P0843
Transmission Fluid Pressure Sensor/Switch A Circuit High
Powertrain Transmission Control Pressure Sensor Circuit 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your transmission fluid pressure sensor is reading too high, like a pressure gauge stuck on the wrong number. The ECU thinks there's excessive pressure when there might not be, triggering a warning light.

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Symptoms You May Notice
3 known symptoms for this code
Check Engine Light (MIL) illuminated
Transmission shifting delays or limp mode activation
Possible transmission overheating warning
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the transmission fluid pressure sensor voltage output to verify hydraulic pressure is within normal operating range. A high voltage signal indicates the sensor is reporting excessive pressure or has an open/short circuit. The ECM compares the signal against calibrated thresholds to detect electrical faults.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Sensor Voltage 0.5–4.5V (proportional to pressure) >4.8V or stuck high
Fluid Pressure 30–150 PSI (operating conditions) Signal indicates >160 PSI continuously
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Wiring harness connector
Inspect and reseat the sensor connector at the transmission for corrosion or loose pins.
2
Transmission fluid
Check and top up transmission fluid to proper level; low fluid can cause erratic sensor readings.
3
Transmission Fluid Pressure Sensor
Replace the faulty sensor if voltage remains high after connector and fluid checks.