P0828: manual-shift input exceeds its normalized high limit

P0828 is the high-circuit result for the manual up/down shift input in the cited GM MGG table. The signal is expressed as switch voltage divided by ignition voltage. The high boundary is therefore a ratio, not a universal terminal voltage.

Keep high input separate from a held request

This code concerns a reading above the allowed electrical band. The same document uses P085F for a switch that remains in an otherwise recognized range. A persistent shift request and an out-of-range high signal require different interpretations.

The monitor's high threshold is 25.5 percent of ignition voltage for the documented implementation. A technician should use the actual supply and correct circuit information before translating that controller-level threshold into a physical measurement.

Qualify the absence of a repeat fault

The table requires the high condition to persist for 30 seconds, with valid engine-speed information and qualified voltage. It also excludes specified bus and ignition-supply faults. Clearing memory and performing a short stationary check may leave the relevant monitor unevaluated.

GM lists this as a special non-MIL result. An engine warning lamp that stays off does not demonstrate that the input passed.

Preserve the exact high-code result, normalized input behavior and any supply or communication findings. The summary identifies an input-circuit concern but cannot choose among selector, connection or controller causes without the applicable service diagnosis.

Application limits

2015 GM 15OBDG06 TCM MGG unique section. No vehicle model, switch location or universal voltage specification is inferred.

Source

15OBDG06 Transmission Diagnostics, physical PDF pages 83.