P26B8: coolant bypass valve C driver reports a ground short

P26B8 is the low control-circuit diagnosis for coolant bypass valve C. The source describes a short to ground in the energized H-bridge supply/load circuitry and separates opening from closing motor direction.

Direction affects qualification

The opening branch requires an opening command and no corresponding ground-short fault in the closing direction. The closing branch reverses those conditions. Both require valid run/crank, no engine cranking, enabled diagnostics and a determinate driver-low status. This makes direction and driver feedback useful evidence, not just whether the valve moved.

The table prints “999.9 seconds out of a 0 seconds window” for both branches. That is not a usable fault-setting duration. This article retains the supported electrical strategy and Type B, two-trip classification while leaving actual timing unresolved.

Diagnostic interpretation

Preserve which movement direction was commanded when the shorted-low report appeared. A fault observed during one direction should not automatically be assumed to have been tested under the other branch. Use the exact service procedure to assess the circuit; the summary provides no external voltage threshold.

Verification should establish a completed applicable driver check after correction. A position response alone does not prove the electrical report is resolved, and the malformed timing cell must not be used to claim that the monitor is intentionally disabled.

Source and application limits

This explanation covers the cited 2025 GM monitor. Confirm the vehicle and calibration in its service information before applying these limits; inclusion in this file does not establish model compatibility. GM diagnostic parameters, PDF page 845.