Detectable Lines and Non-Detectable Lines

In some wiring diagrams, two kinds of lines with different thicknesses are used to represent wires.

^ A line with regular thickness (wider line) represents a "detectable line for DTC (Diagnostic Trouble Code)". A "detectable line for DTC" is a circuit in which ECM (ECCS control module) can detect malfunctions with the on-board diagnostic system.
^ A line with less thickness (thinner line) represents a "non-detectable line for DTC". A "non-detectable line for DTC" is a circuit in which ECM cannot detect malfunctions with the on-board diagnostic system.