1991 ACURA NSX relay

System Description
Electrical Connections

FUSES
CLOCK (7.5 A)*

ACG
(120 A)**

ACG(S) (20 A)**

IG COIL (30 A)**

No. 2 (15 A)

No. 5 (10 A)
No.
4(15
A)

No. 7
(7.5
A)
In the under-hood
fuse/relay box In the engine
compartment
fuse/relay box

CKP/CYP

SENSOR

TO A/T
GEAR

POSITION
SWITCH

NEUTRAL

SWITCH
(M/T)

AUTO A/C

CONTROL

UNIT
CLUTCH
SWITCH
(M/T)
SERVICE

CHECK

CONNECTOR

A/C

PRESSURE

SWITCH A
A/C

PRESSURE

SWITCH B FUEL PUMP

RESISTORProCarManuals.com

System Description
System Connectors [Engine Compartment (Left Side)]
ENGINE WIREHARNESS C123
G103
C107
C106
ENGINE

COMPARTMENT
FUSE/RELAY

BOX

C108
C113
SIDE WIRE

HARNESS
C11
6
C532

C533
CONTROL
BOX

C534

C119
C121

C122
ProCarManuals.com

System Description
System Connectors [Front Compartment and Under-dash] (cont'd)

UNDER-HOOD
FUSE/RELAY

BOX
C464
C249

C446

C425

C439

C412

FLOOR

WIRE
HARNESS
SIDE

WIRE

HARNESS
UNDER-DASH
FUSE

BOX

C405

C406

C404

C318
C458
C228
FRONT

COMPARTMENT

WIRE
HARNESS
SUB RELAY

BOX AProCarManuals.com

System Description
System Connectors [Front Compartment and Under-dash] (cont'd)
C468
C244

C469
C245

FLOOR
WIRE

HARNESS

C523
C408
C524
C407

C521

C522

UNDER-DASH

FUSE

BOX

SIDE

WIRE

HARNESS

FRONT

COMPARTMENT

WIRE HARNESS

UNDER-HOOD

FUSE/RELAY

BOXProCarManuals.com

II. ENGINE CONTROL MODULE (ECM) Reset Procedure

1. Turn the ignition switch off.

2. Remove the CLOCK (7.5 A) fuse from the under-hood fuse/relay box for 10 seconds to reset ECM.

NOTE: Disconnecting the CLOCK fuse also cancels the radio preset stations and the clock setting. Make note of

the radio presets before removing the fuse so you can reset them.

III. Final Procedure (this procedure must be done after any troubleshooting)

1. Remove the Jumper Wire.

NOTE: If the Service Check Connector is jumped, the MIL will stay on.

2. Do the ECM Reset Procedure.

3. Set the radio preset stations and the clock setting.

(cont'd)
CLOCK

(7.5 A) FUSE

UNDER-HOOD

FUSE/RELAY BOXProCarManuals.com

PGM-FI System

System Description

INPUTS
ENGINE CONTROL MODULE (ECM)

OUTPUTS

FRONT HO2S

REAR HO2S

MAP Sensor

CKP/CYP Sensor

ECT Sensor

TP Sensor

IAT Sensor

VSS

FRONT KS

REAR KS

Ignition Timing Adjuster

EGR Valve Lift Sensor

A/T Fl Signals

TCS Signals

Starter Signal

ALT FR Signal

Air Conditioning Signal

A/T Gear Position Switch Signal

Neutral Switch Signal (M/T)

Clutch Switch Signal (M/T)

VTEC Pressure Switch

Battery Voltage (IGN.1)

Fuel Pump Terminal Voltage
Fuel Injectors

PGM-FI Main Relay (Fuel Pump)

Malfunction Indicator Lamp

IAC Valve

A/C Compressor Clutch Relay

ICM

EVAP Purge Control Solenoid Valve

Fuel Pump Relay

EGR Control Solenoid Valve

IAB Control Solenoid Valve

Engine Compartment Fan Relay

VTEC Solenoid Valve

TCS Control Signals

FRONT HO2S HEATER

REAR HO2S HEATER

PGM-FI System

The PGM-FI system on this model is a sequential multiport fuel injection system.

Fuel Injector Timing and Duration

The ECM 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.

Idle Air Control

Idle Air Control (IAC) Valve

When the engine is cold, the A/C compressor is on, the transmission is in gear (A/T only) or the alternator (ALT) is charg-

ing, the ECM controls current to the IAC valve to maintain correct idle speed.

Ignition Timing Control

The ECM contains memories for basic ignition timing at various engine speeds and manifold pressures. Ignition timing

is also adjusted for engine coolant temperature.

A knock control system is also used. When detonation is detected by the knock sensor (KS), the ignition timing is

retarded.

Other Control Functions

1. Starting Control

When the engine is started, the ECM provides a rich mixture by increasing fuel injector duration.

2. Fuel Pump Control

When the ignition switch is initially turned on, the ECM supplies ground to the PGM-FI main relay that supplies

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

When the engine is running, the ECM supplies ground to the PGM-FI main relay that supplies current to the fuel pump.

When the engine is not running and the ignition is on, the ECM cuts ground to the PGM-FI main relay which cuts

current to the fuel pump.

Excellent engine performance is achieved through the use of VTEC (Variable Valve Timing and Valve Lift Electron-

ic Control System), intake air bypass control and discharge volume control of the fuel pump.ProCarManuals.com

3. Fuel Cut-off Control

During deceleration with the throttle valve closed, current to the fuel 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.

4. A/C Compressor Clutch Relay

When the ECM receives a demand for cooling from the air conditioning system, it delays the compressor from being

energized, and enriches the mixture to assure smooth translation to the A/C mode.

5. Evaporative Emission (EVAP) Purge Control Solenoid Valve

When the engine coolant temperature is below 1 58 °F (70°C) 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 (IAB) Control Solenoid Valve

When the engine speed is below 4,800 rpm, the IAB control solenoid valve is activated by a signal from the ECM.

Intake air then flows through the smaller chamber, and hight torque is delivered. To increase air flow at engine speeds

higher than 4,800 rpm, the solenoid valve is deactivated by the ECM, and the intake air flows through the larger

chamber.

7. Exhaust Gas Recirculation (EGR) Control Solenoid Valve

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

control solenoid valve which supplies regulated vacuum to the EGR valve.

ECM fail-safe/back-up Functions

1. Fail-Safe Function

When an abnormality occurs in a signal from a sensor, the ECM ignores that signal and assumes a pre-programmed

valve for that sensor that allows the engine to continue to run.

2. Back-up Function

When an abnormality occurs in the ECM itself, the fuel injectors are controlled by a back-up circuit independent of

the system in order to permit minimal driving.

3. Self-diagnosis Function [Malfunction Indicator Lamp (MIL)]

When an abnormality occurs in a signal from a sensor, the ECM lights the MIL and stores the diagnostic trouble code

in erasable memory. When the ignition is initially turned in, the ECM supplies ground for the MIL for two seconds

to check the MIL bulb condition.ProCarManuals.com

PGM-FI System

Troubleshooting Flowchart
Engine Control Module (ECM) (cont'd)
Malfunction Indicator Lamp (MIL) stays on after two seconds.

Turn the ignition switch ON.

Connect the service check con-

nector terminals with a jumper

wire.
Does the MIL indicate
any Diagnostic Trouble

Code (DTC)?

Remove the jumper wire from the
service check connector.
Try to start the engine.Did the engine start?
Remove and inspect the ACG (S) (20 A) fuse in the engine compart-
ment fuse/relay box.
Is the fuse OK?
(To page 11-45) Go to self-diagnostic procedures
(see page 11-34).

Turn the ignition switch OFF.

Connect the test harness between

the ECM and connectors (see page 11-37).

Turn the ignition switch ON.
Measure voltage between C9 (+)

terminal and D22 (-) terminal.

Is there approx. 5V (A/T: 11 V)?
Repair short to body ground in
BLU wire between the ECM (C9),
TCM, EPS control unit, ABS con-
trol unit or TCS control unit and service check connector.
Repair open in BLU wire be-
tween ECM (C9) and service check connector.
Repair open in GRN/WHT wire
between service check con-
nector and ECM (D22).
Replace the fuse.
NOTE: After repair, disconnect the service check con-
nector jumper wire, test drive the car, and recheck the
MIL for a code. NOTE: When there is no code stored, the MIL will stay
on if the service check connector is jumped.
Connect the service
check connector termi-

nals with a jumper wire.

Measure voltage be-

tween C9 (+) terminal

and D22 (-) terminal.

Is there approx. 5 V(A/T:
11 V)?

Remove the jumper
wire from the service
check connector.
(To page 11-45)ProCarManuals.com