Transmission Fluid Pressure Sensor/Switch C Circuit High
The transmission fluid pressure sensor is sending a signal that's too high, like a pressure gauge stuck on the maximum reading. This usually means a wiring problem, sensor failure, or internal transmission issue.
The ECM monitors voltage output from the transmission fluid pressure sensor (typically 0.5–4.5V range). When voltage exceeds the maximum threshold continuously, it triggers a high circuit fault. The ECU uses this signal to optimize shift timing and pressure modulation.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor Voltage | 0.5–4.5V (proportional to fluid pressure) | >4.5V or shorted high |
| Fluid Pressure Signal | 20–200 PSI range mapped to voltage | Signal indicates abnormally high pressure |
Code P0873 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, P0873 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.