The Check Engine Light may illuminate with a fault code P1121 stored. It is commonly caused by a failed three way coolant control valve. Valve replacement is recommended if this occurs.

Some Mitsubishi Diamante owners report experiencing cruise control malfunctions after removing a drive line obstruction, often linked to issues with the control module, sensor, or switch. These problems may stem from failed components that prevent the cruise control system from engaging or holding speed, despite power being available to the dash and fuse. Additionally, throttle actuation issues, such as a faulty throttle position sensor, can lead to the engine's computer overcompensating with fuel, which may result in black exhaust from the tailpipe. Owners are advised to thoroughly troubleshoot the cruise control system and inspect key components like the control module, sensor, and throttle to identify any damage or malfunction caused during the obstruction removal process.