What it means
The transmission fluid pressure sensor A circuit reports voltage above threshold, indicating short to power or open ground.
At a glance
- Usually lights the check-engine light
How it works
Transmission pressure sensor or switch A supplies a voltage signal that the control module uses to monitor hydraulic pressure. P0843 sets when the A circuit voltage rises above its calibrated limit, which can result from a signal short to power, an open ground reference, or a sensor or connector fault.
Common causes
Most likely first.
- Signal shorted to battery
- Open ground reference
- Connector pins corroded - high contact resistance
Symptoms
- Transmission warning light may be on
- Shifting may be abnormal
How to diagnose it
- Record freeze-frame data and inspect sensor A live voltage or pressure data to confirm whether the reported signal is high when the fault occurs.
- Inspect the A sensor connector and harness for loose or corroded terminals, fluid intrusion, or wiring rubbed through against a powered circuit.
- Using the wiring diagram, check for an open ground reference and test the signal wire for a short to power.
- Measure the sensor A supply, ground, and signal under the specified conditions and compare them with the manufacturer’s specification.
- If wiring and grounds are sound, test sensor A for an internal fault using the manufacturer’s diagnostic procedure.
Common fixes
- Reconnect the sensor A connector and repair corroded terminals or damaged seals.
- Repair a signal wire shorted to power or restore an open ground reference.
- Replace sensor A if the circuit is correct but its signal remains above specification.
- Secure the repaired harness away from heat, moving parts, or sharp edges.
Can I keep driving?
Drive only as needed and gently until the high A-circuit signal is diagnosed; avoid towing and hard acceleration. If shifting becomes harsh or the transmission slips or loses drive, stop driving because continued operation may damage internal components.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.