P2121: pedal channel one has a separate rationality classification

P2121 is an accelerator-position channel-one rationality diagnostic in this GM 2009 table. Its purpose is not merely to duplicate the ordinary low- and high-circuit codes. The source describes a monitoring path that detects an out-of-range signal when the main-processor classification cannot resolve the minimum or maximum fault.

The companion-code state matters

The row lists the channel-one signal outside its encoded 10–93 percent range and excludes P2122/P2123 when set, pending or confirmed. The table gives a 100-millisecond evaluation and describes monitoring across the listed engine and ignition states.

Those percentages belong to the signal representation in this document. They are not instructions to press the accelerator to a particular physical travel percentage or a universal specification for every pedal assembly.

Preserve the reason for the distinct code

Record the exact channel, relevant low/high circuit codes and available controller context. If a conventional range fault is also present, its state matters to interpreting the rationality record. A single driver complaint about poor throttle response cannot establish this specific electronic classification.

The abbreviated reference to a main-processor problem does not by itself prove that the engine controller hardware must be replaced. The source gives no component-isolation procedure or wiring pinout. A technician needs the appropriate vehicle diagnostics to distinguish the signal path and controller evaluation involved. Verification should demonstrate the relevant qualified test, rather than treating a cleared code as proof of a repaired pedal.

Source and applicability

GM 2009 09OBDG06 Engine Diagnostics, cited accelerator-position channel-one rationality monitor only. Individual vehicle, engine, wiring and calibration applicability has not been established from this parameter file.

General Motors source, physical page 20