Lexus RX300 (MCU15). Manual — part 199

A00328

Engine ECU

Intake Air Temp. Sensor
(Inside air flow meter)

THA

5 V

R

E1

E2

BR

L–B

22

E7

18

4

5

A10

E7

DI–28

–

DIAGNOSTICS

ENGINE

LEXUS RX300 (RM785E)

WIRING DIAGRAM

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 intake air temperature.

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.

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

Same as actual intake air 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

A00347

A00348

ON

Engine ECU

Intake Air

Temp. Sensor

4

5

Connecting

A02019

ON

Intake Air Temp. Sensor

THA

E2

Engine ECU

5 V

E1

–

DIAGNOSTICS

ENGINE

DI–29

LEXUS RX300 (RM785E)

2

Check for open in harness or engine ECU.

PREPARATION:
(a)

Disconnect the air flow meter connector.

(b)

Connect the 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 air flow meter.

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 THA and E2 of the engine
ECU connector.

HINT:
Air flow meter connector is disconnected.
Before checking, do a visual and contact pressure check for the
engine ECU connector (See page IN–32).
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 THA,
repair or replace harness.

NG

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

BE6653
A00362

A00363

ON

Intake Air

Temp. Sensor

Engine ECU

4

5

A02043

ON

Intake Air Temp. Sensor

Engine ECU

5 V

E2

THA

E6 Connector

DI–30

–

DIAGNOSTICS

ENGINE

LEXUS RX300 (RM785E)

4

Check for short in harness and engine ECU.

PREPARATION:
(a)

Disconnect the air flow meter 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 air flow meter.

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:
Air flow meter 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).

A00328

Engine ECU

E2
Water
Temp. Sensor

E7

THW

5 V

E2

E2

BR

G–W

14

E7

18

2

1

–

DIAGNOSTICS

ENGINE

DI–31

LEXUS RX300 (RM785E)

DTC

P0115

Water Temp. Circuit Malfunction

CIRCUIT DESCRIPTION

A thermistor built into the water temp. sensor changes the resistance value according to the water tempera-
ture.
The structure of the sensor and connection to the engine ECU is the same as in the DTC P0110 shown on
page DI–27.

DTC No.

DTC Detecting Condition

Trouble Area

P0115

Open or short in water temp. sensor circuit

S Open or short in water temp. sensor circuit

S Water temp. sensor

S Engine ECU

HINT:
After confirming DTC P0115 use the hand–held tester to confirm the water temperature from CURRENT
DATA.

Temperature Displayed

Malfunction

–40

°C (–40°F)

Open circuit

140C

° (284°F) or more

Short circuit

WIRING DIAGRAM

DI7OA–02