check engine light ACURA NSX 1991 Service Owner's Guide

Idle Control System
Troubleshooting Flowchart Alternator FR Signal

This signals the PGM-FI ECU when the alternator is charging.

Inspection of Alternator FR

signal.

Connect the ECU test harness
between the ECU and connector.
Disconnect "D" connector from
the engine wire harness only, not

the ECU (page 11-21).

Turn the ignition switch ON.
Measure voltage between D9 ( + ) terminal and A26 (-) ter-

minal.

Is there approx. 5 V?
5V

D9

A26

Substitute a known-good ECU and recheck. If pre-
scribed voltage is now avail-
able, replace the original ECU.
Turn the ignition switch OFF.
Reconnect "D" connector to the
engine wire harness.
Warm up engine to normal oper-
ating temperature (cooling fan

comes on).
Voltage

D9

A26

Measure voltage between D9
( + ) terminal and A26 (-) ter-
minal.
Stop the engine.

Does the voltage decrease when

headlights and rear defogger are

turned on ?

Alternator FR signal is OK.

(To page 11-75)ProCarManuals.com

Idle Control System

Troubleshooting Flowchart
A/T Shift Position Signal

This signals the PGM-FI ECU when the transmission is in Neutral or Park.
Inspection of A/T Shift Position
Signal.

Turn the ignition switch ON.

Observe the A/T shift indicator and
select each position separately. See A/T Shift Position Indicator
Inspection.

Does the indicator light properly?

Turn the ignition switch OFF.
Connect the ECU test harness
between the ECU and connector. Disconnect "B" connector from
the engine wire harness only, not
the ECU (page 11-21).
10V

B7

A26

Turn the ignition switch ON.
Measure voltage between B7 ( + ) terminal and A26 (-) ter-

minal.

Is there approx. 10 V?
Substitute a known-good ECU

and recheck. If prescribed voltage

is now available, replace the

original ECU.

Turn the ignition switch OFF.

Reconnect "B" connector to the
engine wire harness.
Turn the ignition switch ON.
(To page 11-77)ProCarManuals.com

Idle Control System

Idle Speed Setting

Inspection/Adjustment
1. Start the engine and warm it up to normal operating temperature (the cooling fan comes on).
2. Connect a tachometer. Connect a tachometer to loop of igniter unit
secondary, or... 3. Disconnect the 2P connector from the EACV.

EACV

TACHOMETER
IGNITER
UNIT

4. Start the engine with the accelerator pedal slightlydepressed, then turn the headlights and rear defog-
ger ON. After the Check Engine light comes on,stabilize the rpm at 1000, then slowly release the
pedal until the engine idles. If the engine stalls, turn the idle adjusting screw
one turn counterclockwise and recheck.
5. Check idling with the headlights and rear defogger
on.

Idle speed should be:
Remove the rubber cap from the tachometer
connector and connect a tachometer.

TACHOMETER

RUBBER

CAP
Adjust the idle speed, if necessary, by turning
the idle adjusting screw. If the proper idle speed cannot be achieved,
clean the throttle body port with carburetor

cleaner.

IDLE ADJUSTING

SCREW

TACHOMETER CONNECTORProCarManuals.com

6. Turn the ignition switch OFF.

7. Reconnect the 2P connector on the EACV, then

remove CLOCK fuse in the under-hood fuse/relay

box for 10 seconds to reset ECU.

8. Restart and idle the engine with no-load conditions

in which the headlights, blower fan, rear defogger,

cooling fan, and air conditioner are not operating

for one minute, then check the idle speed.

Idle speed should be:ProCarManuals.com

Fuel Supply System

Pressure Regulator (cont'd)

3. Check that the fuel pressure rises when the vacuum hose from the regulator is disconnected again.
If the fuel pressure did not rise, check to see if it

rises with the fuel return hose lightly pinched.
If the fuel pressure still does not rise, replace the
pressure regulator.
Replacement
Do not smoke while working on fuel sys-

tem . Keep open flame away from work area.
1. Place a shop towel under pressure regulator, then
relieve fuel pressure (page
11-87).
2. Disconnect the vacuum hose and fuel return hose.
3. Remove the two 6 mm retainer bolts.
O-RING
Replace.

PRESSURE REGULATOR

RETURN HOSE
SHOP TOWEL

NOTE:
Replace the O-ring. When assembling the regulator, apply clean engine
oil to the O-ring and assemble it into its proper
position, taking care not to damage the O-ring.ProCarManuals.com

Air Intake System
Throttle Body

Description

The throttle body is of the single-barrel side-draft type.

The lower portion of the throttle valve is heated by
engine coolant which is fed from the cylinder head. Theidle adjusting screw which increases/decreases bypass
air and the canister/purge port are located on the top of
the throttle body. A dashpot is used to slow the throttle as it approaches the closed position.
Inspection

CAUTION: Do not adjust the throttle stop screw since

it preset at the factory.
1. Start the engine and allow it to reach normal operating temperature (cooling fan comes on).
2. Disconnect the vacuum hose (to the canister) from the top of the throttle body; connect a vacuum
gauge to the throttle body.

DASHPOT

DIAPHRAGM
THROTTLE

STOP SCREW

IDLE ADJUSTING

SCREW

THROTTLE
ANGLE SENSOR

VACUUM PUMP/GAUGE

A973X-041 -XXXXX
THROTTLE

VALVE

THROTTLE

ACTUATOR
3. Allow the engine to idle and check that the gauge
indicates no vacuum. If there is vacuum, check the throttle cable
(page 11-113).
4. Check that vacuum is indicated on the gauge when
the throttle is opened slightly from idle.
If the gauge indicates no vacuum, check the
throttle body port. If the throttle body port is clogged, clean it with carburetor cleaner.
5. Stop the engine and check that the throttle cable operates smoothly without binding or sticking. If there are any abnormalities in the above steps,
check for:
Excessive wear or play in the throttle valve
shaft.
Sticky or binding throttle lever at full close

position.
Clearance between throttle stop screw and
throttle lever at full close position.ProCarManuals.com

System Description
Tailpipe Emission
The emission control system includes a three-way catalytic converter, exhaust gas recirculation (EGR) system,
crankcase ventilation system and evaporative control

system.

The emission control system is designed to meet federal and
state emission standards.
Inspection

Do not smoke during this procedure. Keep
any open flame away from your work area.
1. Starting the engine and warm it up to normal operating temperature by driving the car on theroad.
2. Connect a tachometer.
3. Check idle speed and adjust the idle speed, if necessary (page 11-84).
4. Warm up and calibrate the CO meter according to the meter manufacturer's instructions.
5. Check idle CO with the headlights, heater blower, rear window defogger, cooling fan, and air conditioner off.
CO meter should indicate 0.1 % maximum.ProCarManuals.com

Emission Control System
Positive Crankcase Ventilation System
Description The Positive Crankcase Ventilation (PCV) system is
designed to prevent blow-by gas from escaping to theatmosphere. The PCV valve contains a spring-loaded

plunger. When the engine starts, the plunger in the PCV
valve is lifted in proportion to intake manifold vacuum and
the blow-by gas is drawn directly into the intake manifold.

PCV HOSE
BLOW-BY VAPOR
FRESH AIR
PCV VALVE
Inspection
1 Check the crankcase ventilation hoses and connec- tions for leaks and clogging.

BREATHER

PIPE

2. At idle, make sure there is a clicking sound from the PCV valve when the hose between PCV valve and

intake manifold in lightly pinched with your fingers or

pliers.
If there is no clicking sound, check the PCV valve
grommet for cracks or damage. If the grommet is
OK, replace the PCV valve and recheck.

PCV VALVE
PCV HOSE
Gently pinch here
BREATHER HOSE
FRONT OF
VEHICLEProCarManuals.com

Troubleshooting

Anti-lock Brake System Indicator Light

Temporary Driving Conditions:
1. The anti-lock brake system indicator light will come
on and the control unit memorizes the problem
under certain conditions.
NOTE: Problem codes are explained on pages
19 - 46.
The tire(s) adhesion is lost due to excessive cor-
nering speed.
Problem codes: 5, 5-4, 5-8. The vehicle loses traction when starting from a
stuck condition on a muddy, snowy, or sandy

road.
Problem code: 4-1, 4-2, 4-4, 4-8. When the parking brake is applied for more than
30 seconds while the vehicle is being driven.
Problem code: 2. The vehicle is driven on extremely rough road.
The anti-lock brake system is OK, if the anti-lock brake system indicator light goes off after the
engine is restarted.
ANTI-LOCK BRAKE SYSTEM INDICATOR LIGHT
2. If you receive a customer's report that the anti-lock brake system indicator light sometimes comes on,
check the system using the ALB checker to confirm
whether there is any trouble in the system.

See page 19 - 41.

3. The anti-lock brake system indicator light will come on and the control unit will store a problem codewhen there is insufficient battery voltage to the
control unit. An example would be when the bat-
tery is so weak that the car must be jump-started. After the battery is sufficiently recharged, the anti-lock brake system indicator light will work normally
after the engine is stopped and restarted.
However, after recharging the battery, the problem
code must be cleared from the control unit's
memory by disconnecting the ALB 2,3 (No. 32)
fuse for at least 3 seconds. Anti-lock Brake System Indicator Light Circuit:
CAUTION: Use only the digital multimeter to

check the system.

1. The indicator light does not go on when the ignition switch is turned on.
Check the following items. If they are OK, check
the control unit connectors. If not loose or disconnected, install a new control
unit and recheck:
Blown anti-lock brake system indicator light
bulb.
Open circuit in YEL wire between No. 5 (10 A)
fuse and gauge assembly. Open circuit in BLU/WHT wire between gauge
assembly and control unit. Loose component grounding of the control unit
to the body.
2. The anti-lock brake system indicator light remains ON after the engine is started, however the anti-lock brake system indicator light does not blink any
code or sub-code. Check the following items:
Loose or poor connection of the wire harness at

the control unit.

Faulty ALB 2,3 (No. 32) fuse.
Open circuit in WHT/BLK wire between ALB 2,3(No. 32) fuse and control unit.
Open circuit in YEL/BLK wire between fuse No.

4 (1 5 A) and control unit.

Short circuit in BLU/WHT wire between gauge
assembly and control unit. Open circuit in WHT/BLU wire between alter-

nator and control unit.

If the problem is not found substitute a known-good
control unit and recheck whether the warning light re-
mains ON.ProCarManuals.com

Comes on and remains on while running:
1. Stop the engine.
2. Turn the ignition switch on and make sure that the anti-lock brake system indicator light comes on.
3. Restart the engine and check the anti-lock brake system indicator light.
There is no problem in the anti-lock brake system, if the anti-lock brake system indicator light goes off. Go to step 4, if the anti-lock brake system indicator light remains on.

4. Stop the engine.
5. Disconnect the service check connector from the connector cover located under the glove box.
Connect the two terminals of the service check connector with a jumper wire.
6. Turn the ignition switch on, but do not start the engine. 7. Record the blinking frequency of the anti-lock brake system indicator light.
The blinking frequency indicates the problem code.
CAUTION: Before starting the engine, disconnect the jumper wire from the service check connector, or else the
Check Engine light will stay on with the engine running.

Turn the ignition

switch on
PROBLEM CODE:

4– 2

Main Code: 4

Sub-Code: 2
PROBLEM

CODE: 1

Main Code: 1

Sub-Code: none
PROBLEM CODE

7–2

Main Code: 7

Sub-Code: 2

Indicator

light on

Indicator

light off
Connect the

jumper wire
2

Second

pause
1

Second

pause
5 second

pause

5 second

pause

1

Second

pause

1 Second

NOTE:
The control unit can indicate three problem codes (one, two or three problems). If the anti-lock brake system indicator light does not light, see Troubleshooting of Anti-lock Brake System
Indicator Light Circuit page 19-44.
If you miscount the blinking frequency, turn the ignition switch off, then turn on to blink the anti-lock brake
system indicator light again. After the repair is completed, disconnect the ALB 2,3 (No. 32) fuse for at least 3 seconds to erase the control

unit's memory. Then turn the ignition key on again and recheck.
The memory is erased if the connector is disconnected from the control unit or the control unit is removed from
the body. After recording the main and sub-code (if applicable), refer to the Symptom-to-System Chart.

ANTI-LOCK BRAKE SYSTEM INDICATOR LIGHT
SERVICE CHECK CONNECTOR

JUMPER WIREProCarManuals.com