DTC P0612: Fuel Injection Control Module Internal Fault: Description
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The Engine Control Module (ECM) monitors the condition of the ignition relay control circuit. If the ECM senses excessive voltage on this circuit, DTC P0612 will set.