What it means
The transmission fluid pressure sensor/switch B reports a circuit range/performance 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 reports hydraulic pressure on its monitored channel to the control module. P0846 sets when the B signal is within a plausible electrical range but does not track expected pressure behavior during the specified conditions, which may reflect sensor drift, aerated fluid, or a hydraulic pressure issue.
Common causes
Most likely first.
- Sensor offset drifted
- Aerated fluid affects pressure
- Sensor element aged beyond calibration window
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 compare sensor B live data with commanded pressure or the available related pressure readings to identify when they disagree.
- Check fluid level and condition using the manufacturer’s procedure, looking for low or aerated fluid and any leaks.
- Inspect sensor B’s connector and wiring for corrosion, loose terminals, or damage that could make the signal inaccurate.
- Test the B circuit’s supply, ground, and signal against the manufacturer’s specification under the specified conditions.
- If the circuit is sound, check actual hydraulic pressure using the vehicle’s prescribed test to separate sensor drift from a pressure problem.
Common fixes
- Correct low fluid and repair any leak using the specified procedure and fluid.
- Repair a loose or corroded sensor B connection or damaged wiring.
- Replace sensor B if its output is inaccurate while the circuit and actual pressure are within specification.
- Repair a confirmed hydraulic pressure fault or source of fluid aeration.
Can I keep driving?
This fault can cause harsh or delayed shifts and may put the transmission into limp mode, so avoid towing, hard acceleration, and unnecessary driving. Stop if it slips, loses drive, or becomes stuck in one gear; continuing may damage internal transmission parts.
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.