Data Link Connector: Description and Operation

Diagnosis And Test Switch Terminals:

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 self-diagnosis code and at the same time fixes the ON time of ISC solenoid valve constant.

TEST SWITCH TERMINAL
The test switch terminal is included in the monitor connector. When this terminal is grounded, ECM sets the ignition timing to the initial ignition timing.

When both test switch terminal and diagnosis switch terminal are grounded, ECM outputs A/F duty through the A/F duty check terminal. Also, "CHECK ENGINE" light stays ON at this time, but it is nothing abnormal.