Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
2003 Hummer H2 V8-6.0LFACTORY OEM SERVICE PROCEDURE
Throttle Actuator Control (TAC) System
POWERTRAIN CONTROL MODULE
The PCM determines the driver's intent and then calculates the appropriate throttle response. This information is sent to the TAC module through a dedicated serial data line.
MODES OF OPERATION
Normal Mode
During the operation of the TAC system, several modes or functions are considered normal. The following modes may be entered during normal operation:
- Minimum pedal value-At key-up the PCM updates the learned minimum pedal value.
- Minimum TP values-At key-up the PCM updates the learned minimum TP value. In order to learn the minimum TP value, the throttle blade is moved to the closed position.
- Ice break mode-If the throttle is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the control module commands the maximum pulse width several times to the throttle actuator motor in the closing direction.
- Battery saver mode-After a predetermined time without engine RPM, the control module commands the battery saver mode. During the battery saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used to maintain the idle position and allows the throttle to return to the spring loaded default position.
Reduced Engine Power Mode
When the PCM detects a condition with the TAC system the PCM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
- Acceleration limiting - The control module will continue to use the accelerator pedal for throttle control; however, the vehicle acceleration is limited.
- Limited throttle mode - The control module will continue to use the accelerator pedal for throttle control; however, the maximum throttle opening is limited.
- Throttle default mode - The control module will turn off the throttle actuator motor and the throttle will return to the spring loaded default position.
- Forced idle mode - The control module will perform the following actions:
- Limit engine speed to idle by positioning throttle position, or by controlling fuel and spark if throttle is turned off.
- Ignore accelerator pedal input.
- Engine shutdown mode - The control module will disable fuel and de-energize the throttle actuator.
The PCM determines the driver's intent and then calculates the appropriate throttle response. This information is sent to the TAC module through a dedicated serial data line.
MODES OF OPERATION
Normal Mode
During the operation of the TAC system, several modes or functions are considered normal. The following modes may be entered during normal operation:
- Minimum pedal value-At key-up the PCM updates the learned minimum pedal value.
- Minimum TP values-At key-up the PCM updates the learned minimum TP value. In order to learn the minimum TP value, the throttle blade is moved to the closed position.
- Ice break mode-If the throttle is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the control module commands the maximum pulse width several times to the throttle actuator motor in the closing direction.
- Battery saver mode-After a predetermined time without engine RPM, the control module commands the battery saver mode. During the battery saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used to maintain the idle position and allows the throttle to return to the spring loaded default position.
Reduced Engine Power Mode
When the PCM detects a condition with the TAC system the PCM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
- Acceleration limiting - The control module will continue to use the accelerator pedal for throttle control; however, the vehicle acceleration is limited.
- Limited throttle mode - The control module will continue to use the accelerator pedal for throttle control; however, the maximum throttle opening is limited.
- Throttle default mode - The control module will turn off the throttle actuator motor and the throttle will return to the spring loaded default position.
- Forced idle mode - The control module will perform the following actions:
- Limit engine speed to idle by positioning throttle position, or by controlling fuel and spark if throttle is turned off.
- Ignore accelerator pedal input.
- Engine shutdown mode - The control module will disable fuel and de-energize the throttle actuator.
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.