Lexus RX300 (MCU15). Service manual - part 198

BE6653
P24310

A00099

ON

1 (+)

A02017

VG

(+)

(–)

DI–24

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

2

Check voltage of air flow meter power source.

PREPARATION:
(a)

Disconnect the air flow meter connector.

(b)

Turn the ignition switch ON.

CHECK:
Measure voltage between terminal 1 of the air flow meter con-
nector and body ground.
OK:

Voltage: 9 – 14 V

NG

Check for open in harness and connector be-
tween EFI main relay (Marking: EFI) and air flow
meter (See page IN–32).

OK

3

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

PREPARATION:
(a)

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

(b)

Start the engine.

CHECK:
Measure voltage between terminal VG of the engine ECU con-
nector and body ground while engine is idling.
OK:

Voltage: 
0.5 – 3.0 V (P or N position and A/C switch OFF)

OK

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

NG

4

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

NG

Repair or replace harness or connector.

OK

A02018

E2G

–

DIAGNOSTICS

ENGINE

DI–25

LEXUS RX300   (RM785E)

Replace air flow meter.

5

Check continuity between terminal E2G of engine ECU connector and body
ground.

PREPARATION:
Remove the engine ECU with connector still connected (See
page FI–70).
CHECK:
Check continuity between terminal E2G of the engine ECU con-
nector and body ground.
OK:

Continuity (1 Ω or less)

NG

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

OK

6

Check for open in harness and connector between air flow meter and engine
ECU (See page IN–32).

NG

Repair or replace harness or connector.

OK

Replace air flow meter.

DI–26

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

DTC

P0101

Mass Air Flow Circuit Range/Performance
Problem

CIRCUIT DESCRIPTION

Refer to DTC P0100 on page DI–22.

DTC No.

DTC Detecting Condition

Trouble Area

P0101

After engine is warmed up, conditions (1), (2) and (3) continue

with more than 10 sec. engine speed 1,500 rpm or less:

(2 trip detection logic)

1. Throttle valve fully closed

2. Air flow meter output u 2.2 V

3. THW u 70 

°C (158 °F)

S Air flow meter

P0101

Conditions (1) and (2) continue with more than 10 sec. 

engine speed 2,100 rpm or more: 

(2 trip detection logic)

1. VTA y 0.63 V

2. Air flow meter output t 1.06 V

Air flow meter

INSPECTION PROCEDURE

HINT:
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 run-
ning 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 P0101) being output?

NO

Replace air flow meter.

YES

Go to relevant DTC chart (See page DI–14).

DI7O8–02

FI4741

(fig. 1)

Acceptable

Resistance k

Ω

– 20

0

20

40

60

80

100

(– 4)

32

68

104

140

176

212

30

20

10

5

3

2

1

0.5

0.3

0.2

0.1

Temp.

°C (°F)

–

DIAGNOSTICS

ENGINE

DI–27

LEXUS RX300   (RM785E)

DTC

P0110

Intake Air Temp. Circuit Malfunction

CIRCUIT DESCRIPTION

The intake air temp. sensor is built into the air flow meter and
senses the intake air temperature.
A thermistor built in the sensor changes the resistance value
according to the intake air temperature.
The lower the intake air temperature, the greater the thermistor
resistance value, and the higher the intake air temperature, the
lower the thermistor resistance value (See fig. 1).
The intake air temp. sensor is connected to the engine ECU
(See below ). The 5 V power source voltage in the engine ECU
is applied to the intake air temp. sensor from the terminal THA
(THAR) via resistor R.
That is, the resistor R and the intake air temp. sensor are con-
nected in series. When the resistance value of the intake air
temp. sensor changes in accordance with changes in the intake
air temperature, the potential at terminal THA (THAR) also
changes. Based on this signal, the engine ECU increases the
fuel injection volume to improve driveability during cold engine
operation.

DTC No.

DTC Detecting Condition

Trouble Area

P0110

Open or short in intake air temp. sensor circuit

S Open or short in intake air temp. sensor circuit

S Intake air temp. sensor (inside air flow meter)

S Engine ECU

HINT:
After confirming DTC P0110 use the hand–held tester to confirm the intake air temperature from CURRENT
DATA.

Temperature Displayed

Malfunction

–40

°C (–40°F)

Open circuit

140

°C ( 284°F ) or more

Short circuit

DI7O9–02