Ignition Systems With C-4 Emissions: Operation

The electronic control module monitors the voltage output of oxygen sensor and other sensors to generate a control signal to the carburetor solenoid. The signal continually cycles the solenoid on and off.

On 3.8 liter V-6 engines, the ECM controls electronic spark timing. On 5.7 liter V-8 engines (VIN R), the ECM also controls the electronic module retard system. On Cadillac vehicles, the system works with the electronic spark selection system. If a problem exists, the built-in self-diagnosis system can detect and record failures in the electrical input circuits and within the micro-computer itself. This helps to pinpoint a particular circuit for further testing.

Should a problem exist, a "CHECK ENGINE" light on the instrument panel lights and a numerical code is stored in the computer memory to indicate why the light came on. The computer will temporarily adjust the system to continue vehicle operation. If the problem corrects itself, the light will go out, but the trouble code will be preserved in the computer's memory until the battery is disconnected or until the 20 amp. fuse has been removed momentarily.

The stored memory is programmed to erase itself after a preset number of trouble codes are accumulated. When "CHECK ENGINE" light appears, an under-dash black/white "test lead" with a green plastic connector and integral clip, should be grounded with the ignition "ON". This will cause the system to display any stored trouble codes by flashing the "CHECK ENGINE" light repeatedly to "spell out" each 2-digit trouble code.

For example, "Trouble Code 12" would be displayed by flashing the light one time, pausing, and then flashing two more times. After a longer pause, the code would repeat itself 2 more times. The code number flashed, identifies location of the problem.