Honda Acura NSX 1991, Service Manual

Page: 201 / 1420

4. A/C Compressor Clutch Relay
When the ECU receives a demand for cooling from the air conditioning system (compressor control unit), it delays
the compressor from being energized, and enriches the mixture to assure smooth transition to the A/C mode.
5. Purge Cut-off Solenoid Valve
When the coolant temperature is below the ECU supplies a ground to the purge cut-off solenoid valve
which cuts vacuum to the purge control
6. Chamber Volume Control Solenoid Valve
When the engine rpm is below 4,800 rpm the CVCSV is activated by a signal from the ECU, intake air flows through
a smaller chamber, then high torque is delivered. At speeds higher than 4,800 rpm, both solenoid valves are deac-
tivated by the ECU, and intake air flows through the a larger chamber in order to increase airflow.
7. EGR Control Solenoid Valve
When the EGR is required for control of oxides of nitrogen emissions, the ECU supplies ground to the EGRCSV
which supplies regulated vacuum to the EGR valve.
ECU Back-up Functions
1. Fail-Safe Function
When an abnormality occurs in a signal from a sensor, the ECU ignores that signal and assumes a pre-programmed
value that allows the engine to continue to run.
2. Back-up Function
When an abnormality occurs in the ECU itself, the injectors are controlled by a back-up circuit independent of the
system in order to permit minimal diving.
3. Self-diagnosis Function (Check Engine light)
When an abnormality occurs in a signal from a sensor, the ECU lights the Check Engine light and stores the failure
code in erasable memory. When the ignition is initially turned on, the ECU supplies ground for the Check Engine light
for two seconds.
II-25