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Home / DTC / P0845 — Transmission Fluid Pressure Sensor/Switch B Circuit

P0845 — Transmission Fluid Pressure Sensor/Switch B Circuit

Detailed page for trouble code P0845.

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P0845

Generic P — Powertrain

Transmission Fluid Pressure Sensor/Switch B Circuit

Brand: Generic
Type: P — Powertrain
Views: UK: 21 EN: 55 RU: 46
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Page language: EN

Causes

  • Open or shorted wiring in TFP sensor/switch B circuit
  • Faulty transmission fluid pressure sensor or pressure switch (B)
  • Poor connector contact or corrosion at sensor or PCM/TCM connector
  • Blown fuse or loss of reference voltage
  • Internal TCM/PCM driver fault
  • Intermittent wiring damage (chafing, broken wire)

Symptoms

  • Check Engine or Transmission warning light illuminated
  • Transmission may shift harshly, fail to shift, or go into limp/backup mode
  • Stored transmission-related diagnostic trouble codes
  • Unexpected line pressure behavior (slips, delayed engagement)
  • Possible fail-safe/reduced performance mode

What to check

  • Scan for codes and freeze-frame data; record any related transmission codes
  • Visual inspection of sensor, harness, and connectors for damage or corrosion
  • Check transmission fluid level and condition before connector tests
  • Verify battery voltage and fuses for transmission/PCM power circuits
  • Backprobe connector and monitor signal while operating transmission (safe conditions)

Signal parameters

  • Reference voltage (sensor power): typically ~5.0 V (±0.25 V) from PCM/TCM
  • Signal output (pressure sensor transducer): typically 0.2–4.8 V across full pressure range (varies by vehicle)
  • Switch-type pressure switch: closed continuity at high/low pressure (near 0–5 ohms) and open at opposite state (OL/infinite)
  • Ground: near 0 ohms continuity to PCM ground (
  • If the circuit is open: signal = floating/OL; if shorted to ground: signal ≈ 0 V; if shorted to battery: signal ≈ battery voltage

Diagnostic algorithm

  1. Connect a scan tool. Read and record DTC P0845 plus any other codes and freeze-frame data. Note operating conditions when code set.
  2. Perform a visual inspection of the sensor, harness, and connector for damage, corrosion, loose pins, or fluid intrusion. Repair any obvious damage.
  3. Check battery voltage and relevant fuses/relays. Replace blown fuses and retest.
  4. Identify wires for reference (5 V), signal, and ground at the sensor connector. With ignition ON (engine OFF), backprobe and verify reference ≈5 V and good ground continuity to PCM.
  5. With ignition ON and/or engine running (follow safe procedures), monitor the signal voltage. At rest and during a safe transmission pressure change (as specified by manufacturer or by cycling through gear selector with parking brake set), verify the signal changes within expected range (see signal_params).
  6. If switch-type, check continuity across switch terminals while varying transmission pressure (or during gear cycling) — should change state. For transducer type, check for a smooth voltage change with pressure.
  7. If signal is abnormal, inspect wiring continuity between sensor and PCM: check for opens, shorts to power, and shorts to ground using an ohmmeter with battery disconnected. Wiggle harness to look for intermittent faults.
  8. If wiring and connectors are good, swap or bench-test the sensor/switch if a known-good unit is available, or replace the sensor/switch with OEM-equivalent part.
  9. After repair, clear codes, perform a road test and monitor live data for proper sensor behavior and absence of code return.
  10. If wiring and sensor pass but fault persists, consider PCM/TCM driver failure — consult vehicle-specific service information before replacing module.

Likely causes

  • Corroded or loose connector at the TFP sensor/switch B
  • Open or short in sensor B signal/ground wiring
  • Failed TFP pressure sensor/switch B
  • Loss of reference voltage (fuse or PCM power feed)
  • Intermittent wiring (pin damage or terminal backout)

Fault status

⚠️ Status
TCM detected a fault on the transmission fluid pressure sensor/switch B circuit (open, short to ground/power, or intermittent). Diagnostic trouble code P0845 stored.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0 - 2.5 hours
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