What does the P0685 fault code mean when the car won't start?

[Duncan]

P0685 indicates an Engine Control Module (ECM) malfunction, which could be caused by engine issues or related circuit problems. The Engine Control Module (ECM) continuously monitors and controls the normal operation of the engine. Here's relevant information: ECM: The Automotive Engine Control Module (ECM) is one of the most crucial automotive electronics. Early ECMs required three printed circuit boards, composed of 12 LSIs and dozens of SSIs. Today's ECMs use microcontroller-based VLSI technology and require only one printed circuit board. Composition: The core component of ECM is a microprocessor-based VLSI microcontroller, which collects control parameters from various sensors (temperature, pressure, gas-sensitive, displacement) to implement automatic control over engine operation, fuel injection, ignition, combustion, operation, and emissions. The ECM also connects to the vehicle's main computer via a bus system.