Diagnostic article Generic OBD-II
P0827: manual-shift input is low relative to ignition voltage
The GM MGG P0827 monitor uses a normalized switch-voltage ratio with a sustained low condition.
Read before applying this article
Documented application
2015 GM 15OBDG06 transmission summary, MGG unique section. Thresholds and enable conditions are document-specific; vehicle fitment is not established.
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.
P0827 in the cited GM MGG transmission table means the manual up/down shift-switch signal is too low. The controller evaluates switch voltage as a percentage of ignition voltage, not as one fixed standalone voltage.
Supply context changes the interpretation
Because the denominator is ignition voltage, a reading should be interpreted with the corresponding supply value. Comparing the switch signal with a voltage remembered from another vehicle or another supply condition can give the wrong conclusion.
The documented low boundary is five percent of ignition voltage. This is the controller's normalized criterion; the correct physical test still requires the vehicle wiring diagram and measurement conditions.
The monitor needs a sustained valid operating state
The table requires a 30-second low condition and qualifies battery voltage, engine speed and the validity of engine-speed communication. It excludes specified CAN and ignition-supply faults. A brief key-on measurement or a test during network disruption is not equivalent to the complete monitor.
The result is listed as a special diagnostic without MIL illumination. A transmission mode-input problem can therefore be present without an engine warning lamp.
Record the manual-switch signal, ignition supply and communication status together. These observations help separate an electrical input problem from a complaint about the transmission failing to execute a shift. The code does not by itself prove an internal gearbox fault or identify a replacement selector assembly.
Application limits
2015 GM 15OBDG06 transmission summary, MGG unique section. Thresholds and enable conditions are document-specific; vehicle fitment is not established.
Source
15OBDG06 Transmission Diagnostics, physical PDF pages 83.
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
Up and Down Shift Switch Circuit Low
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