What it means
The transmission fluid pressure sensor/switch B reports a circuit high fault. Hydraulic pressure feedback for shift control is unreliable on this channel.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Transmission pressure sensor or switch B provides a voltage signal for the control module’s monitoring of its hydraulic pressure channel. P0848 sets when the B circuit voltage exceeds the calibrated limit, which may be caused by a signal short to battery power, an open sensor circuit, or a connector fault.
Common causes
Most likely first.
- Signal wire shorted to B+
- Open sensor
- Connector pins corroded - high contact resistance
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Record freeze-frame data and review sensor B live voltage or pressure data to confirm the high signal and the conditions when it occurs.
- Inspect sensor B’s connector and harness for loose or corroded terminals, fluid intrusion, or damage that could interrupt the circuit.
- Using the wiring diagram, test the B signal wire for a short to power and check for an open sensor connection.
- Measure the B sensor supply, ground, and signal under the specified conditions and compare them with the manufacturer’s specification.
- If the wiring checks out, test sensor B for an internal open or other fault using the vehicle’s diagnostic procedure.
Common fixes
- Reconnect sensor B and repair loose, corroded, or damaged connector terminals.
- Repair a signal wire short to battery power or an open in the B circuit.
- Replace sensor B if its output remains high with sound wiring and connections.
- Secure repaired wiring to prevent rubbing or strain.
Can I keep driving?
A high B-circuit signal may cause abnormal shifts or limp mode, so avoid towing, hard acceleration, and unnecessary driving until it is diagnosed. Stop if the transmission slips, loses drive, or becomes stuck in one gear, because continued operation may worsen damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.