What it means
Electrical fault on the transmission fluid pressure sensor B circuit. Sensor B monitors a secondary hydraulic circuit such as a clutch line.
At a glance
- Usually lights the check-engine light
How it works
Transmission pressure sensor or switch B monitors a hydraulic pressure channel separate from sensor A and sends its signal to the control module for shift control. P0845 indicates an electrical fault in the B circuit, but does not by itself identify whether the sensor, wiring, connector, or another circuit component is at fault.
Common causes
Most likely first.
- Sensor failed
- Wiring fault
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 data and related transmission codes to see when the B circuit fault occurred.
- Check the transmission fluid level and condition using the manufacturer’s procedure, and note leaks that could affect hydraulic operation.
- Inspect sensor B’s connector and harness for loose terminals, corrosion, fluid intrusion, or damaged insulation.
- Use the wiring diagram to test sensor B’s supply, ground, and signal circuit for opens, shorts, or poor connections.
- Compare sensor B’s signal with the manufacturer’s specification under the applicable conditions before deciding whether the sensor or wiring needs repair.
Common fixes
- Reconnect and secure a loose sensor B connector.
- Repair damaged wiring or corroded terminals in the B circuit.
- Correct a low fluid level and repair any leak using the specified procedure and fluid.
- Replace sensor B if its electrical output is outside specification and its circuit tests correctly.
Can I keep driving?
If shifting is normal, keep any necessary trip short and gentle, and avoid towing or hard acceleration until the B circuit is checked. Stop driving if the transmission slips, loses drive, or shifts harshly, since continued use can worsen internal 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.