Diagnostic article Generic OBD-II
P2686: Supply C high is checked after HSO7 is switched off
P2686 detects an output that remains too high during the transmission shutdown test, with delayed reporting from stored memory.
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Documented application
2025 GM 25OBDG07A Part 2 documented monitor only; its application-matrix filename join is unresolved. No model, engine or universal calibration applicability 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.
The P2686 implementation documented here concerns high-side output seven. During shutdown, the controller disables HSO7 and checks whether its voltage falls to the expected state. Remaining above 70% of battery voltage for at least 60 ms produces the listed shorted-switch finding.
Startup reporting can describe an earlier event
The fault is stored at powerdown and read on the next startup. This makes the shutdown sequence the relevant event to preserve, even if the first visible indication arrives after the vehicle wakes again. A voltage recorded only during normal powered operation does not evaluate the same condition.
Battery change during the test must stay below 1.5 V, and the source disables this check when P0882 or P0883 is present. A disrupted supply can therefore prevent a valid follow-up test.
Keep the failure classes separate
The neighboring P2684 open-load monitor uses a different threshold and a low-side load-path test. Do not combine those criteria into a single generic supply fault. Confirm HSO7’s exact assignment and the stored shutdown result through applicable service data. The summary supports the off-state high classification but does not independently identify the failed switch or external circuit element.
Document scope and source
2025 GM 25OBDG07A Part 2 documented monitor only; its application-matrix filename join is unresolved. No model, engine or universal calibration applicability is inferred. These figures explain the cited controller logic, not a vehicle-specific repair instruction. Match the vehicle’s service information before applying them.
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
Actuator Supply Voltage C Circuit 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