Transmission Fluid Pressure Sensor/Switch A Circuit High
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.
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.
| 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 |
Code P0843 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0843 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.