lead to voltage irregularities that trigger the P0847 code.
Not Enough Transmission Fluid
Low or insufficient transmission fluid can cause pressure drops within the system, leading to inaccurate readings from the TFPS.
Internal Transmission Mechanical Issue
Mechanical problems, such as worn-out components or blockages in the hydraulic system, can affect fluid pressure. This can result in the TFPS detecting abnormal readings.
Malfunctioning PCM or TCM
A defective PCM or TCM may misread the TFPS input or fail to process the data accurately.
What Are the Symptoms of Code P0847?
One of the most common symptoms of error code P0847 is an illuminated check engine light. Here are other, more specific symptoms you should also look out for:
- Different shift quality
- Bad fuel economy
- Incorrect transmission shifting
- Limp mode
Different Shift Quality
The vehicle may experience rough, delayed, or jerky gear shifts due to inaccurate transmission pressure readings from the TFPS. This often occurs because the transmission does not receive the right proper pressure feedback for smooth operation.
Bad Fuel Economy
Transmission problems may result in the engine consuming more fuel than necessary. This inefficiency significantly impacts the car’s fuel economy.
Incorrect Transmission Shifting
The transmission may shift into the wrong gears or fail to shift at all, as the PCM/TCM struggles to manage gear changes without reliable pressure data.
Limp Mode
Limp mode may be activated to prevent further damage when the transmission fluid pressure sensor/switch malfunctions. In this mode, the transmission is locked into a single gear, limiting speed and drivability.
How to Diagnose Code P0847
It’s possible to diagnose code P0847, even as a beginner, as long as you’re equipped with the right tools and knowledge for the job. Here are some common troubleshooting steps to diagnose code P0847:
Check Voltage
Turn on the ignition and measure the voltage at the TFPS using a voltmeter. Ensure it reads either 12 volts or 5 volts per manufacturer specifications; if incorrect, repair the power or ground wire or replace the PCM/TCM.
Test for Connection Stability
Gently wiggle the sensor connections while monitoring voltage. Check for signs of physical damage, corrosion, or misalignment. If the readings fluctuate, repair or replace faulty wiring or connectors.
Resistance Test
Connect an ohmmeter between the signal terminal and the ground or low reference terminal of the TFPS. Check the resistance against manufacturer specifications with no pressure applied; wiggle the connector to monitor changes.
Review Stored DTCs
Connect your OBD-II scanner to the appropriate port on your car. Then, the scanner will show every DTC that has been stored. Examine the saved codes to identify the source of the problem.
Check for Bad PCM
If the P0847 code persists even after replacing the TFPS, it may indicate a failed PCM/TCM or internal transmission issues.
How to Fix Code P0847
Keep in mind that there is no single solution for OBD-II codes. That said, here are some common fixes for the P0847 code:
Replace the Transmission Fluid Pressure Sensor/Switch
A malfunctioning sensor can send incorrect signals to the PCM/TCM, triggering the P0847 code. Replacing the faulty sensor/switch can restore accurate pressure readings and resolve the issue.
Fix or Replace Faulty Wiring or Connectors
Damaged or corroded wiring and connectors in the TFPS circuit can disrupt signal transmission, which in turn sets error code P0847. Repairing or replacing any compromised wiring or connectors can reestablish proper communication between the affected parts.
Ensure Functional Charging System
Low or fluctuating battery voltage impacts the electrical signals sent to and from the transmission range sensor. Ensure the battery is charged and the charging system is functioning properly to maintain consistent voltage.
Check and Maintain Adequate Transmission Fluid Levels
Low transmission fluid levels can lead to pressure inconsistencies, affecting sensor readings. Ensuring the transmission fluid is at the recommended level can help maintain proper functionality.
Fix Any Internal Transmission Mechanical Issues
Worn components or blockages can alter fluid pressure, so replacing these may resolve the stored error code.
Replace ECM/TCM/PCM
Although rare, a faulty ECM/PCM/TCM can misinterpret sensor signals, leading to erroneous codes. To fix this, test and, if necessary, reprogram or replace the faulty control module.
Other Codes Related to P0847
Other codes related to P0847 involve errors with the transmission fluid pressure sensor/switch. Here are some relevant DTC’s you should know about:
P0845
This code is set if the voltage input for the “B” circuit does not match the normal operating voltages stored in the PCM/TCM's memory.
P0846
Error code P0846 indicates that the PCM has detected an anomalous fluid reading from the transmission system.
P0848
Code P0848 is stored when the “B” input readings from the TFP sensor are different from the normal operating voltages programmed into the PCM's memory.
P0849
A stored P0849 indicates that the PCM has determined a problem with the pressure sensor, switch, or hydraulic clutch that identifies fluid levels inside the automatic transmission.
FAQ
Can you drive with a p0847 code?
Technically, you can drive a car with a stored P0847 code, but you are strongly advised against it as this error code means there is an issue with the transmission fluid pressure sensor or switch—and driving may become hazardous or challenging as a result.