Serial Data

Terminal "E" of the underdash ALDL connector allows access to a variety of C-3 system sensor circuit information, using several types of aftermarket testers. While this information, known as "Serial Data," does not make use of diagnostic charts unnecessary, understanding what each position on the tester used measures and the function of the circuit involved can be useful in obtaining information that might otherwise prove time consuming or impossible to obtain using other test procedures.

Serial data access can be useful in obtaining information regarding intermittent malfunctions, as the tool can be installed and monitored while operating the vehicle under the conditions where the malfunction was reported to occur. If the malfunction seems to be related to specific functions that are monitored by the access tool, the system can be checked in the applicable positions, under actual operating conditions. If the malfunction is not related to any specific area, the system can be monitored in all tester positions for a period of time or under a group of operating conditions. This allows the technician to observe the system and monitor changes in tester readings that may indicate a system malfunction.

Serial data provided through the connector "E" terminal includes readings from the park/neutral switch, throttle position sensor, MAP, BARO and differential pressure sensors, coolant temperature sensor, vehicle speed sensor and oxygen sensor. When the access tool is installed, the "CHECK ENGINE" lamp will flash rapidly, indicating that serial data is being transmitted. In addition, the timer that holds the system in "OPEN LOOP" will be rendered inoperative and the system will operate in "CLOSED LOOP" as soon as the engine is started. Therefore, all related systems will be controlled as though the system was in CLOSED LOOP, and must be tested accordingly. For complete information regarding the operation of access tools and their affect on the C-3 system, refer to tester manufacturer's instructions.