sensor ACURA NSX 1991 Service Repair Manual

Speedometer/Trip Meter/Odometer
Troubleshooting (cont'd)
(From previous page)
Reconnect the 3-P connector at
the vehicle speed sensor (VSS).

Raise the rear of the car and sup-

port it with stands.

Back-probe the YEL/RED wire and

connect it to body ground through a voltmeter.

Put the car in neutral with key ON.

Slowly rotate one wheel with the
other wheel blocked. Does voltage pulse from 0 to about 12 V?
Disconnect the 30-P connector at
the speedometer.

Back-probe the YEL/RED wire and

connect it to body ground through a voltmeter.
Slowly rotate one wheel with the
other wheel blocked.
Does the volt meter indicate pulsing voltage?

Replace the speedometer.
Repair open in the YEL/RED wire,

between the VSS and the

speedometer.
Replace the VSS (see page

23-133).ProCarManuals.com

Blown No. 5 (10 A) fuse
(In the under-dash fuse box)
Blown No. 34 (15 A) fuse
(In the under-dash fuse box)
Safety indicator input
Safety indicator (Diodes)Brake light failure sensorDoor switch
Trunk latch switch
Retractable headlight control unit
(see page 23-174)
Poor ground
Open circuit, loose or disconnected
terminalsProCarManuals.com

ACTUATOR ASSEMBLY

Test, page 23-302

Cable Adjustment,

page 23-303

VEHICLE SPEED SENSOR (VSS)
Test, page 23-129ProCarManuals.com

Cruise Control

Description

The cruise control system uses mechanically and elec-

trically operated devices to maintain vehicle speed at a

setting selected by the driver.

The cruise control unit receives command signals from

the cruise control main switch and the cruise control

set/resume switch. It receives information about

operating conditions from the brake switch, ECM, vehi-

cle speed sensor (VSS), the clutch switch (with manual

transmission), or the A/T gear position switch (with

automatic transmission). The cruise control unit sends

operational signals to the devices that regulate the

throttle position. The throttle position maintains the

selected vehicle speed. Essentially, the control unit

compares the actual speed of the vehicle to the

selected speed. Then, the control unit uses the result of

that comparison to open or close the throttle.

The brake switch releases the system's control of the

throttle at the instant the driver depresses the brake

pedal. The switch sends an electronic signal to the con-

trol unit when the brake pedal is depressed; the control

unit responds by allowing the throttle to close. The

clutch switch (manual transmission) or the A/T gear

position switch (automatic transmission) sends a

disengage signal to the control unit that also allows the

throttle to close.
Operation:

The cruise control system will set and automatically

maintain any speed above 30 mph (45 kph). To set,

make sure that the main switch is in the "ON" position.

After reaching the desired speed, press the set switch.

The cruise control unit will receive a set signal and, in

turn, will actuate the cruise control actuator. When the

set switch is depressed and the cruise control system is

on, the "cruise control" ON indicator in the gauge

assembly will light up. You can cancel the cruise control

system by pushing the main switch to "OFF". This

removes power to the control unit and erases the set

speed from memory. If the system is disengaged tem-

porarily by the brake switch, clutch switch, or A/T gear

position switch and vehicle speed is still above 30 mph,

press the resume switch. With the resume switch

depressed and the set memory retained, the vehicle

automatically returns to the previous set speed.

For gradual acceleration without depressing the ac-

celerator pedal, push the resume switch down and hold

it there until the desired speed is reached. This will send

an acceleration signal to the control unit. When the

switch is released, the system will be reprogrammed for

the new speed. To slow down, depress the set switch.

This will send a deceleration signal to the control unit

causing the car to coast until the desired speed is reach-

ed. When the desired speed is reached, release the set

switch. This will reprogram the system for the new

speed.ProCarManuals.com

Component Locations

Index
FRONT KNOCK SENSOR
Troubleshooting, page 11-62
COOLANT TEMPERATURE (TW) SENSOR

Troubleshooting, page 11 - 48

EGR VALVE

Troubleshooting,
page 11-128
FUEL PUMP RESISTOR

Inspection, page 11-106

CRANK/CYL SENSOR

Troubleshooting, page 11-46

CONTROL BOX
page 11-6 THROTTLE

ANGLE

SENSOR

Troubleshooting,
page 11-50
FAST IDLE VALVE

Inspection, page 11-83

EACV

Troubleshooting,

page 11-70 INJECTOR
RESISTOR

Testing, page 11-94

FRONT HEATED
OXYGEN (O2) SENSOR

Troubleshooting, page 11-32

INTAKE AIR TEMPERATURE
(TA) SENSOR

Troubleshooting, page 11-52

REAR KNOCK SENSOR

Troubleshooting, page 11 -62

REAR HEATED
OXYGEN (O2) SENSOR

Troubleshooting, page 11 -32

MAIN RELAY
Relay Testing, page 11-104

Inspection, page 11-105

ELECTRONIC CONTROL UNIT (ECU)

Troubleshooting, page 11-26
FUEL PUMP RELAY

Inspection, page 11-99ProCarManuals.com

System Description
Vacuum Connections
CONTROL

BOX

page 11-6

PURGE CONTROL
DIAPHRAGM
CHARCOAL
CANISTER
TO TWO-WAY
VALVE
CHAMBER
VOLUME
CONTROL
DIAPHRAGM

DASHPOT

DIAPHRAGMEGR VALVE FRONT OF
VEHICLE
EGR VALVE LIFT SENSOR
FUEL PRESSURE
REGULATOR

(cont'd)ProCarManuals.com

System Description

Vacuum Connections (cont'd)
Control Box
PURGE CUT-OFF
SOLENOID VALVE
Troubleshooting, page 11-137 CONSTANT VACUUM CONTROL (CVC)

VALVE

Troubleshooting, page 11-128

EGR CONTROL

SOLENOID VALVE

Troubleshooting,

page 11-128 MANIFOLD ABSOLUTE
PRESSURE (MAP) SENSOR

Troubleshooting, page 11-40

CHAMBER
VOLUME
CONTROL
SOLENOID

VALVE

Troubleshooting,

page 11-120
AIR CHAMBERProCarManuals.com

CHECK VALVE

AIR CHAMBER

CHAMBER VOLUME CONTROL SOLENOID VALVE

CHAMBER VOLUME CONTROL DIAPHRAGM

PCV VALVE

EGR VALVE

CONSTANT VACUUM CONTROL (CVC) VALVE

EGR CONTROL SOLENOID VALVE

CHARCOAL CANISTER

PURGE CUT-OFF SOLENOID VALVE

PURGE CONTROL DIAPHRAGM VALVE

TWO-WAY VALVE
FRONT OXYGEN (O2) SENSOR

REAR OXYGEN (O2) SENSOR

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

ELECTRONIC AIR CONTROL VALVE (EACV)

FAST IDLE VALVE

AIR CLEANER

FUEL INJECTOR

PRESSURE REGULATOR

FUEL FILTER

FUEL PUMP

FUEL TANK

DASHPOT DIAPHRAGM

DASHPOT CHECK VALVEProCarManuals.com

PGM-FI Control System

System Description
INPUTS ELECTRONIC CONTROL UNIT OUTPUTSCRANK/CYL SensorsMAP Sensor
TW Sensor
TA Sensor
Throttle Angle Sensor Oxygen SensorsEGR Valve Lift Sensor
Vehicle Speed Sensor
Ignition Timing Adjuster
Knock Sensers
A/T Fl Signals
TCS Signals

Starter Signal

Alternator FR Signal
Air Conditioning Signal
A/T Shift Position Signal M/T Neutral Switch Signal
M/T Clutch Switch Signal
Battery Voltage (IGN. 1)
Fuel Pump Terminal Voltage
VTEC Oil Pressure Switch

Signals

Injector Timing and Duration
Electronic Idle Control
Other Control Functions Ignition Timing Control
ECU Back-up Functions Injectors
Main Relay (Fuel Pump)
Fuel Pump Relay
Check Engine Light
EACV
A/C Compressor Clutch Relay

Igniter Unit

Purge Cut-Off Solenoid Valve
EGR Control Solenoid Valve
Chamber Volume Control Solenoid Valve
Radiator Fan Relay

Engine Compartment Fan Relay
VTEC Spool Valves
TCS Control Signals
Injector Tinning and Duration

The ECU contains memories for the basic discharge durations at various engine speeds and manifold pressures. The

basic discharge duration, after being read out from the memory, is further modified by signals sent from various sensors

to obtain the final discharge duration.

Electronic Air Control

Electronic Air Control Valve (EACV)

When the engine is cold, the A/C compressor is on, the transmission is in gear (A/T only) or the alternator is charging, the ECU
controls current to the EACV to maintain correct idle speed.

Ignition Timing Control
The ECU contains memories for basic ignition timing at various engine speeds and manifold pressures. Ignition timing
is also adjusted for coolant temperature.
A Knock Control System is also used. When detonation is detected by the knock sensor, the ignition timing is

retarded.

Other Control Functions
1. Starting Control

When the engine is started, the ECU provides a rich mixture.
2. Fuel Pump Control
When the ignition switch is initially turned on, the ECU supplies ground to the main relay which supplies current to

the fuel pump for two seconds to pressurize the fuel system.

When the engine is running, the ECU supplies ground to the mam relay which supplies current to the fuel pump.

When the engine is not running and the ignition is on, the ECU cuts ground to the main relay which cuts current
to the fuel pump.
Excellent engine performance is achieved through the use of VTEC (Variable Valve Timing and Lift Electronic Con-
trol System), intake manifold chamber control and discharge volume control of the fuel pump.
3. Fuel Cut-off Control During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at
speeds over 1,500 rpm.
Fuel cut-off action also takes place
when
engine speed exceeds,
8,300
rpm, regardless
of the
position
of the

throttle valve, to protect the engine from over-revving.ProCarManuals.com

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 70 °C (158 °F), the ECU supplies a ground to the purge cut-off solenoid valve

which cuts vacuum to the purge control valve.

6. Chamber Volume Control Solenoid Valve (CVCSV)

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 (EGR CSV)

When the EGR is required for control of oxides of nitrogen (NOx) emissions, the ECU supplies ground to the EGR CSV

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.ProCarManuals.com