Diagnostic article Generic OBD-II
P2688: fuel-filter heater feedback indicates the short-to-ground branch
The GM P2688 monitor evaluates low fuel-heater driver feedback during its off state and distinguishes it from other circuit failures.
Read before applying this article
Documented application
GM 2015 15OBDG04 fuel-filter heater driver monitor. Only the cited monitor and calibration are described; per-code vehicle and engine applicability has not been 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.
P2688 is the fuel-filter heater low-circuit diagnosis in this GM table. It describes the low-side driver's short-to-ground branch. The relevant event is low feedback while the driver is commanded off, not simply a low fuel-temperature reading.
Keep the fault category with the measurement
The source's open-circuit branch, P2687, also refers to low feedback during an off command. Their different electrical fault classifications show why a technician needs the complete circuit procedure rather than a single voltage observation. An open load path and a path held to ground require different confirmation even when a simplified scan display looks similar.
The table provides source-specific impedance criteria, but it does not identify a universal connector location or permit testing through an energized fuel-system circuit without the required precautions.
Check whether the diagnostic was enabled
The monitor requires battery voltage above its operating threshold for the stated time and engine speed above a calibration-dependent limit. It also excludes the specified post-drive condition. A two-second failure duration and a 0.2-second evaluation rate apply when these prerequisites are met.
A useful work record includes heater command, driver fault status, supply history and relevant engine state. The code does not by itself condemn the heater element or controller. Repair verification should demonstrate correct circuit behavior in the eligible state and address any associated faults; a temporary absence after memory clearing is not proof that the short-to-ground condition was found.
Source and applicability
GM 2015 15OBDG04 fuel-filter heater driver monitor. Only the cited monitor and calibration are described; per-code vehicle and engine applicability has not been established.
15OBDG04 Engine Diagnostics, physical PDF page 254.
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
Fuel Supply Heater Control Circuit 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