P0849
Transmission Fluid Pressure Sensor/Switch B Circuit Intermittent
Powertrain Transmission Control Fluid Pressure Sensor 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your transmission's fluid pressure sensor is sending inconsistent signals to the engine computer, like a flickering light switch. This intermittent connection prevents the transmission from properly monitoring fluid pressure.

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Symptoms You May Notice
3 known symptoms for this code
Transmission shifting harshly or unpredictably
Check Engine Light illuminated
Transmission may go into limp mode or safe mode
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors voltage signals from transmission fluid pressure sensor B to verify adequate hydraulic pressure for smooth shifting. When the signal drops in and out intermittently rather than showing a steady reading, the ECU cannot trust the sensor data and triggers the fault code.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Sensor voltage 0.5–4.5 volts (steady) Signal dropout or intermittent voltage spikes
Fluid pressure 20–120 PSI (vehicle dependent) Erratic readings or loss of signal
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Transmission fluid and filter
Low or contaminated fluid causes weak sensor signals; drain, replace filter, and refill to factory capacity.
2
Sensor connector and wiring harness
Inspect for corroded pins, loose connections, or damaged wires; clean or reseat connectors firmly.
3
Transmission fluid pressure sensor B
Replace the sensor if connector and fluid are good; sensor may have internal electrical faults.