Toyota Sienna ECM replacement issue with recurring codes P500, C1201, P456, and P0606 after 35 miles on Toyota Sienna

Some Toyota Sienna owners report experiencing recurring diagnostic trouble codes (DTCs) such as P500, C1201, P456, and P0606 even after replacing the Engine Control Module (ECM). These codes suggest that the ECM replacement may not have resolved the underlying issues effectively. Specifically, the P500 code often relates to vehicle speed sensor problems, while C1201 indicates a malfunction within the Engine Control System, potentially linked to the ECM. Additionally, the P456 code points to evaporative emission control system leaks that could be affecting the ECM, and P0606 highlights an ECM/PCM Processor Malfunction, which may stem from sensor or circuit issues rather than the ECM itself. Owners are advised to conduct thorough diagnostics to identify the root causes, including checking the vehicle speed sensor and related systems. Seeking assistance from a qualified mechanic or dealership experienced in ECM-related issues is crucial for accurate troubleshooting, as electrical glitches and faulty ECM signals can lead to performance problems and erratic transmission behavior.