P0261: Cylinder 1 injector low-side circuit checked in the off state

P0261 is the cylinder 1 injector circuit-low code. The cited GM direct-injection monitor interprets it as short-to-ground behavior on the low-side driver. It checks voltage feedback with the output powered off.

Low feedback must be paired with command state

The controller-specific specification is at or below one volt between signal and controller ground during the relevant test. That does not make every low injector-control voltage a fault: an intentionally driven output has a different meaning. The off-state condition is central to this diagnosis.

The test requires battery voltage of at least 11 volts and acceptable P062B injector-control status. It counts ten failures among twenty samples, with 100 milliseconds between samples, and uses Type A, one-trip reporting.

What the code does and does not isolate

This row identifies the cylinder 1 electrical path, not a measured fuel-flow shortfall. It cannot establish spray quality, injector clogging or the physical point where the circuit is pulled low. Confirm cylinder numbering and the applicable driver architecture before choosing a test location.

Preserve the driver command, related fault statuses and available feedback. Use the approved direct-injection circuit procedure to separate harness, connection, injector and controller possibilities. Verification should demonstrate that the off-state low-feedback monitor completes without failure. A smooth idle alone does not show that this electrical test passed, and improvised powered probing is inappropriate for the injection driver.

Source and applicability

This explanation is limited to the 2025 GM 25OBDG03A monitor on page 226. Its thresholds are calibration examples, not universal specifications. Confirm the vehicle, engine and controller procedure before applying them.