Detroit Diesel Code
The DDEC diagnostic systems uses two types of diagnostic trouble codes. Active codes are conditions that are presently occurring. Inactive codes are faults that have occurred previously.
On the DDEC IV system, active codes will flash on the Stop Engine Lamp (SEL) in numerical order when the diagnostic request switch is held. If there are no codes, code 25 will flash. Inactive codes will flash on the Check Engine Lamp (CEL) in most recent to least recent order when the diagnostic request switch is held. If there are no codes, code 25 will flash.
On the DDEC VI system, active codes will flash on the Red Stop Lamp in numerical order when the diagnostic request switch is held. Inactive codes flash on the Amber Warning Lamp (AWL). Flashing codes provide a four-digit number,