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 within the transmission to ensure proper shift timing and line pressure. A high circuit condition typically points to a short to voltage, a faulty sensor, or internal transmission issues. This can lead to harsh shifts, slipping, or transmission overheating.
01. Most Common Causes
- Faulty transmission fluid pressure sensor
- Short to voltage in the sensor circuit
- Damaged wiring or connector
- Internal transmission problem (e.g., clogged fluid passages)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or erratic shifting
- Transmission slipping or overheating
- Reduced fuel economy
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Inspect the transmission fluid level and condition; top off or replace if necessary.
Step 3: Visually check the sensor wiring and connector for damage, corrosion, or loose connections.
Step 4: Using a multimeter, test the sensor signal voltage at the PCM connector; compare to manufacturer specs.
Step 5: If voltage is high with sensor disconnected, repair short to voltage in the harness; if voltage normal, replace the sensor.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with a high circuit condition can cause transmission damage due to incorrect pressure regulation, leading to costly repairs.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for a sensor replacement, but can be higher if wiring repairs or internal transmission work is needed.