Transmission Fluid Pressure Sensor/Switch B Circuit High
The P0848 code indicates that the Powertrain Control Module (PCM) or Transmission Control Module (TCM) has detected a high voltage condition in the transmission fluid pressure (TFP) sensor or switch 'B' circuit. This means the signal voltage from the sensor exceeds the maximum expected threshold for a specified amount of time, pointing to an electrical fault or abnormal internal pressure.
This code is considered high severity because incorrect transmission pressure readings can lead to harsh shifting, transmission slipping, or the vehicle entering limp mode. Driving with this condition for extended periods can cause severe internal transmission damage.
Common symptoms
- Illuminated Check Engine Light
- Harsh or erratic transmission shifting
- Transmission slipping between gears
- Vehicle entering limp mode (restricted to a single gear)
- Failure of the torque converter clutch to engage
Likely causes
- Defective transmission fluid pressure sensor/switch 'B'
- Low, dirty, or degraded transmission fluid
- Damaged, corroded, or shorted wiring in the sensor circuit
- Poor electrical connection at the sensor connector
- Internal transmission mechanical failure or valve body issue
- Faulty Transmission Control Module (TCM) or PCM (rare)
What to check before replacing parts
Check the transmission fluid level and condition.
Look for: Fluid that is low, burnt, or heavily contaminated, which can cause pressure anomalies and sensor malfunctions.
Visually inspect the wiring harness and connector for sensor 'B'.
Look for: Frayed wires, melted insulation, or corroded pins that could cause a short to voltage or an open circuit.
Scan for additional TCM codes and monitor live data.
Look for: The TFP sensor 'B' voltage reading stuck at a high value (e.g., near 5V) regardless of engine RPM or gear selection.
Test the sensor circuit with a digital multimeter.
Look for: Proper 5V reference and ground at the connector; a short to power on the signal wire indicates a wiring harness fault.
Test the transmission fluid pressure sensor directly.
Look for: Resistance values that are out of the manufacturer's specified range, indicating an internal open or failure within the sensor itself.
This page explains the generic P0848 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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