Diagnostic article Generic OBD-II
P0787: Timing solenoid feedback stays low when commanded on
P0787 detects low timing-solenoid circuit feedback despite an on command in this GM transmission example.
Read before applying this article
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.
In GM's GMDAT transmission summary, P0787 identifies a ground-short condition in the timing-solenoid circuit. The meaningful relationship is between command and feedback: the controller commands the monitored channel on, but the observed voltage corresponds to the off state.
Command state changes the interpretation
A low signal when a channel is intentionally off would not establish this documented fault. The source specifically associates the low feedback with an on command. Preserve both pieces of information rather than reporting only that a terminal measured zero volts.
The monitor waits after a shift-solenoid output change and requires the relevant diagnostic state. Emergency mode must be inactive. Its failure logic counts three events, each with a sustained half-second condition, rather than condemning the circuit from one instantaneous transition.
Keep it separate from the opposite feedback direction
The adjacent P0788 row checks high or open-circuit feedback under an off command. Those are distinct electrical observations. The code alone does not identify whether the problem lies in the solenoid, wiring or control electronics.
Confirm the exact timing-solenoid circuit through vehicle-specific service information before testing. Verification should show that feedback follows the intended command and that the electrical monitor completes. An apparently normal gear change or an erased code does not establish that the monitored circuit remains correct through its required state changes.
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 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