1991 ACURA NSX Service Repair Manual

Idle Control System
Troubleshooting Flowchart

Alternator (ALT) FR Signal
This signals the ECM when the alternator is charging.
Inspection of ALT FR signal.
Connect the test harness be-
tween the ECM and connector.
Disconnect "D" connector from
the engine wire harness only, not
the ECM (see page 11-37).

Turn the ignition switch ON.

Measure voltage between D9 ( + ) terminal and A26 (-) ter-
minal.
Is there approx. 5 V?
Turn the ignition switch OFF.
Reconnect "D" connector to the
engine wire harness.
Warm up engine to normal oper-ating temperature (the cooling
fan comes on).
Measure voltage between D9( + ) terminal and A26 (-) ter-
minal.

Does the voltage decrease when

headlights and rear defogger are

turned on ?

Do the ECM Reset Procedure
(see page 11-35).
ALT FR signal is OK.(To page 11-93) Substitute a known-good ECM

and recheck. If prescribed

voltage is now available, replace
the original ECM.
Turn the ignition switch OFF.ProCarManuals.com

(From page 11-92)

Disconnect "D" connector from

ECM only, not the engine wire

harness.
Disconnect the negative battery
cable from the battery.

Check for continuity between D9

terminal and body ground.

Does continuity exist ?
Remove the harness covers.
Disconnect GRN connector from

the
ALT.
Connect WHT/RED wire to body

ground.
Check for continuity between D9

terminal and body ground.

Does continuity exist ?
Repair open in WHT/RED wire between ECM (D9) and ALT.

See ALT inspection
(see section 23). Repair shor in WHT/RED wire
between ECM (D9) and ALT.
Does continuity exist ?

Check for continuity between D9

terminal and body ground.
Disconnect GRN connector from

the
ALT. Remove the harness covers.
See ALT inspection(see section 23).
GRN CONNECTORProCarManuals.com

Idle Control System
Troubleshooting Flowchart Automatic Transaxle (A/T) Gear Position
Signal
This signals the ECM when the transmission is in Neutral or Park.
Inspection of A/T gear position

signal.

Turn the ignition switch ON.
Observe the A/T gear position in-
dicator and select each position
separately.

Does the indicator light properly?
Turn the ignition switch OFF.
Connect the test harness be-
tween the ECM and connector.
Disconnect "B" connector from

the engine wire harness only, not

the ECM (see page 11-37).

Turn the ignition switch ON.

Measure voltage between B7

( + ) terminal and A26 (-) ter-

minal.
Is there approx. 10V?
Turn the ignition switch OFF.
Reconnect "B" connector to the
engine wire harness.
Turn the ignition switch ON.
(To page 11-95) See A/T gear position switch in-
dicator inspection (see section
14).
Substitute a known-good ECM
and recheck. If prescribed voltage is now available, replace
the original ECM.ProCarManuals.com

(From page 11-94)
Measure voltage between B7 (+)

terminal and A26 (-) terminal
with the transmission in and

range individually.

Is there less than 1.0 V?

Measure voltage between B7 ( + ) terminal and A26 (-) ter-

minal with the transmission in

gear.

Is there approx. 10 V?
A/T gear position signal is OK. Repair short in LT GRN wire be-
tween ECM (B7) and gauge

assembly.

Repair open in LT GRN wire be-
tween ECM (B7) and gauge

assembly.ProCarManuals.com

Idle Control System

Troubleshooting Flowchart
Neutral Switch Signal (M/T)
This signals the ECM when the transmission is in neutral.
Inspection of neutral switch

signal.

Connect the test harness be-
tween the ECM and connectors
(see page 11-37).
Turn the ignition switch ON.
Measure voltage between B7 (+)
terminal and A26 (-) terminal in
neutral position.

Is there voltage?
Shift transmission in gear.
Is there approx. 10 V?
Neutral switch signal is OK.
Replace neutral switch (see sec-

tion
13). Is there approx. 10 V?
Reconnect "B" connector to
engine wire harness and discon-
nect 3P connector on the neutral

switch.
Is there approx. 10 V?
Disconnect "B" connector from
engine wire harness only, not the

ECM.

Repair open in LT GRN wire be-
tween ECM (B7) and neutral
switch or BLK wire between
neutral switch and G101 (located at right middle of

engine).
Is there voltage?
Connect LT GRN terminal to BLK

terminal.
Disconnect the 3P connector on
the neutral switch.
Replace neutral switch
(see section 13).
NEUTRAL SWITCH

LT GRN

BLK

Substitute a known-

good ECM and re-

check.
If prescribed voltage is
now available, replace
the original ECM.

Repair short in LT GRN
wire between ECM(B7) and the neutral

switch.ProCarManuals.com

Idle Control System

Troubleshooting Flowchart
Clutch Switch Signal (M/T)
This signals the ECM when the clutch is engaged. Inspection of clutch switch

signal.

Connect the test harness be-
tween the ECM and connectors
(see page 11-37).
Turn the ignition switch ON.
Measure voltage between C7 (+)
terminal and A26 (-) terminal.
Is voltage less than 1.0 V?
Depress the clutch pedal.
Measure voltage between C7 (+)
terminal and A26 (-) terminal.
(To page 11-99) Turn the ignition switch OFF.
Disconnect the 3P connector
from the clutch switch.
Check for continuity between

the A terminal and C terminal on

the clutch switch.

Does continuity exist?

Turn the ignition switch ON.
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 (located behind left kick
panel).
Replace the clutch

switch.

Repair open in PNK
wire between ECM
(C7) and the clutch
switch.ProCarManuals.com

(From page 11-98)
Is there approx. 10 V?
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. 10 V?

Turn the ignition switch OFF.

Disconnect "C" connector from

engine wire harness only, not the
ECM.

Turn the ignition switch ON.

Is there approx. 10 V?
Substitute a known-good ECM
and recheck. If prescribed voltage is now available, replace
the original ECM. Replace the clutch

switch.

Repair short in PNK
wire between ECM
(C7) and the clutch
switch.ProCarManuals.com

Idle Control System

Troubleshooting Flowchart

This signals the ECM when the engine is cranking.
Inspection of starter switch
signal.
Connect the test harness be-
tween the ECM and connectors
(see page 11-37).
Measure voltage between C11(+) terminal and A26 (-) terminal

with the ignition switch in the

start position.

Is there battery voltage ?
Starter switch signal is OK.
NOTE:

M/T: Clutch pedal must be depressed. A/T: in or range.
Inspect No. 7 (7.5 A) fuse in the
under-dash fuse box.
Is the fuse OK?
Repair open in BLK/WHT wire
between ECM (C11) and No. 7
fuse. Replace the fuse.

Starter Switch Signal

BATTERY

VOLTAGE?ProCarManuals.com