P0845
Transmission Fluid Pressure Sensor/Switch B Circuit
If your vehicle's onboard computer has flagged the diagnostic trouble code P0845, it refers to a detected anomaly regarding "Transmission Fluid Pressure Sensor/Switch B Circuit". This systemic engine fault needs a targeted check before symptoms expand.
Driver's Summary
Code P0845 means your vehicle detected a problem with the transmission fluid pressure sensor/switch b circuit system. You may notice check engine light, harsh downshifts, transmission shudder, all of which are direct consequences of this malfunction. Given the high severity of this code, continuing to drive risks significant mechanical damage. Have it diagnosed immediately.
Symptoms
Check engine light, harsh downshifts, transmission shudder
Common Causes
- Failed TFP Sensor B
- Short or open in sensor B circuit
- Dirty fluid blocking sensor port
- Valve body failure
How to Fix
- 1 Replace TFP Sensor B
- 2 Repair wiring harness
- 3 Clean valve body and change fluid
- 4 Replace valve body
Technical Explanation
To set P0845, the PCM samples the affected circuit multiple times per second, comparing live readings against manufacturer-programmed operating windows. Shift solenoid circuits are monitored for both functional performance (does the transmission achieve the commanded gear ratio?) and electrical integrity (is the solenoid's resistance within the normal range of 10–40 ohms?). Once confirmed, the code is stored as a permanent DTC and the MIL is activated. The freeze frame snapshot — recording RPM, load, coolant temperature, and fuel trim at fault detection — is also saved and is critical for accurate diagnosis.
Is It Safe to Drive?
Driving with an active P0845 fault risks accelerating damage to failed tfp sensor b and related components. The longer the fault persists, the more expensive the eventual repair becomes — what starts as a sensor or solenoid issue can escalate to major mechanical failure.
Mechanic's Pro Tip
For P0845, test the solenoid's coil resistance with a multimeter before ordering parts — most solenoids should read between 14 and 40 ohms; an open (infinite resistance) or short (near zero) confirms it's failed electrically. Also verify the PCM is commanding the solenoid by backprobing the connector with a test light during the relevant operating condition — if there's no command signal, the fault is in the PCM or wiring, not the solenoid itself.
Sensor replacement: $200 - $500; Valve body: $600 - $900