Diagnostic article Generic OBD-II
P0878: Pressure sensor D high is an electrical limit, not a pressure verdict
P0878 evaluates the limited-slip-differential pressure sensor above 4.530 volts in this GM example, with disputed supply eligibility.
Read before applying this article
Documented application
2025 GM 25OBDG07A Part 2, specific documented monitor only. Vehicle, engine and calibration applicability require confirmation; application-matrix filename join is unresolved.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P0878 is the high-circuit code for pressure sensor D. The cited GM TCM implementation assigns it to the limited-slip-differential pressure input. Its primary criterion is electrical, so the code cannot be read as proof that the differential’s actual pressure is excessive.
The high input has a persistence requirement
The table lists voltage above 4.530 volts, 30 millivolts of hysteresis and at least 150 milliseconds of confirmation. Cranking and STOP state are excluded, and the main battery supply must be within the documented 8.75–18-volt eligible interval.
Its VREF1 enable window is printed inconsistently, requiring both above 5.5 and below 4.5 volts. The original PDF contains those bounds. Their intended correction must come from applicable service information, not an editorial guess.
Preserve channel and reference-fault context
P0882/P0883 and P0642/P0643 disable the monitor. A non-returning P0878 while one of those faults remains active cannot establish that the D-channel input has passed.
Keep the actual pressure-sensor voltage and reference-rail status together. A main system-pressure measurement from another sensor is not verification of this limited-slip-differential channel. The summary provides no connector location or component replacement instruction. Resolve the reference-window ambiguity and follow the matching circuit procedure to determine whether the sensor, wiring or input electronics produced the high report.
Source and applicability
This explanation covers the cited GM monitor, not every vehicle carrying this code. The application-matrix filename does not resolve cleanly to this file, so no model or engine fitment is assigned. GM diagnostic table, PDF page 907.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Transmission Fluid Pressure Sensor/Switch D Circuit High
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT