Diagnostic Procedure

All engine control systems work together, if one system is not performing as it should then a driveability problem will occur. All systems that will cause a driveability problem will be included in the driveability tests.

Engine control systems must be evaluated for their effect on each other when one system is not operating properly. If one system is bad it may cause other systems to malfunction. Driveability tests will check all engine control systems in a sequence. Test conclusions will only apply to one system.

In some cases engine control systems will not be checked. If the SMEC monitors an engine control system, and no fault code is stored, then there is no need to check that particular system.

If an engine function is not monitored by the SMEC, then a trouble code will not be stored. This will require manual checking to determine operation of that non-monitored system. Some system failures will produce certain fault code combinations. The driveability tests will be very specific on what the problem is. The driveability tests are designed to diagnose problems as the vehicle owner experienced them.

During tests vehicle must have a fully charged battery. When performing a cold test, engine must not be started for at least 7 hours. When measuring for voltage or a continuity check at the SMEC 60-pin or 14-pin connectors, probe terminal side of connectors.

NOTE: DO NOT use test light in place of a voltmeter, damage to electronic components may result.

If the "CHECK ENGINE" light comes on, or if a driveability problem occurs, the probable cause can be determined by entering "On-Board Diagnostics" and recording trouble codes. A DRB-II Tester (C-4805 ) or the flashing "CHECK ENGINE" light may be used in displaying trouble codes. However, the "CHECK ENGINE" light is limited in its diagnostic capabilities.

Once trouble codes are known, refer to TROUBLE CODES in this article to determine the questionable circuit. Then use the wiring diagram and connector identification figures to locate testing points for each circuit. Test circuits and repair as necessary. To erase fault codes, refer to ERASING CODES FROM SMEC MEMORY in this article.