The programmable read-only memory (PROM) chip in each ECU is not replaceable. Technician B says the PROM chip is the only serviceable part in the ECU. Who is correct?

The programmable read-only memory (PROM) chip in each ECU is not replaceable. Technician B says the PROM chip is the only serviceable part in the ECU. Who is correct?

• A. Technician A
• B. Technician B
• C. Both Technician A and Technician B
• D. Neither Technician A nor Technician B

Answer: (B)

In ECU service, the part you actually address to alter how the unit behaves is the memory that stores its firmware and calibration—the PROM. This memory defines the engine control logic, so updating or swapping the PROM data is the targeted way to service the ECU’s performance. The rest of the circuitry inside the ECU is typically not field-serviceable; modules are usually replaced rather than repaired in detail. Because the practical, actionable service in many cases centers on the PROM, the technician who says this memory is the only serviceable part is the best fit. Other internal components aren’t realistically serviced in routine maintenance, so focusing on the PROM aligns with common ECU servicing practices.