Lexus RX300 (MCU15). Service manual — part 237

DI–180

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

LEXUS RX300 (RM785E)

DTC

P1520

Stop Light Switch Signal Malfunction

CIRCUIT DESCRIPTION

The purpose of this circuit is to prevent the engine from stalling, while driving in lock–up condition, when
brakes are suddenly applied.
When the brake pedal is operated, this switch sends a signals to Engine & ECT ECU. Then the Engine &
ECT ECU cancels operation of the lock–up clutch while braking is in progress.

DTC No.

DTC Detecting Condition

Trouble Area

P1520

No stop light switch signal to Engine & ECT ECU during driv-

ing.

(2 trip detection logic)

S Open or short in stop light switch circuit

S Stop light switch

S Engine & ECT ECU

WIRING DIAGRAM

See page DI–111.

INSPECTION PROCEDURE

See page DI–111.

DI0CW–07

D03444

2

1

LG

L

5

E6

4

Engine & ECT ECU

NT+

NT–

E6

Input Turbine
Speed Sensor

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

DI–181

LEXUS RX300 (RM785E)

DTC

P1725

NT Revolution Sensor Circuit Malfunction
(Input Turbine Speed Sensor)

CIRCUIT DESCRIPTION

This sensor detects the rotation speed of the input turbine. By comparing the input turbine speed signal (NT)
and the counter gear speed sensor signal (NC), the Engine & ECT ECU detects the shift timing of the gears
and appropriately controls the engine torque and hydraulic pressure in response to various conditions, thus
performing smooth gear shifting.

DTC No.

DTC Detecting Condition

Trouble Area

P1725

The Engine & ECT ECU detects conditions (a), (b), (c) and (d)

continuity for 5 secs or more.

(1 trip detection logic)

(a) Vehicle speed: 50 km/h (20 mph) or more

(b) 2nd, 3rd or O/D gear

(c) Solenoid valves and neutral start switch are normal

(d) NT < 300 rpm

S Open or short in input turbine (NT) speed sensor circuit

S Input turbine (NT) speed sensor

S Engine & ECT ECU

WIRING DIAGRAM

DI3JP–05

D03337

NT

–

NT

+

Q08218

Magnet

DI–182

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

LEXUS RX300 (RM785E)

INSPECTION PROCEDURE

1

Check resistance between terminals NT

+

and NT

–

of Engine & ECT ECU.

PREPARATION:
Disconnect the connector from Engine & ECT ECU.
CHECK:
Check resistance between terminals NT

+

and NT

–

of Engine &

ECT ECU.
OK:

Resistance: 620 ± 60 Ω

OK

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

NG

2

Check input turbine speed sensor.

PREPARATION:
Remove the input turbine speed sensor from transaxle.
CHECK:
(a)

Measure resistance between terminals 1 and 2 of speed
sensor.

(b)

Check voltage between terminals 1 and 2 of the speed
sensor when a magnet is put close to the front end of the
speed sensor then taken away quickly.

OK:

(a) Resistance: 620 ± 60 Ω
(b) Voltage is generated intermittently.

HINT:
The voltage generated is extremely low.

NG

Replace the input turbine speed sensor.

OK

Check and repair the harness and connector
between Engine & ECT ECU and input turbine
speed sensor (See page IN–32).

D03444

2

1

G

R

24

E8

23

Engine & ECT ECU

NC

+

NC–

E8

Counter Gear
Speed Sensor

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

DI–183

LEXUS RX300 (RM785E)

DTC

P1730

NC Revolution Sensor Circuit Malfunction
(Counter Gear Speed Sensor)

CIRCUIT DESCRIPTION

This sensor detects the rotation speed of the counter gear. By comparing the counter gear speed signal (NC)
and the direct clutch speed sensor signal (NT), the Engine & ECT ECU detects the shift timing of the gears
and appropriately controls the engine torque and hydraulic pressure in response to various conditions, thus
performing smooth gear shifting.

DTC No.

DTC Detecting Condition

Trouble Area

P1730

The Engine & ECT ECU detects conditions (a), (b), (c) and (d)

continuity for 5 secs or more.

(1 trip detection logic)

(a) Vehicle speed: 50 km/h (20 mph) or more

(b) 2nd, 3rd or O/D gear

(c) Solenoid valves and neutral start switch are normal

(d) NC < 300 rpm

S Open or short in NC revolution sensor circuit

S Counter gear speed sensor

S Engine & ECT ECU

WIRING DIAGRAM

DI3JQ–06