Electronic Throttle Control Module: Description and Operation

Torque-Based Electronic Throttle Control (ETC)

Overview

The torque-based ETC is a hardware and software strategy that delivers an engine output torque (via throttle angle) based on driver demand (pedal position). It uses an electronic throttle body, the powertrain control module (PCM), and an accelerator pedal assembly to control the throttle opening and engine torque.

Torque-based ETC enables aggressive automatic transmission shift schedules (earlier upshifts and later downshifts). This is possible by adjusting the throttle angle to achieve the same wheel torque during shifts, and by calculating this desired torque, the system prevents engine lugging (low RPM and low manifold vacuum) while still delivering the performance and torque requested by the driver. It also enables many fuel economy/emission improvement technologies such as variable camshaft timing (VCT), which delivers same torque during transitions.

Torque-based ETC also results in less intrusive vehicle and engine speed limiting, along with smoother traction control.

Other benefits of torque-based ETC are:

- eliminate cruise control actuators

- eliminate idle air control (IAC) valve

- better airflow range

- packaging (no cable)

- more responsive powertrain at altitude and improved shift quality

The ETC system illuminates a powertrain malfunction indicator (wrench) on the instrument cluster when a concern is present. Concerns are accompanied by diagnostic trouble codes (DTCs) and may also illuminate the malfunction indicator lamp (MIL).

Electronic Throttle Body (ETB)

The ETB has the following characteristics:

- The throttle actuator control (TAC) motor is a DC motor controlled by the PCM (requires 2 wires).

- There are two designs: parallel and in-line. The parallel design has the motor under the bore parallel to the plate shaft. The motor housing is integrated into the main housing. The in-line design has a separate motor housing.

- An internal spring is used in both designs to return the throttle plate to a default position. The default position is typically a throttle angle of 7 to 8 degrees from the hard stop angle.

- The closed throttle plate hard stop is used to prevent the throttle from binding in the bore. This hard stop setting is not adjustable and is set to result in less airflow than the minimum engine airflow required at idle.

- The required idle airflow is provided by the plate angle in the throttle body assembly. This plate angle controls idle, idle quality, and eliminates the need for an IAC valve.

- There is one reference voltage and one signal return circuit between the PCM and the ETB. The reference voltage and the signal return circuits are shared with the reference voltage and signal return circuits used by the accelerator pedal position (APP) sensor. There are also two throttle position (TP) signal circuits for redundancy. The redundant TP signals are required for increased monitoring reasons. The first TP signal (TP1) has a negative slope (increasing angle, decreasing voltage) and the second signal (TP2) has a positive slope (increasing angle, increasing voltage). The TP2 signal reaches a limit of approximately 4.5 volts at approximately 45 degrees of throttle angle.

Accelerator Pedal Position (APP) Sensor

Depending on the application either a 2-track or 3-track APP sensor is used. For additional information on the APP sensor, refer to Engine Control Components Engine Control Components.

Electronic Throttle Control (ETC) System Strategy

The torque-based ETC strategy was developed to improve fuel economy and to accommodate variable camshaft timing (VCT). This is possible by not coupling the throttle angle to the driver pedal position. Uncoupling the throttle angle (produce engine torque) from the pedal position (driver demand) allows the powertrain control strategy to optimize fuel control and transmission shift schedules while delivering the requested wheel torque.

The ETC monitor system is distributed across two processors within the PCM: the main powertrain control processor unit (CPU) and a separate monitoring processor. The primary monitoring function is carried out by the independent plausibility check (IPC) software, which resides on the main processor. It is responsible for determining the driver-demanded torque and comparing it to an estimate of the actual torque delivered. If the generated torque exceeds driver demand by a specified amount, appropriate corrective action is taken.

ETC System With A 3-Track APP Sensor Failure Mode And Effects Management::

a - ETC illuminates or displays a message on the message center immediately; MIL illuminates after 2 driving cycles

ETC System With A 2-Track APP Sensor Failure Mode And Effects Management::

Electronic Throttle Monitor Operation::

a - Monitor execution is continuous. Monitor false detection duration is less than 1 second to register a concern.

APP and TP Sensor Inputs

Accelerator Pedal Position (APP) Sensor Check::

Correlation and range/performance - sensor disagreement between processors internal to the PCM. Monitor execution is continuous. Monitor false detection duration is less than 1 second to register a concern. Refer to Diagnostic Trouble Code (DTC) Charts and Descriptions for additional DTC information.

Throttle Position (TP) Sensor Check::

a - Correlation and range/performance - sensor disagreement between processors internal to the PCM, TP inconsistent with requested throttle plate position. Monitor execution is continuous. Monitor false detection duration is less than 1 second to register a concern. Refer to Diagnostic Trouble Code (DTC) Charts and Descriptions for additional DTC information.

Electronic Throttle Actuator Control (TAC) Output

Electronic TAC Operation Check::

a - Note: For all DTCs, in addition to the MIL, the powertrain malfunction indicator (wrench) is on for the concern that caused the FMEM action. Monitor execution is continuous. Monitor false detection duration is less than 5 seconds to register a concern.