Lexus RX300 (MCU15). Service manual - part 200

DI–32

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

INSPECTION PROCEDURE

HINT:

S

If DTC P0110, P0115, P0120 are output simultaneously, E2 (Sensor Ground) may be open.

S

Read freeze frame data using 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 running or stopped, the engine warmed up or not, the air–fuel ratio lean or rich, etc. at the time
of the malfunction.

1

Connect hand–held tester, and read value of water temperature.

PREPARATION:
(a)

Connect the hand–held tester to the DLC3.

(b)

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

CHECK:
Read temperature value on the hand–held tester.
OK:

Same as actual water temperature

HINT:

S

If there is open circuit, Hand–held tester indicates –40

°C (–40°F).

S

If there is short circuit, Hand–held tester indicates 140

°C (284°F) or more.

NG

–40

°C (–40°F)...Go to step 2.

140

°C (284°F) or more...Go to step 4.

OK

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

BE6653

A00365

A00366

ON

Engine ECU

2

1

Water Temp. Sensor

Connecting

A02020

ON

Water Temp. Sensor

1

2

THW

E2

Engine ECU

5 V

E1

E2

THW

–

DIAGNOSTICS

ENGINE

DI–33

LEXUS RX300   (RM785E)

2

Check for open in harness or engine ECU.

PREPARATION:
(a)

Disconnect the water temp. sensor connector.

(b)

Connect sensor wire harness terminals together.

(c)

Turn the ignition switch ON.

CHECK:
Read temperature value on the hand–held tester.
OK:

Temperature value: 140°C (284°F) or more

OK

Confirm good connection at sensor. If OK, re-
place water temp. sensor.

NG

3

Check for open in harness or engine ECU.

PREPARATION:
(a)

Remove the engine ECU with connector still connected
(See page FI–70).

(b)

Connect between terminals THW, and E2 of the engine
ECU connector.

HINT:
Water temp. sensor connector is disconnected. 
Before checking, do a visual and contact pressure check for the
engine ECU connector (See page IN–32).
(c)

Turn the ignition switch ON.

CHECK:
Read temperature value on the hand–held tester.
OK:

Temperature value: 140°C (284°F) or more

OK

Open in harness between terminals E2 or THW,
repair or replace harness.

NG

Confirm good connection at engine ECU.
If OK, check and replace engine ECU (See
page IN–32).

BE6653
A00372

A00373

ON

2

1

Engine ECU

Water Temp. Sensor

A02043

ON

Water Temp. Sensor

Engine ECU

5 V

E2

THW

E6 Connector

DI–34

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

4

Check for short in harness and engine ECU.

PREPARATION:
(a)

Disconnect the water temp. sensor connector.

(b)

Turn the ignition switch ON.

CHECK:
Read temperature value on the hand–held tester.
OK:

Temperature value: –40°C (–40°F)

OK

Replace water temp. sensor.

NG

5

Check for short in harness or engine ECU.

PREPARATION:
(a)

Remove the engine ECU with connector still connected
(See page FI–70).

(b)

Disconnect the E6 connector of the engine ECU.

HINT:
Water temp. sensor connector is disconnected.
(c)

Turn the ignition switch ON.

CHECK:
Read temperature value on the hand–held tester.
OK:

Temperature value: –40°C (–40°F)

OK

Repair or replace harness or connector.

NG

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

–

DIAGNOSTICS

ENGINE

DI–35

LEXUS RX300   (RM785E)

DTC

P0116

Water Temp. Circuit Range/Performance
Problem

CIRCUIT DESCRIPTION

Refer to DTC P0115 onpage DI-31.

DTC No.

DTC Detecting Condition

Trouble Area

If THW < –6.7

°C (20°F), 20 min. or more after starting engine,

engine coolant temp. sensor value is 35

°C (95°F) or less (2

trip detection logic)

P0116

If THW y –6.7

°C (20°F) and < 10°C (50°F), 5 min. or more

after starting engine, engine coolant temp. sensor value is

35

°C (95°F) or less (2 trip detection logic)

S Engine coolant temp. sensor

S Cooling system

If THW y 10

°C (50°F), 2 min. or more after starting engine,

engine coolant temp. sensor value is 35

°C (95°F) or less (2

trip detection logic)

INSPECTION PROCEDURE

HINT:

S

If DTC P0115 and P0116 are output simultaneously, water temp. sensor circuit may be open. Perform
troubleshooting  of DTC P0115 first.

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 warmed up or not, the air–fuel ratio lean or
rich, etc. at the time of the malfunction.

1

Are there any other codes (besides DTC P0116) being output?

YES

 Go to relevant DTC chart.

NO

2

Check thermostat (See page CO–10).

NG

Replace thermostat.

OK

Replace engine coolant temp. sensor.

DI6UZ–04