Transmission Fluid Pressure Sensor/Switch C Circuit Intermittent
Your transmission's fluid pressure sensor is sending inconsistent signals to the engine computer, like a flickering light switch that won't stay in one position. This causes the transmission to behave unpredictably because it can't reliably measure how much hydraulic pressure is available.
The ECM monitors voltage or resistance signals from the transmission fluid pressure sensor (C circuit) to determine actual hydraulic pressure. The sensor signal should be stable and proportional to transmission pressure. An intermittent fault means the signal drops out or becomes erratic, preventing accurate pressure confirmation.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor voltage | 0.5–4.5V (varies by design) | Signal dropout, spikes, or below 0.1V/above 4.8V intermittently |
| Pressure correlation | Voltage matches actual line pressure | Signal stops matching pressure state |
Code P0874 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, P0874 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.