Honda Prelude 1993 Service Manual page 297

4. A/C Compressor Clutch Relay
When the ECM receives a demand for cooling from the air conditioning system, it delays the compressor Jrom being
energized, and enriches the mixture to assure smooth transition to the A/C mode.
5. Evaporative Emission (EVAP) purge Control Solenoid Valve
when the engine coolant temperature is betow 1 67 o F (75 "Cl IH22A'| engine (USA: Si VTEC/Canada: SR-V): 1
bg oF
(70oC)1, the ECM supplies a ground to the EVAP purge control solenoid valve which
cuts vacuum to the EVAp purge
control diaphragm valve.
6.
Intake Air Bypass (lAB) Control Solenoid Valve
When the engine speed is below 4,8OO rpm IH22A1 engine (USA: Si VTEC/Canada: SR-V): 4,600 rpml, the IAB
control solenoid valve is activated by a signal from the ECM, intake air tlows through the long intake path, then high
torque is delivered At speeds higher than 4,8OO (or 4,600) rpm, the solenoid valve is deactivated by the ECM.
and
intake air flows through the short intake path in order to reduce the resistance in airflow.
7. Intake Control Solenoid Valve
When the engine speed is below 4,000 rpm, the ECM supplies a ground to the intake control solenoid valve. This
opens the solenoid valve sending intake manifold vacuum to the intake control diaphragm.
8. Exhaust Gas Recirculation {EGR) Control Solenoid Valve
when the EGR is required tor control of oxides of nitrogen (NOx) emission, the ECM supplies ground to the EGR
control solenoid valve which supplies fegulated vacuum to the EGR valve.
9. Alternator (ALT) Control
The system controls the voltage generated at the altemator in accordance with the electrical load and drive mode,
and reduces the engine load to improve the fuel economv.
ECM tail-safe/back-up Functions
1. Fsil-safe Function
When an abnormality occurs in a signal from a sensor, the ECM ignores that signal and assumes a pre-programmed
value fof that sensot that allows the engine to continue to run.
2. Back-uD Function
When an abnormality occurs in the ECM itself, the fuel injectors are controlled by a back-up circuit indeDendent ot
the system in order to permit minimal driving.
3. Self-diagnosis Function IMalfunction Indicator Lamp (MlL]1
When an abnotmality occurs in a signal from a sensor, the ECM lights the MIL and stores the code in erasable memory.
When the ignition is initially turned on, the ECM supplies ground tor the MIL for two seconds to check the MIL bulb
condition.
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