Lexus RX300 (MCU15). Service manual — part 239

DI–188

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

LEXUS RX300 (RM785E)

DTC

P1780

Park/Neutral Position Switch Malfunction
(Neutral Start Switch)

CIRCUIT DESCRIPTION

The neutral start switch detects the shift lever position and sends signals to the Engine & ECT ECU.
The Engine & ECT ECU receives signals (NSW, R, 2 and L) from the neutral start switch. When the signal
is not sent to the Engine & ECT ECU from the neutral start switch, the Engine & ECT ECU judges that the
shift lever is in D range.

DTC No.

DTC Detection Condition

Trouble Area

P1780

When driving under conditions (a) and (b) for 30 seconds or

more, the neutral start switch is ON (N range).

(2 trip detection logic)

(a) Vehicle speed: 70 km/h (44 mph) or more

(b) Engine speed: 1,500 – 2,500 rpm

S Short in neutral start switch circuit

S Neutral start switch

S Engine & ECT ECU

DI0CZ–18

D10062

P

Engine & ECT ECU

R

N

D

2

L

E6

9

8

7

16

14

13

E6

E6

E6

E6

E6

G–W

R–B

R–W

G–R

G–Y

G–W

R–W

1

2

5

7

4

8

Neutral Start Switch

3

R–L

IH1

10

B

D

B

B

C

C

D

J8 J/C

R–L

1G

1C

7

2

GAUGE

B–Y

W–L

6

1C

1

1A

AM1

Fusible Link Block

ALT

Battery

1

2

A

A

A

Instrument Panel J/B

Instrument Panel J/B

3

R–B

G–R

L–R

W

Ignition SW

2

4

Skid Control ECU

Skid Control ECU

6

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

DI–189

LEXUS RX300 (RM785E)

WIRING DIAGRAM

D10060

P

R

N

L

D

2

(+)

(–)

ON

DI–190

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

LEXUS RX300 (RM785E)

INSPECTION PROCEDURE

1

Read NSW, REVERSE, 2ND and LOW signals.

When using hand–held tester.
PREPARATION:
(a)

Remove the DLC3 cover.

(b)

Connect a hand–held tester to the DLC3.

(c)

Turn the ignition switch ON and hand–held tester main
switch ON.

CHECK:
Shift lever into the P, R, N, 2 and L ranges, and read the NSW,
REVERSE, 2ND and LOW signals on the hand–held tester.
OK:

Shift range

Signal

2

2ND OFF → ON

L

LOW OFF → ON

R

REVERSE OFF → ON

P, N

NSW OFF → ON

When not using hand–held tester.
PREPARATION:
Turn the ignition switch ON.
CHECK:
Measure voltage between terminals NSW, 2, L and R of Engine
& ECT ECU and body ground when the shift lever is shifted to
the following ranges.
OK:

Shift range

Tester connection

Specified value

P

P – Body ground

Battery voltage

R

R – Body ground

Battery voltage

N

N – Body ground

Battery voltage

D

D – Body ground

Battery voltage

2

2 – Body ground

Battery voltage

L

L– Body ground

Battery voltage

HINT:
*: The voltage will drop slightly due to lighting up of the back up
light.

OK

Proceed to next circuit inspection shown on
matrix chart (See page DI–160).

NG

F13412

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

DI–191

LEXUS RX300 (RM785E)

2

Check neutral start switch.

PREPARATION:
(a)

Jack up the vehicle.

(b)

Remove the neutral start switch.

CHECK:
Check continuity between each terminal shown below when the
shift lever is moved to each range.

Shift range

Terminal No. to continuity

P

1 – 3

6 – 9

R

2 – 3

–

N

3 – 5

6 – 9

D

3 – 7

–

2

3 – 4

–

L

3 – 8

–

OK:

There is continuity.

NG

Replace the neutral start switch.

OK

3

Check harness and connector between battery and neutral start switch, neutral
start switch and Engine & ECT ECU (See page IN–32).

NG

Repair or replace the harness and connector.

OK

Check and replace the Engine & ECT ECU
(See page IN–32).