Lexus RX300 (MCU15). Service manual - part 212

P01559

Throttle Valve

To Cylinder

Signal

From     
Air
Cleaner

Valve

ISC Valve

Intake Air
Chamber

Engine
ECU

DI–80

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

DTC

P0505

Idle Control System Malfunction

CIRCUIT DESCRIPTION

The rotary solenoid type ISC valve is located in front of the in-
take air chamber and intake air bypassing the throttle valve is
directed to the ISC valve through a passage.
In this way the intake air volume bypassing the throttle valve is
regulated, controlling the engine speed.
The engine ECU operates only the ISC valve to perform idle–up
and provide feedback for the target idling speed.

DTC No.

DTC Detecting Condition

Trouble AreaTrouble Area

P0505

Idle speed continues to differ greatly from the target speed

(2 trip detection logic)

S ISC valve is stuck or closed

S Open or short in ISC valve circuit

S Open or short in A/C switch circuit

S Air induction system

S Engine ECU

DI84E–01

A14517

Engine Room J/B

EFI Relay

Engine ECU

EFI

Battery

RSO

E01

26

E9

21

E8

B–R

ED

3

5

1

J2
J/C

2F

2D

2B

5

2

4

3

EC

1

1

3

A

W

E8

MREL

8

W–B

W–B

3

2

F11
Fusible Link Block

EB

I13
ISC Valve

2I

1

W–B

W

B–W

Y–R

–

DIAGNOSTICS

ENGINE

DI–81

LEXUS RX300   (RM785E)

WIRING DIAGRAM

INSPECTION PROCEDURE

HINT:
Read freeze frame data using a hand–held tester. Because freeze frame records the engine conditions when
the malfunction is detected, when troubleshooting it is useful for determining whether the vehicle was run-
ning or stopped, the engine warmed up or not, the air–fuel ratio lean or rich, etc. at the time of the malfunction.

Hand–held tester:

1

Check operation of the ISC valve.

PREPARATION:
(a)

Connect the hand–held tester to the DLC3.

(b)

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

(c)

Select the active test mode on the hand–held tester.

CHECK:
Check the engine speed when the ISC valve operated by the hand–held tester.
OK:

Engine speed is increased and decreased in response to change of ISC duty ratio.

A07628

ON

RSO

Connector

E7

(+)

(–)

DI–82

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

OK

Check for intermittent problems
(See page DI–3).

NG

2

Check voltage between terminals RSO of engine ECU connector and body
ground.

PREPARATION:
(a)

Remove the engine ECU with the connector still con-
nected (See page FI–70).

(b)

Disconnect the E7 connector of the engine ECU.

(c)

Turn the ignition switch ON.

CHECK:
Measure the voltage between terminals RSO of the engine
ECU connector and body ground,
OK:

Voltage: 9 – 14 V

OK

Go to step 4.

NG

3

Check ISC valve (See page FI–48).

NG

Replace ISC valve.

OK

Check for open and short in harness and connector between engine room J/B and ISC valve and
engine ECU (See page IN–32).

4

Check operation of the ISC valve (See page FI–44).

NG

Repair or replace ISC valve.

OK

A07628

ON

RSO

Connector

E7

(+)

(–)

–

DIAGNOSTICS

ENGINE

DI–83

LEXUS RX300   (RM785E)

5

Check the blockage of ISC valve and the passage to bypass the throttle valve.

NG

Repair or replace ISC valve.

OK

Check and replace engine ECU 
(See page IN–32).

OBD scan tool (excluding hand–held tester):

1

Check voltage between terminals RSO of engine ECU connector and body
ground.

PREPARATION:
(a)

Remove the engine ECU with the connector still con-
nected (See page FI–70).

(b)

Disconnect the E7 connector of the engine ECU.

(c)

Turn the ignition switch ON.

CHECK:
Measure the voltage between terminals RSO of the engine
ECU connector and body ground.
OK:

Voltage: 9 – 14 V

OK

Go to step 3.

NG

2

Check ISC valve (See page FI–48).

NG

Replace ISC valve.

OK

Check for open and short in harness and connector between engine room J/B and ISC valve and
engine ECU (See page IN–32).