Diagnostic article Generic OBD-II
P0638: bank-1 throttle duty-cycle demand exceeds its limit
P0638 checks the magnitude of bank-1 throttle-actuator duty cycle in this calibration.
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Documented application
2025 GM 25OBDG07A Part2 diagnostic monitor documentation; the application-matrix filename mismatch is unresolved, so no model or engine applicability is inferred.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P0638 checks the magnitude of bank-1 throttle-actuator duty cycle in this calibration. The failure threshold changes with measured battery voltage, so it is not simply a fixed throttle-position error.
Voltage compensation changes the boundary
The threshold is the smaller of 95 percent and 80 percent multiplied by 13.5 volts divided by measured battery voltage. The table gives a 0.6001-second interval and one-trip reporting. For illustration, at 13.5 volts the formula yields an 80-percent boundary; that arithmetic is an explanation of the published formula, not a vehicle test result.
The power stage must be on, actual position valid, adaptation release inactive, and the controller in drive or post-drive state. The desired-position gradient is also constrained, separating this check from unrestricted rapid command changes.
What a high duty result means
The monitor reports that control effort exceeded its calibrated range in an eligible state. It does not directly establish why that effort was required or prove the actuator is mechanically stuck.
Verification should compare duty magnitude with the voltage-adjusted threshold while confirming the enable conditions and monitor completion. A normal throttle angle alone can coexist with excessive control effort. Use the vehicle’s procedure to establish the cause before selecting a throttle-body or electrical repair.
Documentation and applicability
These details describe the monitor in GM’s 2025 25OBDG07A Part2 file. Its application-matrix filename does not match the download index, so model and engine applicability remain unresolved. Use the vehicle’s correct service information before applying these calibration details.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Throttle Actuator Control Range/Performance Bank 1
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT