What Does P0878 Mean?
The TCM has detected that the signal voltage from transmission fluid pressure sensor/switch 'D' is above the maximum expected threshold. The elevated signal prevents the TCM from properly monitoring hydraulic pressure in circuit 'D', which can result in incorrect shift pressure commands and harsh shift quality.
Common Causes
30%
Open ground circuit for sensor 'D'
28%
Failed pressure sensor 'D' with open internal element
22%
Signal wire shorted to battery voltage or reference voltage
12%
Disconnected or unseated sensor connector
8%
TCM internal pull-up fault
Diagnostic Steps
1
Measure the signal voltage at the sensor 'D' connector — if near 5V or battery voltage, the circuit is being pulled high.
2
Verify good ground continuity from the sensor ground pin to TCM ground (should be less than 0.5 ohms).
3
Disconnect sensor 'D' and check if signal drops; a persistent high signal with sensor disconnected indicates a wiring short.
4
Inspect the harness for damage where it routes near hot exhaust or sharp transmission case edges.
5
Replace pressure sensor 'D' if wiring and grounds test normal; verify signal returns to proper operating range.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The TCM has detected that the signal voltage from transmission fluid pressure sensor/switch 'D' is above the maximum expected threshold. The elevated signal prevents the TCM from properly monitoring hydraulic pressure in circuit 'D', which can result in incorrect shift pressure commands and harsh sh...
The most common cause of P0878 (Transmission Fluid Pressure Sensor/Switch "D" Circuit High) is: Open ground circuit for sensor 'D'
Typical repair costs for P0878 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Expect harsh or unpredictable shifts. The transmission may enter limp mode. Limit driving to necessary trips and have the vehicle serviced soon.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0878 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission Hydraulic Pressure Monitoring
Difficulty
Type
Generic (SAE)
Recommended Tools
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