Computers and Control Systems: Testing and Inspection

Fig. 8 - Idle Speed Control System Diagram:

The CEC system should be considered as a possible source of trouble for engine performance, fuel economy and exhaust emission problems only after performing normal tests which would apply to a vehicle without the CEC system. An integral self-diagnostic system detects the problems which are most likely to occur.

When a fault occurs, the self-diagnostic system illuminates a "Check Engine" light on the instrument panel, and a trouble code will be flashed to identify the problem.

As a bulb and system check, the light will come on when the ignition switch is on with the engine stopped. It will also light and remain on for a few seconds when the engine is first started.

When the system detects a fault, the trouble code will be flashed five times. The code will not flash again unless the ignition is turned off and then the engine restarted.

A trouble code indicates a problem in a specific circuit. For example, Code 12 indicates a problem in the temperature sensing circuit. This includes the coolant temperature switch, wire harness, thermal electric switch (TES) and the MCU.

Because the self-diagnostic system cannot detect all possible faults, the absence of a flashed code does not necessarily mean that there is no fault in the system. To determine this, a system operational check is needed. This check is performed when the "Check Engine" display does not flash a code, but the system is suspected because no other reason can be found for the complaint. A test lamp, digital volt-ohmmeter, tachometer, vacuum gauge and jumper wires are needed to diagnose the system.


SERVICE NOTE: The idle speed control system, Fig. 8, and air injection system are interrelated with the CEC system. If a malfunction occurs in either of these systems, refer to Diagnostic Charts/Diagnostic tests 6, 7 and 8. The electronic ignition retard function of the ignition control module is also interrelated with the CEC system and should be diagnosed following Diagnostic Charts/Diagnostictest 4.