1991 ACURA NSX Service Repair Manual

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

(From page 11-74)
Disconnect "D" connector from
ECU only, not the engine wire
harness.
Disconnect the negative battery
cable from the battery.

Check for continuity between D9

terminal and body ground.
Continuity ?

Disconnect GRN connector from
the alternator.
Disconnect GRN connector from
the alternator. GRN CONNECTOR
Connect WHT/RED wire to body
ground.
Check for continuity between D9

terminal and body ground.

Check for continuity between D9

terminal and body ground.
Does continuity exist ?
Does continuity exist ? See Alternator Inspec-
tion.
See Alternator Inspec-

tion.

Repair open in WHT/RED wire
between ECU (D9) and alter-
nator. Does continuity exist ?
Repair short in WHT/RED wire
between ECU (D9) and alter-
nator.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

(From page 11-76)
Less than 1 V
B7

A26

Measure voltage between B7

( + ) terminal and A26 (-) ter-

minal with the transmission in
Is there less than 1 V?
Repair open in LT GRN wire
between ECU (B7) and gauge

assembly.

Repair open in GRN wire be-
tween the gauge assembly
and shift position console
switch.
Measure voltage between B7
( + ) terminal and A26 (-) ter-

minal with the transmission in
Less than 1 V

B7

A26

Is there less than 1 V?
Repair open in GRN/WHT wire
between gauge assembly and
shift position console switch.
Measure voltage between B7
(+) terminal and A26 (-) ter-
minal with the transmission in

gear.
Repair short in LT GRN wire bet-ween ECU (B7) and gauge
assembly.
Is there approx. 10V?
A/T shift position signal is OK.ProCarManuals.com

Idle Control System

Troubleshooting Flowchart

M/T Neutral Switch Signal
This signals the PGM-FI ECU when the transmission is in Neutral.
Inspection of M/T neutral Switch

Signal

Connect the ECU test harness
between the ECU and connector
(page 11-21).
0V
10V

B7

A26

Turn the ignition switch ON.
Measure voltage between B7 (+)
terminal and A26 (-) terminal in Neutral position.
Is there voltage? Disconnect the 3P connector on
the M/T neutral switch.

LT GRN
BLK

Connect LT GRN terminal to BLK
terminal.
Is there voltage?
Shift transmission in gear. Replace M/T neutral

switch.

Repair open in LT GRIM wire be-

tween ECU (B7) and M/T neutral
pressure switch or BLK wire be-
tween M/T neutral switch and G101.
Is there approx. 10 V? Disconnect "B" connector from
engine wire harness only, not the

ECU.

Is there approx. 10 V?
M/T neutral switch signal is OK. Substitute a known-
good ECU and re-

check.

If prescribed voltage is
now available, replace
the original ECU.
Reconnect "B" connector to
main wire harness and discon-
nect 3P connector on the M/T

neutral switch.

Is there approx. 10 V?
Repair short in LT GRN

wire between ECU
(B7)
and the M/T

neutral switch.
Replace M/T neutral switch.ProCarManuals.com

Idle Control System

Troubleshooting Flowchart
Clutch Switch Signal
This signals the PGM-FI ECU when the clutch is engaged.
Inspection of clutch switch

signal.

Connect the ECU test harnessbetween the ECU and connector
(page 11-21).
Less than 1 V?
10V

A26
C7

Turn the ignition switch ON.
Measure voltage between C7 (+)

terminal and A26 (-) terminal.

Is voltage less than 1 V?
Turn the ignition switch OFF.

Disconnect the 3P connector
from the clutch switch.
BLK

PNK

Check for continuity between
the A terminal and B terminal on

the clutch switch.

Does continuity exist? Replace the clutch

switch.

Turn the ignition switch ON.

Depress the clutch pedal.
Measure voltage between C7 (+)

terminal and A26 (-) terminal.

(To page 11-81) Measure voltage between PNK
(+) terminal and body ground.
Is there approx. 10 V?
Repair open in BLK wire be-
tween the clutch switch and G401.
Repair open in PNK

wire between ECU
(C7) and the clutch

switch.ProCarManuals.com

(From page 11-80)
Is there approx. 10V?

Clutch switch signal is OK.
Turn the ignition switch OFF.
Disconnect the 3P connector
from the clutch switch.

Turn the ignition switch ON.

Measure voltage between C7 (+)
terminal and A26 (-) terminal with the clutch pedal depressed.
Is there approx. 10V? Replace the clutch

switch.

Turn the ignition switch OFF.

Disconnect "C" connector from
engine wire harness only, not the

ECU.

Turn the ignition switch ON.

Is there approx. 10V? Repair short in PNK
wire between ECU
(C7) and the clutch

switch.

Substitute a known-good ECU
and recheck. If prescribed

voltage is now available, replace

the original ECU.ProCarManuals.com

Idle Control System
Troubleshooting Flowchart

Starter Switch Signal

This signals the PGM-FI ECU when the engine is cranking.

Inspection of Starter Switch

Signal.

BATTERY

VOLTAGE?
C 11

A26

NOTE: Clutch pedal must be depress-
ed on M/T models.
Connect the ECU test harness
between the ECU and connector

(page 11-21).

Measure voltage between C11
(+) terminal and A26 (-) terminal
with the ignition switch in the
start position.

Is there battery voltage ?

Inspect No. 7 fuse.
Is No. 7 fuse OK ?

Replace fuse.

Repair open in BLK/WHT wire

between ECU (C11) and No. 7

fuse.

Starter switch signal is OK.ProCarManuals.com