Transmission Fluid Pressure Sensor/Switch Circuit High
The P0878 code indicates that the powertrain control module (PCM) has detected a voltage signal from the transmission fluid pressure sensor that is higher than the expected range. This sensor monitors hydraulic pressure inside the transmission to ensure proper shifting and line pressure control. A high circuit condition typically means there is a short to voltage, a faulty sensor, or a wiring issue. This can lead to harsh shifts, slipping, or limp mode.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or delayed shifts
- Transmission slipping or overheating
- Vehicle enters limp mode
2. Most Common Causes
- Faulty or damaged transmission fluid pressure sensor 'D'
- Short circuit to voltage in the sensor signal circuit wiring
- Loose, corroded, or poor ground electrical connection
- Incorrect transmission fluid level or degraded fluid
- Internal failure in the transmission control module (TCM)
- Internal mechanical transmission problem causing actual excessive pressure
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the sensor and wiring for damage, corrosion, or loose connections.
Step 3: Use a multimeter to check sensor signal voltage (should be 0.5-4.5V at idle) and compare to manufacturer specs.
Step 4: Test the sensor by applying vacuum or pressure and monitoring voltage changes.
Step 5: If wiring and sensor are good, check transmission fluid level and condition; perform a pressure test if needed.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can cause transmission damage. You may experience harsh shifting or limp mode, which reduces safety.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Replacing the sensor can range from $100-$300 including parts and labor, depending on vehicle make and model.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.