Diagnostic Mode Switch/Connector: Description and Operation

Diagnosis Switch Terminal
The diagnosis switch terminal is included in the monitor coupler installed under the instrument panel at the passenger's seat side. When the diagnosis switch terminal is grounded, a diagnosis signal is fed to ECM (PCM) which then outputs idle air control duty (IAC 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 (PCM) fixes the ignition timing to initial one.

When both test switch terminal and diagnosis switch terminal are grounded, ECM (PCM) outputs A/F duty through the duty output terminal.