P0D26: Charger precharge fails to reach and hold its voltage window

Reaching the target is only part of the test

P0D26 in GM’s documented charging system means precharge did not satisfy its completion criteria within ten seconds. The target is the battery pack’s voltage, with an allowed percentage difference. This is not a fixed charger-bus voltage that can be applied to every state of charge.

A passing result requires the absolute percentage deviation between charger-bus voltage and pack voltage to remain below 5% continuously for at least 0.25 second. That stable interval must occur before the ten-second precharge deadline. Briefly touching the target and then falling away therefore differs from a completed pass.

Conditions that make the result meaningful

The table requires system voltage above 9 volts, the multipurpose contactor open and the charger contactor in precharge. A comparison recorded after the circuit has moved into another state cannot fully explain this monitor. The useful evidence is a time sequence showing both voltages, their relative difference and the contactor-state transitions.

Two patterns lead to different diagnostic questions: a bus that never approaches pack voltage, and a bus that approaches it but does not remain within the required window. That distinction follows from the published pass logic; the summary does not provide a confirmed component cause for either pattern.

This source must not be used as a manual precharge procedure. The ten-second diagnostic deadline and quarter-second stability requirement are not safe-discharge or isolation times. Matching service information and qualified high-voltage diagnosis are needed before testing the charging power circuit or condemning a contactor, resistor or charger.

Source and applicability

15OBDG01 Hybrid Diagnostics, cited controller and monitor only. Historical calibration limits are not universal specifications; per-code vehicle, engine and hardware applicability must be verified.

Manufacturer source, physical page 597.