Usage:
The check engine light, on the truck dashboard, can be used to communicate status or operation problems of the electronic control system.
Trucks With Cruise
The dash mounted cruise switches are used to interrogate the ECM for system status. With the cruise switch in the "off" position, hold the set/resume switch in the resume position until "check engine" light begins to flash. The sequence of flashes represents the system diagnostic message. The first sequence of flashes adds up to the first digit of the diagnostic code. After a one second pause, a second sequence of flashes will occur which represents the second digit of the diagnostic code. Any additional diagnostic codes will follow, after a pause, and will be displayed in the same manner.
Trucks Without Cruise
If cruise control switches are not installed or if their configuration (such as a GM type switch) does not permit their usage for checking diagnostic codes, then a push button momentary ON switch should be installed between Pin 3 of the vehicle connector P7 and engine ground.