Transmission Fluid Pressure Sensor/Switch A Circuit High
What does P0843 mean?
The P0843 code means the vehicle's onboard diagnostic system has detected: Transmission Fluid Pressure Sensor/Switch A Circuit High. This is a moderate severity code.
Common Symptoms
- Check Engine Light illuminated
- Harsh or firm shifts
- Transmission may not upshift properly
- Vehicle may enter limp mode
Probable Causes (Ranked by Likelihood)
- Open circuit in pressure sensor A ground wire Very High
- Faulty pressure sensor A reading high High
- Short to voltage in sensor signal wire Moderate
- TCM reference voltage issue Low
Step-by-Step Diagnostic Procedure
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Measure voltage at the pressure sensor A connector with key on, engine off
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Check for an open ground wire at the sensor
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Test for short to battery voltage on the signal wire
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Replace sensor A if wiring checks pass
Frequently Asked Questions
What causes a high signal from the pressure sensor?
A high signal typically means the sensor ground is open or the signal wire is shorted to battery voltage, causing the TCM to see a falsely high pressure reading.
Why does high pressure cause harsh shifts?
If the TCM believes pressure is too high, it may reduce solenoid duty cycles, which can actually cause unpredictable shift quality. The TCM relies on accurate pressure data for smooth shifts.
Is P0843 the opposite of P0842?
Yes, P0842 indicates a low signal and P0843 indicates a high signal from the same pressure sensor circuit. The causes are complementary.