P0848 OBD-II Trouble Code: Transmission Fluid Pressure Sensor/Switch B Circuit High

P0848 code definition

The storage of a P0848 trouble code means that the powertrain control module (PCM) has detected a problem with the transmission fluid sensor circuit. The pressure to the hydraulic pump is controlled by the PCM via the electronic pressure control solenoids. Some of the other trouble codes a mechanic might also see include P0845, P0846, P0847, and P0849.

What the P0848 code means

A P0848 trouble code signifies that there is a discrepancy in the pressure produced as opposed to what is actually needed by the transmission to function properly. The transmission needs the proper amount of pressure to shift properly and for the torque converter to engage and disengage like it should.

What causes the P0848 code?

Some common causes of a P0848 trouble code include a faulty transmission fluid pressure sensor, bad electronic pressure control solenoid, and blockage within the hydraulic lines of the transmission. Mechanical failure of the transmission can also lead to the storage of this code by the PCM. Mechanical failure can result from a low fluid condition or dirty and contaminated fluid within the transmission. A low fluid condition or dirty transmission fluid can also cause the PCM to store the trouble code. Though rare, another culprit could be the PCM itself.

What are the symptoms of the P0848 code?

In addition to showing no obvious symptoms of a problem at all, other than a lit Check Engine light, when storing a P0848 trouble code, the torque converter in the vehicle could fail to work properly, there could be problems with shifting, and the transmission could overheat. Other symptoms include a reduction in the fuel efficiency of the vehicle and the PCM placing the transmission into Limp-in mode.

How does a mechanic diagnose the P0848 code?

To properly diagnose a P0848 trouble code, a mechanic needs a code reader, digital volt/ohmmeter, manual pressure gauge, hydraulic pressure diagram, and the manufacturer's wiring diagram for the transmission fluid pressure sensor. The mechanic must also perform the following steps:

• Start by checking the vehicle's transmission fluid, paying particular attention to fluid condition and smell.
• If the fluid has a burnt smell or looks abnormal, remove the transmission pan and inspect it for the presence of debris, including parts of the clutch. If debris is found, rebuild the transmission before proceeding.
• Also visually inspect the wiring, connectors, and any related components for damage.
• Fix any detected leaks before filling the transmission with fluid. Also, clear the P0848 trouble code.
• Next, the mechanic should start the vehicle and allow it to reach a normal operating temperature before test driving it to see if the code returns.
• If the code returns, connect a manual pressure pump and using a hydraulic pressure diagram test the pressure produced by the hydraulic pump. The mechanic should then compare their findings to the manufacturer's specifications.
• If, after clearing the code, it returns, use a wiring diagram from the manufacturer for the transmission fluid pressure sensor and a digital volt/ohmmeter to check the reference voltage and ground signal of the sensor.
• If the sensor tests as open, disconnect any related control modules and test the circuits related to the transmission fluid pressure sensor for continuity and resistance.
• The mechanic should also check the reference voltage and ground signal of the electronic pressure control solenoid and PCM with the volt/ohmmeter for fault.
• Clear the P0848 trouble code and test the vehicle to see if it returns.

Common mistakes when diagnosing the P0848 code

A common mistake when diagnosing a P0848 trouble code is for the mechanic to overlook a faulty transmission fluid pressure sensor, electronic pressure control solenoid, or damaged wiring as the cause of the code and assuming it was stored in conjunction to a faulty high pressure pump when the pump is not the problem. Replacing the pump does not fix the problem and results in the trouble code returning.

How serious is the P0848 code?

Failure to repair a P0848 trouble code can result in no apparent problems with the vehicle to a complete failure of the transmission. Other problems vehicle owners can encounter when leaving a P0848 trouble code unfixed include problems shifting, slipping of the transmission, and the transmission becoming overheated.

What repairs can fix the P0848 code?

To repair a P0848 trouble code, the mechanic should perform the following:

• If the mechanic detects a damaged transmission due to debris in the transmission pan, then the transmission first needs rebuilding and a new torque converter installed.
• The mechanic should also replace any damaged or faulty wiring, connectors, or components.
• Before test driving the vehicle, the mechanic needs to fill the transmission to a level appropriate to allow them to fix any leaks.
• If further testing shows that the hydraulic pump is bad, the mechanic needs to replace the pump. This requires the removal of the transmission and for the mechanic to partially disassemble it.
• The mechanic should likewise replace any bad transmission fluid pressure sensors or electronic pressure control solenoids.
• Finally, if the PCM tests as bad, the mechanic needs to replace that as well, making sure to reprogram it in the process.

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