Diagnostic article Generic OBD-II
P0778: Solenoid B feedback current fails to follow its target
P0778 evaluates accumulated current-tracking error in the documented SLC1 transmission-solenoid circuit.
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Documented application
2009 General Motors diagnostic parameter file 09OBDG04 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.
The P0778 row in GM's group 04 transmission summary is associated with the solenoid identified as SLC1. The controller compares target current with feedback current and adds the difference over successive evaluations. This is an electrical feedback monitor, even though the generic code name uses pressure-control solenoid B.
The accumulation has reset conditions
Error is accumulated every ten milliseconds. The source resets the accumulated result when the detection window becomes invalid, current error returns near zero or its direction reverses. Consequently, an isolated mismatch does not necessarily have the same significance as persistent error of one sign.
Emergency mode must be inactive, the diagnostic state must be enabled and specified companion current-circuit codes must be absent. These requirements help explain why a monitor may remain incomplete while another electrical fault is active.
Confirm the channel mapping before testing
The source's SLC1 label and the generic solenoid-B name require the correct transmission documentation to identify the physical circuit. They do not provide a universal location or connector pin.
Record target and feedback current where available, together with the qualifying state and related faults. The summary does not prove a hydraulic pressure defect or a particular failed component. After correction, verify sustained current tracking and completed electrical monitoring. A smoother shift or a code that has merely been cleared cannot substitute for that evidence.
Source and applicability
2009 General Motors diagnostic parameter file 09OBDG04 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.
GM diagnostic parameters, PDF page 4 · GM diagnostic parameters, PDF page 5.
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
Pressure Control Solenoid B Electrical
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