Which part of the transmission ECU is described as the only serviceable component?

• A. Shift lever
• B. Throttle position sensor
• C. PROM chip
• D. Hall effect switches

Answer: (C)

The key idea is that, in many transmission ECUs, the only part designed to be serviced is the memory element that holds the control firmware. This memory is the PROM chip, and it carries the program and calibration data that determine shift points, line pressure, and other essential timing decisions for the transmission. Because the firmware defines how the transmission behaves, swapping or updating this PROM chip can refresh the control logic, whereas the rest of the ECU’s hardware tends to be sealed or not intended for individual replacement.

The shift lever is just a mechanical input that tells the system when you want to change gears. The throttle position sensor is a separate sensor that provides engine throttle data to the ECU, not part of the ECU’s internal control memory. Hall effect switches are sensors used to detect rotational or positional changes, again external to the ECU’s programmable logic. Since those items are not the programmable logic inside the ECU, the PROM chip stands out as the component designed for service or replacement.