relay ACURA NSX 1991 Service Repair Manual

Engine Coolant Refilling and Bleeding

CAUTION: When pouring engine coolant, be sure to

shut the relay box lid and not let coolant spill on the

electrical parts or the paint. If any coolant spills, rinse it

off immediately.

NOTE:

• Perform this maintenance when the engine is cool.

• Before replacing the coolant, turn the ignition ON,

slowly turn the climate control temperature knob to

90° and turn off the ignition. This will allow the

coolant in the heater to drain out with the rest of the

system.
1. Open the hood, the rear window and the engine

cover.

2. Remove the cover protecting the water pipes and

shift cables on the underside of the car.

3. Before removing the expansion tank cap, first

loosen the cap to lower pressure.

CAUTION: Do not remove the expansion tank cap

when engine is hot. The coolant is under pressure

and may blow out and scald you. Open the cap

slowly when the engine is cool.

4. Loosen the drain plug in the bottom of the radiator,

and drain the coolant.

5. Remove the two drain bolts from the water pipes,

and drain the coolant.

WASHERS

Replace.

DRAIN BOLTS

15 N-m (1.5 kg-m, 11 Ib-ft)
DRAIN HOLE
DRAIN PLUGProCarManuals.com

Component Location s
Index
CLUTC H SWITC H (M/ T only )
Troubleshooting , pag e 11-12 4
ACCELERATOR POSITIO N (AP )
SENSO R
THROTTL E CABL EInspection/Adjustment , pag e 11-15 0
Installation , pag e 11-15 0
PGM-F I
MAI N RELA Y
Rela y Testing , pag e 11-14 3
Troubleshooting , pag e 11-14 4
THROTTLE VALVECONTROL MOTOR RELAY
Troubleshooting , pag e 11-11 2
ENGIN E CONTRO L MODUL E (ECM )
Self-diagnosti c Procedures , pag e 11-3 8
Troubleshooting , pag e 11-6 1, and 11-62 SERVIC
E CHEC K CONNECTO R (2P )
Self-diagnosti c Procedures , pag e 11-3 8
DAT A LIN K CONNECTO R (16P )
Self-diagnosti c Procedures , pag e 11-3 8
For Troubleshooting of DTC related components, see chart on page 11-52.
ProCarManuals.com

II. Engine Control Module (ECM) Reset Procedure

Either of the following actions, will reset the ECM.

• Using the OBD-II scan tool or Honda PGM Tester to clear the ECM's memory.

NOTE: See the OBD-II scan tool or Honda PGM Tester user's manuals for specific operating instructions.

• Turn the ignition switch OFF. Remove the CLOCK (7.5 A) fuse from the under-hood fuse/relay box for 10 seconds.

UNDER-HOOD

FUSE/RELAY BOX
CLOCK

(7.5 A) FUSE

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

1. Remove the SCS Service Connector if it is connected.

NOTE: If the SCS service connector is connected and there are no DTCs stored in the ECM, the MIL will stay on

when the ignition switch is turned on.

2. Do the ECM Reset Procedure.

3. Turn the ignition switch OFF.

4. Disconnect the OBD-II scan tool or Honda PGM Tester from the Data Link Connector,ProCarManuals.com

PGM-FI System

System Description

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.

Throttle Valve Control

The ECM controls the throttle valve control motor based on accelerator pedal position, TCS control unit and various sig-

nals. The ECM also controls the idle control function, cruise control function, and other functions with the throttle valve

control.

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 Electronic

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

Engine Control Module (ECM)

NOTE: If this symptom is intermittent, check for a loose No. 5 BACK-UP LIGHTS, ALTERNATOR,

TURN SIGNALS (15 A) fuse in the under-dash fuse/relay box, a poor connection at ECM terminal

A7, or an intermittent open in the BLU wire between the ECM (A7) and the gauge assembly.

Is the low oil pressure light on?

Try to start the engine.

Does the engine start?

Check for an open in the wire or

bulb:

1. Turn the ignition switch OFF.

2. Connect the ECM connector ter-

minal A7 to body ground with a

jumper wire.

3. Turn the ignition switch ON (II).

Is the MIL on?

Substitute a known-good ECM,

and recheck. If symptom/indica-

tion goes away, replace the origi-

nal
ECM.
— Repair short in the wire

between No. 5 BACK-UP

LIGHTS, ALTERNATOR, TURN

SIGNALS (15 A) fuse and

gauge assembly.

— Replace No. 5 BACK-UP

LIGHTS, ALTERNATOR, TURN

SIGNALS (15 A) fuse.

ECM CONNECTOR A (26P)

Check for an open in the wires

(PG line):

1. Turn the ignition switch ON (II).

2. Measure voltage between

body ground and ECM connec-

tor terminals A12 and A25 indi-

vidually.
WIRE SIDE OF FEMALE TERMINALS

Is there less than 1.0 V?
Repair open in the wire(s)

between ECM and G101 (located

at intake manifold) that had

more than 1.0V.

— Repair open in the wires

between ECM (A7) and gauge

assembly.

— Replace the MIL bulb.
WIRE SIDE OF FEMALE TERMINALS
ECM CONNECTOR A (26P)
Substitute a known-good ECM

and recheck. If symptom/indica-

tion goes away, replace the origi-

nal
ECM.
Turn the ignition switch ON (II).
The Malfunction Indicator Lamp

(MIL) never comes on (even for

two seconds) after ignition is

turned ON (II).ProCarManuals.com

(From pag e 11-62 )
Chec k fo r a shor t i n th e wire s
(MI L line) :
1. Tur n th e ignitio n switc h OFF .2. Disconnec t th e EC M connec -tor A (26P) .3. Tur n th e ignitio n switc h O N (II) .
Is th e MI L ON ?Repai r shor t t o bod y groun d i n
th e wir e betwee n th e EC M (A7 )
and MIL .
Substitut e a known-goo d EC M
an d recheck . I f symptom/indica -
tio n goe s away , replac e th e origi -
nal ECM .
(From pag e 11-62 )
Inspec t ACG(S ) (2 0 A ) fus e i n th e
engin e compartmen t fuse/rela y
box.
Is th e fus e OK ? Repai
r shor t i n th e wir e
betwee n ACG(S ) (2 0 A ) fus e
an d PGM-F I mai n relay .
Replac e ACG(S ) (2 0 A ) fuse .
Inspec t I G COI L (3 0 A ) fus e i n th e
engin e compartmen t fuse/rela y
box.
Is th e fus e OK ? Repai
r shor t i n th e wir e
betwee n I G COI L (3 0 A ) fus e
an d PGM-F I mai n relay .
Replac e IG COI L (3 0 A ) fuse .
Chec k fo r a shor t i n a sensor :
1. Tur n th e ignitio n switc h O N (II) .2. Disconnec t th e 3 P connecto r
o f eac h senso r on e a t time :
• MA P senso r
• T P senso r
• EG R valv e lif t senso r
Doe s th e MI L remai n ON ? Replac
e th e senso r tha t cause d
the ligh t t o g o out .
(To pag e 11-64 )
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PGM-FI Syste m
Engine Contro l Modul e (ECM )
(From pag e 11-63 )
Chec k fo r a shor t i n th e A P sen -
sor:1. Tur n th e ignitio n switc h OFF .2. Connec t th e SC S servic e con -
nector .
3 . Disconnec t th e A P senso r 3 P
connector .
4. Tur n th e ignitio n switc h O N (II) .
Is DT C P124 6 and/o r P124 7
indicated ?
Chec k fo r a shor t i n th e wire s
(VC C lines) :
1. Tur n th e ignitio n switc h OFF .2. Disconnec t th e EC M connec -tor D (22P ) an d F (26P) .3. Chec k fo r continuit y betwee nbody groun d an d EC M con -necto r terminal s D10 , F 1 an dF14 individually .
Is ther e continuity ?
I s ther e batter y voltage ?
Chec k fo r a n ope n i n th e wire s
(L G lines) :
1 . Reconnec t al l senso r connec -
tors.2. Reconnec t th e EC M connecto rD (22P ) F (26P) .3. Tur n th e ignitio n switc h O N (II) .4. Measur e voltag e betwee n
bod y groun d an d EC M connec -
tor terminal s A2 6 an d B 9 indi -vidually .
I s ther e les s tha n 1. 0 V ?
Substitut e a known-goo d EC M
an d recheck . I f symptom/indica -
tio n goe s away , replac e th e origi -
nal ECM .
Replac e th e A P sensor .
Repai r shor t t o bod y groun d
in th e wir e betwee n EC M(D10 ) an d throttl e angl e sen -
so r an d EG R valv e lif t sensor .
Repai r shor t t o bod y groun d in
th e wir e betwee n EC M (F1 )and MA P senso r o r Accelerato r
Positio n sensor .
Repai r shor t t o bod y groun d in
th e wir e betwee n EC M (F14 )
an d Accelerato r Positio n sen -
sor.
WIR E SID E O F FEMAL E TERMINAL S
Repai r ope n i n th e wire(s )
between EC M (A13 , C D an dPGM-F I mai n relay .
Chec k fo r poo r connection s
o r loos e wire s a t th e PGM-F I
mai n relay .
ECM CONNECTOR S
WIR E SID E O F FEMAL E TERMINAL S
Repai r ope n i n th e wire(s )
between EC M (A26 , B9 ) an dG10 1 tha t ha d mor e tha n 1. 0 V .
ProCarManuals.com

Drive By Wire System

System Description

The Drive By Wire System is an electronic throttle control system.

This system consists of the throttle valve control motor and Throttle Position (TP) sensor assembled in Throttle Body (TB),

the accelerator position sensor, and the Engine Control Module (ECM).

To THROTTLE

VALVE CONTROL

MOTOR RELAY

THROTTLE

VALVE

CONTROL

MOTOR

Drive By Wire System Functions:

Idle Control Function

When the engine is idling, the ECM controls the throttle valve control motor to maintain the proper idle speed according

to engine loads.

Acceleration Control Function

When the accelerator pedal is depressed, the ECM opens the throttle valve depending on the accelerator position sensor

signals.ProCarManuals.com

Idle Contro l Syste m
Air Conditionin g Signa l
(From pag e 11-117 )
I s ther e a clickin g nois e fro m th e
A/ C compresso r clutch ?
Chec k fo r th e operatio n o f th e
A/C :1. Star t th e engine .
2 . Tur n th e blowe r switc h ON .
3 . Tur n th e A/ C switc h ON .
Doe s th e A/ C operate ?
Ai r conditionin g signa l i s OK . A/
C CLUTC H RELA Y 4P CONNECTO R
Chec k fo r a n ope n in th e wire :
Momentaril y connec t th e No . 4 ter -
mina l o f th e 4 P connecto r o n th e
A/ C clutc h rela y t o bod y groun d
severa l times .
WIRE SID E O F
FEMAL E TERMINAL S
I s ther e a clickin g nois e fro m th e
A/ C compresso r clutch ? Se
e ai r conditione r inspectio n (se e
sectio n 22 ).
Repai r ope n in th e wir e betwee n
th e EC M (AS ) an d th e A/ C clutc h
relay.
ECM CONNECTOR S
Chec k fo r a n ope n in th e wire :
Measur e voltag e betwee n EC M
connecto r terminal s C 2 an d A26 . WIR
E SID E O F FEMAL E TERMINAL S
I s voltag e les s tha n 1. 0 V ? Repai
r ope n in th e wir e betwee n
th e EC M (C2 ) an d th e A/ C switch .
Substitut e a known-goo d EC M
an d recheck . I f symptom/indi -
catio n goe s away , replac e th e
origina l ECM .
Se e th e ai r conditione r inspec -
tio n (se e sectio n 22 ).
ProCarManuals.com

Starter Switch Signal

This signals the ECM when the engine is cranking.

Inspection of Starter Switch Sig-

nal.
NOTE:

• M/T: Clutch pedal must be depressed.

• A/T: Transmission in position.

ECM CONNECTORS

Measure voltage between ECM

connector terminals C6 and A26

with the ignition switch in the

start position.

WIRE SIDE OF FEMALE TERMINALS

Is there battery voltage?

Is the fuse OK?
Repair short in the wire

between the ECM (C6) and

the No. 7 STARTER SIGNAL

(7.5 A) fuse or the PGM-FI

main relay.

Replace the No. 7 STARTER

SIGNAL (7.5 A) fuse.
Starter switch signal is OK.

Repair open in the wire between

the ECM
(C6)
and the No. 7

STARTER SIGNAL (7.5 A) fuse.
Inspect the No. 7 STARTER SIG-

NAL (7.5 A) fuse in the under-

dash fuse box.ProCarManuals.com