P0748: Pressure-solenoid current error accumulates over time

In GM's group 04 transmission summary, P0748 belongs to pressure solenoid SLT. Its electrical monitor compares requested current with measured feedback current and accumulates the difference. The result is more specific than a general complaint of harsh shifting.

Persistent error differs from a brief deviation

The controller adds current error every ten milliseconds. The accumulated value is cleared when the detection window closes, the error returns within a small band or the error changes sign. A brief deviation that recovers can therefore be treated differently from a sustained mismatch in the same direction.

The check requires suitable ignition voltage, an active diagnostic state and no emergency mode. Related low- and high-current circuit faults must not already be active. Those prerequisites matter when assessing why the monitor did not complete.

Electrical feedback is not a pressure measurement

The code does not directly measure hydraulic line pressure or identify a particular internal transmission defect. It establishes disagreement in a monitored solenoid-current path. A shift-quality symptom may be relevant, but it cannot replace that electrical evidence.

Preserve the solenoid identity, requested current, feedback current and companion circuit codes. Use the exact transmission's diagnostic procedure to separate the possible electrical causes. Verification should show stable current tracking and a completed monitor, rather than only a subjective improvement in shifting or an empty code list after clearing.

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 3 · GM diagnostic parameters, PDF page 4.