Faulty transmission fluid pressure sensor or switch reading high or stuck; Signal wire shorted to voltage or to the reference supply; Damaged, corroded or loose connector at the sensor or transmission control module; Contaminated, degraded or incorrect level of transmission fluid affecting pressure or the sensor; Valve body or solenoid fault causing genuinely excessive line pressure; Faulty transmission control module; Outdated control module software that is a known cause for the model.

P0843

Transmission Fluid Pressure Sensor/Switch A Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
8: AreaTransmission
43: FaultThe specific fault in that area

What it means

P0843 means the transmission control module has detected that the signal from transmission fluid pressure sensor or switch 'A' is higher than expected. The module saw a voltage or switch state above the normal range, which can point to an electrical fault or to a genuine hydraulic pressure problem. Which sensor is 'A' and where it sits depends on the model and transmission.

Symptoms

Gearbox warning light or malfunction indicator lamp on
Harsh, delayed or flared gear shifts
Transmission stuck in limp mode or a fixed gear
Slipping or poor acceleration
Erratic or incorrect gear selection
Reduced fuel economy

Possible causes

Faulty transmission fluid pressure sensor or switch reading high or stucklikely
Signal wire shorted to voltage or to the reference supplylikely
Damaged, corroded or loose connector at the sensor or transmission control modulelikely
Contaminated, degraded or incorrect level of transmission fluid affecting pressure or the sensorpossible
Valve body or solenoid fault causing genuinely excessive line pressurepossible
Faulty transmission control modulerare
Outdated control module software that is a known cause for the modelrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including gear, fluid temperature and vehicle speed
Check for related transmission codes and any manufacturer technical bulletins for the model and transmission
Inspect the sensor wiring and connectors for chafing, fluid ingress, corrosion, bent pins and poor retention
Check transmission fluid level, condition and type against the manufacturer specification, using the correct procedure for the model
Using live data, compare the sensor reading with the expected value at key on, engine off and at idle in different gear selections
Test the sensor reference supply, ground and signal circuit for short to voltage, short to supply and resistance faults against the wiring diagram
Check the sensor or switch itself against the specification for the transmission, as the method varies by model
If the electrical side is sound, carry out a line pressure test as the manufacturer specifies to rule out a hydraulic fault

How to fix

Replace the faulty fluid pressure sensor or switch and clear the code
Repair or replace damaged wiring and clean or replace faulty connectors
Correct the fluid level or replace degraded fluid and filter with the specified type, where the model allows
Repair or replace the valve body or faulty solenoids if pressure is genuinely too high
Update the control module software if a bulletin identifies it as a cause, or replace the module if it is confirmed faulty

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but limp mode and harsh shifts can stress the gearbox, so get it checked soon. Avoid heavy loads and towing, and stop if the gearbox slips badly or will not select gears.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.