Diagnostic article Generic OBD-II
P0788: Timing-solenoid circuit stays high under an off command
P0788 detects high or open timing-solenoid circuit feedback when the controller requests the off state.
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Documented application
2009 General Motors diagnostic parameter file 09OBDG01 GMDAT TRANS Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability 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.
P0788 checks the timing-solenoid electrical circuit in GM's GMDAT transmission summary. The table describes a high or open condition when the controller commands the monitored signal off but observes the on-state voltage instead.
An open circuit can share the high classification
The word high does not prove that a wire is directly shorted to supply. The source explicitly includes an open circuit in this classification. The vehicle's actual driver and feedback arrangement determines how those faults appear, so the matching circuit procedure is essential.
The monitor waits after a solenoid-output change, requires its diagnostic state to be active and excludes emergency mode. It then counts three sustained failure events, each lasting half a second. These qualifications distinguish a repeated electrical disagreement from a normal switching transition.
Preserve the off-command evidence
A useful record identifies the requested state and observed feedback at the failure. A high voltage without that command context cannot reproduce the diagnostic conclusion. The neighboring P0787 row concerns the opposite relationship: low feedback under an on command.
The summary does not identify a failed solenoid versus wiring or control electronics solely from P0788. After the prescribed diagnosis and correction, verify that feedback follows both relevant commanded states and that monitoring completes. A normal shift on one occasion or a cleared fault list does not establish that the original electrical disagreement is gone.
Source and applicability
2009 General Motors diagnostic parameter file 09OBDG01 GMDAT TRANS Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established. This explanation describes the documented monitor, not a universal repair procedure.
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
Shift Timing Solenoid A 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