Lexus RX300 (MCU15). Service manual — part 234

DI–168

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

LEXUS RX300 (RM785E)

DTC

P0750

Shift Solenoid A Malfunction
(SL1 Solenoid Valve )

DTC

P0755

Shift Solenoid B Malfunction
(SL2 Solenoid Valve)

DTC

P0765

Shift Solenoid D Malfunction
(S4 Solenoid Valve)

SYSTEM DESCRIPTION

The Engine & ECT ECU uses signals from the vehicle speed sensor to detect the actual gear position (1st,
2nd, 3rd or O/D gear).
Then the Engine & ECT ECU compares the actual gear with the shift schedule in the Engine & ECT ECU
memory to detect mechanical trouble of the shift solenoid valves and valve body.

DTC No.

DTC Detecting Condition

Trouble Area

P0750

P0755

P0765

During normal driving, the gear required by the Engine & ECT

ECU does not match the actual gear

(2 trip detection logic)

S SL1/SL2/S4 solenoid valve is stuck open or closed

S Valve body is blocked up or stuck

HINT:
Check the SL1 solenoid valve when DTC P0750 is output, check the SL2 solenoid valve when DTC P0755
is output and check S4 solenoid valve when DTC P0765 is output.

DI0CS–11

D03424 D03423

D03445
D03446

D03724

SL1 and SL2 Solenoid Valve

S4 Solenoid Valve

1

2

(+)

(–)

1

2

(–)

(+)

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

DI–169

LEXUS RX300 (RM785E)

INSPECTION PROCEDURE

1

Check SL1, SL2 or S4 solenoid valve.

PREPARATION:
(a)

Jack up the vehicle.

(b)

Remove the oil pan.

(c)

Remove the SL1, SL2 or S4 solenoid valve.

CHECK:
(a)

Check the solenoid resistance.
(1)

SL1 or SL2 solenoid valve:
Measure resistance between terminals 1 and 2 of
solenoid connector.

(2)

S4 solenoid valve:
Measure resistance between terminal 1 of solenoid
connector and solenoid body.

OK:

Resistance: 5.1 – 5.5 Ω

(b)

Check the solenoid operation.
(1)

SL1 or SL2 solenoid valve:
Connect the positive (+) lead with an 23 W bulb to
terminal 1 and the negative (–) lead to terminal 2 of
solenoid connector, then check the movement of
the valve.

(2)

S4 solenoid valve:
Connect the positive (+) lead with an 23 W bulb to
terminal 1 of solenoid connector and the negative
(–) lead to the solenoid valve body, then check the
movement of the valve.

OK:

The shift solenoid valve makes operation noise.

NG

Replace the solenoid valve.

OK

Check the valve body (See page DI–160).

DI–170

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

LEXUS RX300 (RM785E)

DTC

P0753

Shift Solenoid A Electrical Malfunction
(SL1 Solenoid Valve)

DTC

P0758

Shift Solenoid B Electrical Malfunction
(SL2 Solenoid Valve )

DTC

P0768

Shift Solenoid D Electrical Malfunction
(S4 Solenoid Valve)

CIRCUIT DESCRIPTION

Shifting from 1st to O/D is performed in combination with ON and OFF of the SL1 and SL2 solenoid valves
controlled by Engine & ECT ECU. If an open or short circuit occurs in either of the solenoid valves, the Engine
& ECT ECU controls the remaining normal solenoid valve to allow the vehicle to be operated smoothly (Fail
safe function).

DTC No.

DTC Detecting Condition

Trouble Area

P0753

P0758

The Engine & ECT ECU checks for an open or short circuit in

the SL1 and SL2 solenoid valves.

(a) When the solenoid is energized, the duty ratio exceed 75 %

(b) When the solenoid is not energized, the duty ratio is less

than 3 %.

P0768

The Engine & ECT ECU checks for an open or short circuit in

the S4 solenoid valve circuit when it changes.

The Engine & ECT ECU records DTC P0768 if condition (a) or

(b) is detected.

(a) When the solenoid is energized, the solenoid resistance is

8 Ω or less and is counted.

(b) When the solenoid is not energized, the solenoid resistance

is 100 kΩ or more and is counted.

S Open or short in SL1/SL2/S4 solenoid valve circuit

S SL1/SL2 S4 solenoid valve

S Engine & ECT ECU

HINT:
Check the SL1 solenoid valve when DTC P0753 is output, check the SL2 solenoid valve when DTC P0758
is output and check the S4 solenoid valve when DTC P0768 is output.

DI3JN–07

NORMAL

S4

SL1

SL2

Solenoid Valve

Gear

ON

OFF

ON

OFF

ON

OFF

OFF

OFF

OFF

ON

1st

2nd

3rd

O/D

SL1 SOLENOID MALFUNCTIONING

Driving at 3rd or O/D

Driving at 1st or 2nd

Solenoid Valve

Gear

X

X

X

X

ON

OFF

OFF

OFF

OFF

OFF

OFF

ON

3rd

3rd

3rd

O/D

Solenoid Valve

Gear

X

X

X

X

ON

ON

OFF

ON

OFF

ON

OFF

OFF

OFF

ON

ON

2nd

2nd

3rd

3rd

Solenoid Valve

Gear

SL2 SOLENOID
MALFUNCTIONING

ON

X

X

X

X

ON

OFF

OFF

OFF

OFF

OFF

3rd

3rd

3rd

O/D

Solenoid Valve

Gear

S4 SOLENOID
MALFUNCTIONING

X

X

X

X

ON

ON

OFF

ON

OFF

OFF

1st

2nd

3rd

3rd

Solenoid Valve

Gear

SL1 AND SL2 SOLENOID
MALFUNCTIONING

X

X

X

X

X

X

X

X

3rd

3rd

3rd

O/D

OFF

OFF

OFF

ON

SL1 AND S4 SOLENOID MALFUNCTIONING

Driving at 3rd or O/D

Driving at 1st or 2nd

Solenoid Valve

Gear

Solenoid Valve

Gear

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

ON

OFF

ON

OFF

ON

OFF

OFF

OFF

3rd

3rd

3rd

3rd

ON

ON

OFF

ON

OFF

ON

2nd

2nd

2nd

2nd

Solenoid Valve

Gear

X

X

X

X

Solenoid Valve

Gear

SL1, SL2 AND S4 SOLENOID
MALFUNCTIONING

X

X

X

X

X

X

X

X

3rd

3rd

3rd

X

X

X

X

X

X

X

X

3rd

ON

OFF

OFF

3rd

3rd

3rd

3rd

S4

SL1

SL2

S4

SL1

SL2

S4

SL1

SL2

S4

SL1

SL2

S4

SL1

SL2

S4

SL1

SL2

S4

SL1

SL2

S4

SL1

SL2

S4

SL1

SL2

SL2 AND S4 SOLENOID
MALFUNCTIONING

–

DIAGNOSTICS

AUTOMATIC TRANSAXLE

DI–171

LEXUS RX300 (RM785E)

Fail safe function:
If either of the shift solenoid valve circuits develops an open or short, the Engine & ECT ECU turns the other
solenoid ON and OFF to shift to the gear positions shown in the table below. The Engine & ECT ECU also
turns the DSL solenoid valve OFF at the same time. If both solenoids are malfunction, hydraulic control can-
not be performed electronically and must be done manually.
Manual shifting as shown in the following table must be done (In the case of a short circuit, the Engine &
ECT ECU stops sending current to the short circuited solenoid).