P0847 OBD-II Trouble Code: Transmission Fluid Pressure Sensor/Switch “B” Circuit Low

diagnostic check engine light

P0847 code definition

The P0847 trouble code detects an issue with the transmission fluid pressure sensor “B” circuit.

What the P0847 code means

The P0847 code is a standard OBD-II trouble code that detects a problem with the transmission fluid pressure “B” circuit. The “B” represents an area of the transmission fluid pressure circuit, rather than an individual component. The vehicle’s automatic transmission relies on electronic pressure control solenoids to manage the hydraulic pressure, which is used to help the vehicle shift, and to aid torque converter lockup. The solenoids are controlled by the powertrain control module (PCM), which uses a host of information (such as engine speed, throttle position, and vehicle speed) to determine the ideal amount of fluid pressure. When the desired fluid pressure level and the actual fluid pressure level do not match, the PCM will store the P0847 trouble code.

What causes the P0847 code?

A handful of different issues can cause the P0847 code to be triggered, including:

  • Defective electronic pressure control solenoid
  • Defective transmission fluid pressure sensor
  • Malfunctioning electronic pressure regulator
  • Insufficient transmission fluid levels
  • Dirty transmission fluid
  • Mechanical issues within the internal transmission
  • Hydraulic blockages in the fluid passages of the internal transmission
  • Defective hydraulic pump
  • Malfunctioning PCM
  • Malfunctioning transmission control module

What are the symptoms of the P0847 code?

The P0847 trouble code will often be accompanied by the check engine soon Warning Light illuminating on the vehicle’s instrument panel. The car may also experience severe transmission problems, such as slippage, harsh shifting, overheating, and even a total inability to shift. The PCM may also put the transmission in “limp-in” mode. Furthermore, the torque converter clutch may fail to work, and the vehicle is likely to experience a decrease in fuel efficiency.

How does a mechanic diagnose the P0847 code?

The P0847 code should be assessed with the assistance of a standard OBD-II trouble code scanner. A reputable technician can use the scanner to look at the freeze frame data, which will allow them to examine the P0847 code and note any additional trouble codes that are present. If there are numerous codes present, they should be addressed in the order in which they appear. Next, the mechanic can reset the trouble codes and restart the vehicle, to see if the code returns. If the code does not remain detected after the reset, then it was possibly detected erroneously, or signals an intermittent error.

If the P0847 trouble code remains detected following the reset, then the mechanic should begin with a few visual inspections. First, the transmission fluid should be checked to make sure that the levels are sufficient, and the fluid is clean. Fluid should be replaced or refilled as needed, unless it is severely contaminated, in which case there is likely serious damage in the transmission. Next, all electrical components (such as wires and connectors) should be checked, and the damaged ones should be replaced.

If the issue has not been resolved to this point, a manual pressure gauge can be hooked up to the transmission hydraulic system. This gauge will tell the mechanic if there is an issue with hydraulic fluid pressure, which would signal a defective solenoid, sensor, pump, or regulator, or hydraulic blockages in the passageways. If the problem is still unresolved, the technician will have to do a thorough inspection of the internal transmission, and possibly the control modules.

After any damage is noted and components are replaced, the mechanic will need to reset the trouble codes and restart the vehicle, to once again check if the codes return. By doing this, the mechanic is able to identify what the cause of the P0847 code was, and keep from making unnecessary repairs.

Common mistakes when diagnosing the P0847 code

The most common mistake that is made when diagnosing the P0847 code is the failure to comply with the OBD-II trouble code diagnosis protocol. The protocol should be followed step by step at all times, as this ensures an efficient and accurate diagnosis and repair.

It is common for high pressure pumps to be replaced erroneously, when something such as a sensor or an electrical component was the actual issue.

How serious is the P0847 code?

A vehicle that has a detected P0847 trouble code will usually still be drivable. However, the P0847 code usually results in poor transmission performance, and can do severe damage to the transmission if it is not taken care of. For these reasons, the P0847 code should always be addressed promptly.

What repairs can fix the P0847 code?

Some repairs for the P0847 trouble code are:

Additional comments for consideration regarding the P0847 code

The P0847 trouble code only applies to vehicles with automatic transmissions.

PCM and transmission control module failure are rare, and should only be considered when all other options are exhausted. If either of these control modules does need to be replaced, they will also need to be reprogrammed.

Need help with a P0847 code?

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The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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