P0847
Transmission Fluid Pressure Sensor/Switch B Circuit Low
Powertrain Transmission Control Pressure Sensor Circuit 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

The transmission fluid pressure sensor is sending a signal that's too weak or missing entirely, like a dimly lit warning light that's hard to see. This tells the engine computer that transmission pressure is dangerously low or the sensor circuit is broken.

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Symptoms You May Notice
3 known symptoms for this code
Transmission slipping or delayed shifts
Limp mode or reduced engine power
Check Engine Light illuminated
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECM monitors the voltage output from the transmission fluid pressure sensor B circuit. It expects a voltage signal within a specific range that correlates to actual fluid pressure. When the voltage drops below the minimum threshold, the ECM logs a low circuit fault.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Sensor voltage output 0.5 - 4.5 volts (varies by pressure) Below 0.2 volts or open circuit
Fluid pressure interpretation 20-300 psi depending on gear Below minimum expected for current gear
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Wiring harness connector
Inspect and clean the sensor connector; corrosion or loose pins often cause low voltage signals.
2
Transmission fluid
Check fluid level and top up if low; insufficient fluid reduces pressure and sensor signal strength.
3
Transmission fluid pressure sensor B
Replace the faulty sensor if voltage readings remain out of spec after cleaning connections.