P0593: cruise switch B input in the short-to-power band

The documented P0593 monitor classifies cruise-control circuit B as shorted toward power when its analog-to-digital count ratio is in the 1.005–1.035 band. The fault concerns the switch input, not vehicle speed or throttle response.

The input scale is essential

Those numbers are ratios, not volts. A diagnostic check that treats 1.035 as a universal voltage threshold would apply the wrong units. The condition must occupy two seconds within a 25-second period while the relevant diagnostic is enabled.

The BCM reports the high input to the ECM. Once it fails, the ECM disables and disengages cruise for the rest of the current key cycle regardless of a later passing input. This explains why a recovered signal and unavailable cruise can coexist without proving a second failure.

Confirm the electrical state

Record whether the ratio remained in the high band long enough and whether it later returned to a recognized switch state. Those observations separate a persistent fault from an intermittent event whose functional consequence remains latched.

Verification should assess the correct analog input and reporting path through the applicable service procedure. The source lists Type B reporting over two trips but does not identify a specific switch, connection or control-module failure. It provides no authorization to bypass driver controls or perform hazardous probing around restraint-related steering-wheel components.

Source and applicability

2025 GM 25OBDG04B diagnostic parameter tables; the cited monitor only. Vehicle, engine and calibration applicability must be confirmed separately. These tables describe detection logic, not a complete repair procedure or a component replacement verdict. gm-2025-04b, PDF page 568.