In the Allison ATEC/CEC transmissions, which device replaces the modulator valve used in hydraulically controlled transmissions?

In the Allison ATEC/CEC transmissions, which device replaces the modulator valve used in hydraulically controlled transmissions?

• A. The transmission oil pressure control valve
• B. The throttle position sensor
• C. The transmission temperature sensor
• D. The vehicle speed sensor

Answer: (B)

In electronically controlled Allison transmissions, the shift points are determined by the transmission control module using signals from sensors that measure engine load, rather than by a vacuum-operated modulator valve. The throttle position sensor provides the ECU with the amount of throttle opening, i.e., engine load, and the ECU uses that information to decide when to upshift or downshift. This replaces the old hydraulically controlled modulator valve, which used engine vacuum to influence hydraulic shift pressure. The other sensors shown (oil pressure, temperature, vehicle speed) contribute to protection and refinement of shift logic but do not directly substitute for the modulator valve’s role.

In electronically controlled Allison transmissions, the shift points are determined by the transmission control module using signals from sensors that measure engine load, rather than by a vacuum-operated modulator valve. The throttle position sensor provides the ECU with the amount of throttle opening, i.e., engine load, and the ECU uses that information to decide when to upshift or downshift. This replaces the old hydraulically controlled modulator valve, which used engine vacuum to influence hydraulic shift pressure.

The other sensors shown (oil pressure, temperature, vehicle speed) contribute to protection and refinement of shift logic but do not directly substitute for the modulator valve’s role.