Lexus RX300 (MCU15). Service manual - part 222

DI–120

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DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

DTC

P1656

OCV Circuit Malfunction (bank 1)

DTC

P1663

OCV Circuit Malfunction (bank 2)

CIRCUIT DESCRIPTION

Refer to DTC P1349, P1354 on page DI–103.

DTC No.

DTC Detecting Condition

Trouble Area

P1656

P1663

Open or short in oil control valve circuit

S Open or short in OCV circuit

S OCV

S Engine ECU

WIRING DIAGRAM

Refer to DTC P1349, P1354 on page DI–103.

INSPECTION PROCEDURE

HINT:

S

If DTC P1656 dysplayed, check left bank OCV circuit.

S

If DTC P1663 dysplayed, check right bank OCV circuit.

S

Read freeze frame data using hand–held tester or OBD scan tool. Because freeze frame records the
engine conditions when the malfunction is detected. When troubleshooting, it is useful for determining
whether the vehicle was running or stopped, the engine was warmed up or not, the air–fuel ratio was
lean or rich, etc. at the time of the malfunction.

Hand–held tester:

1

Check OCV circuit.

PREPARATION:
(a)

Start the engine and warmed it up.

(b)

Connect the hand–held tester and select the VVT from the ACTIVE TEST menu.

CHECK:
Check the engine speed when operate the OCV by the hand–held tester.
OK:

VVT system is OFF (OCV is OFF): Normal engine speed
VVT system is ON (OCV is ON): Rough idle or engine stalled

OK

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

NG

DI6TC–02

A06076

A11891

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DIAGNOSTICS

ENGINE

DI–121

LEXUS RX300   (RM785E)

2

Check operation of OCV.

PREPARATION:
(a)

Start the engine and warmed it up.

(b)

Disconnect the OCV connector.

(c)

Apply battery positive voltage between terminals of the
OCV.

CHECK:
Check the engine speed.
OK:

Rough idle or engine stalled.

NG

Replace OCV.

OK

3

Check voltage between terminals OCV+ and OCV– of engine ECU connector 
(See page DI–103, step 3).

NG

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

OK

4

Check for open and short in harness and connector between OCV and engine
ECU (See page IN–32).

NG

Repair or replace.

OK

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

A06076

A11891

DI–122

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

OBD scan tool (excluding hand–held tester):

1

Check operation of OCV.

PREPARATION:
(a)

Start the engine and warmed it up.

(b)

Disconnect the OCV connector.

(c)

Apply battery positive voltage between terminals of the
OCV.

CHECK:
Check the engine speed.
OK:

Rough idle or engine stalled

NG

Replace OCV.

OK

2

Check voltage between terminals OCV+ and OCV– of engine ECU connector 
(See page DI–103, step 3).

NG

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

OK

3

Check for open and short in harness and connector between OCV and engine
ECU (See page IN–32).

NG

Repair or replace.

OK

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

–

DIAGNOSTICS

ENGINE

DI–123

LEXUS RX300   (RM785E)

DTC

P1780/97 Park/Neutral Position Switch Malfunction

CIRCUIT DESCRIPTION

The neutral start switch goes on when the shift lever is in the N or P shift position. When it goes on, terminal
NSW of the engnie ECU is grounded to body ground via the starter relay, thus the terminal NSW voltage
becomes 0V. When the shift lever is in the D, 2, L or R position, the neutral start switch goes off, so the voltage
of the engnie ECU. Terminal NSW becomes battery voltage, the voltage of the engnie ECU internal power
source. If the shift lever is moved from the N position to the D position, this signal is used for air–fuel ratio
correction and for idle speed control (estimated control), etc.

DTC No.

DTC Detecting Condition

Trouble Area

P1780/97

When driving under conditions (a) and (b) for 30 sec. or more

the neutral start switch is ON (N position): (2 trip detection

logic)

S Short in neutral start switch circuit

N

t l t t

it h

P1780/97

logic)

(a) Vehicle speed: 40 km/h (25 mph) or more

(b) Engine speed: 1,500 – 4,000 rpm

S Neutral start switch

S engnie ECU

HINT:
After confirming DTC P1780/97, use the hand–held tester to confirm the PNP switch signal from the CUR-
RENT DATA.

WIRING DIAGRAM

Refer to DTC P1780 on page DI–188.

INSPECTION PROCEDURE

Refer to DTC P1780 on page DI–188.

DI84H–01