Diagnostic article Generic OBD-II
P0600: Internal transmission-controller serial communication faults
Read the GM P0600 internal SPI monitor and distinguish its steady-state and shifting criteria from external vehicle-network communication loss.
Read before applying this article
Documented application
2025 GM 25OBDG06C, 25OBDG06B documented monitor only. Vehicle, engine and calibration applicability must be confirmed from the matching service information; no model fitment is inferred.
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.
P0600 is generically called serial communication link. In the cited GM transmission-controller implementation, it concerns an internal SPI link between the microprocessor and the solenoid-control integrated circuits. This scope is crucial: the monitor is not simply reporting that an external CAN module stopped responding.
Internal status changes have two timing limits
The controller reads SPI range-check status to identify devices commanded outside a valid calibration range. It also reads SPI bus status to evaluate the validity of data and devices. A static bit in an SPI message remaining in the wrong state qualifies after at least one second during steady operation or at least 100 milliseconds during a shift.
The diagnostic checks every 20 milliseconds and uses one-trip behavior. Sampling frequency, steady-state duration, and shift duration are separate quantities. Treating the 20-millisecond execution interval as the failure threshold would misread the table.
Establish the operating and supply context
The normal battery-voltage window is 9–18 volts. During engine cranking, the listed qualifications also require crank time below four seconds and battery voltage above 10 volts. Preserve whether the event occurred while shifting, in steady operation, or around a supply disturbance.
Record the transmission controller's internal failure detail and associated solenoid or supply faults before interpreting a generic communication scan. The code alone does not select an external data-bus wire for repair and does not establish that a particular solenoid is mechanically stuck. Internal SPI evidence requires the matching controller diagnostic procedure; these summary rows do not authorize a module replacement or a universal repair for every vehicle using P0600.
Source and applicability
2025 GM 25OBDG06C, 25OBDG06B documented monitor only. Vehicle, engine and calibration applicability must be confirmed from the matching service information; no model fitment is inferred. These criteria explain controller logic, not a complete repair procedure. 25OBDG06C, PDF page 1311. 25OBDG06B, PDF page 789.
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
Serial Communication Link
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