Data Link Connector: Description and Operation

DIAGNOSIS SWITCH TERMINAL
There are two diagnosis switch terminals; one included in the junction/fuse block and the other in the monitor coupler in the engine room. When either diagnosis switch terminal is grounded, a diagnosis signal is fed to ECM which then outputs diagnostic trouble code and at the same time outputs ISC duty (throttle valve opening) through duty output terminal.

TEST SWITCH TERMINAL
The test switch terminal is included in the monitor coupler. When this terminal is grounded, ECM fix the ignition timing to initial one. When both test switch terminal and diagnosis switch terminal are grounded, ECM outputs A/F duty through the duty output terminal.