Lexus ES300 (1997 year). Service manual — part 313

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

°

)

DI–28

–

DIAGNOSTICS

ENGINE

180

1997 LEXUS ES300 (RM511U)

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 temperature sensor is connected to the ECM. The 5 V power source voltage in the ECM is
applied to the intake air temperature sensor from the terminal THA via resistor R.
That is, the resistor R and the intake air temperature sensor are connected in series. When the resistance
value of the intake air temperature sensor changes in accordance with changes in the intake air temperature,
the potential at terminal THA also changes. Based on this signal, the ECM increases the fuel injection vol-
ume to improve driveability during cold engine operation.
If the ECM detects the DTC ”P0110”, it operates the fail–safe function in which the intake air temperature
is assumed to be 20

°

C (68

°

F).

<Reference>

Intake air temp.

°

C (

°

F)

Resistance

(k

Ω

)

Voltage

(V)

–20 (–4)

16.0

4.3

0 (32)

5.9

3.4

20 (68)

2.5

2.4

40 (104)

1.1

1.4

60 (140)

0.6

0.9

80 (176)

0.3

0.5

100 (212)

0.1

0.2

DI09D–01

FI6448

Intake Air Temp. Sensor

(Inside the mass air flow meter)

ECM

5V

THA

E2

E1

E9

E9

21

22

1

2

R

L–Y

BR

–

DIAGNOSTICS

ENGINE

DI–29

181

1997 LEXUS ES300 (RM511U)

DTC No.

DTC Detecting Condition

Trouble Area

P0110

Open or short in intake air temp. sensor circuit

Open or short in intake air temp. sensor circuit

Intake air temp. sensor

ECM

HINT:After confirming DTC P0110 use the OBD II scan tool or LEXUS hand–held tester to confirm the intake
air temp. form ”CURRENT DATA”.

Temp. Displayed

Malfunction

–40

°

C ( –40

°F

)

Open circuit

140

°

C ( 284

°F

) or more

Short circuit

WIRING DIAGRAM

A00210

ON

Intake Air
Temp. Sensor

ECM

5V

E2

THA

21

22

3

4

E9

E9

BE6653
FI7055

DI–30

–

DIAGNOSTICS

ENGINE

182

1997 LEXUS ES300 (RM511U)

INSPECTION PROCEDURE

HINT:If DTC P0110 (Intake Air Temp. Circuit Malfunction), P0115 (Engine Coolant Temp. Circuit Malfunc-
tion), P0120 (Throttle/Pedal Position Sensor/Switch ”A” Circuit Malfunction) and P1410 (EGR Valve Position
Sensor Circuit Malfunction) are output simultaneously, E2 (Sensor Ground) may be open.

1

Connect OBD II scan tool or LEXUS hand–held tester, and read value of
intake air temp.

PREPARATION:
(a)

Connect the OBD II scan tool or LEXUS hand–held tester to the DLC3.

(b)

Turn ignition switch ON and push the OBD II scan tool or LEXUS hand–held tester main switch ON.

CHECK:
Read temp. value on the OBD II scan tool or LEXUS hand–held tester.
OK:

Same as actual intake air temp.

HINT:

If there is open circuit, OBD II scan tool or LEXUS hand–held tester indicates –40

°C (−40°F).

If there is short circuit, OBD II scan tool or LEXUS 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

).

2

Check for open in harness or ECM.

PREPARATION:
(a)

Disconnect the mass air flow meter connector.

(b)

Connect sensor wire harness terminals together.

(c)

Turn ignition switch ON.

CHECK:
Read temp. value on the OBD II scan tool or LEXUS
hand–held tester.
OK:

Temp. value: 140

°

C (284

°

F) or more

OK

Confirm good connection at sensor.
If OK, replace mass air flow meter.

NG

A00211

ON

Intake Air
Temp. Sensor

ECM

5V

E2

21

22

E9

E9

BE6653
FI7057
P23860

E2

THA

THA

A00212

ON

Intake Air
Temp. Sensor

ECM

5V

E2

21

22

THA

BE6653
FI7054

E9

E9

–

DIAGNOSTICS

ENGINE

DI–31

183

1997 LEXUS ES300 (RM511U)

3

Check for open in harness or ECM.

PREPARATION:
(a)

Remove the glove compartment (See page

SF–64

).

(b)

Connect between terminals THA and E2 of ECM connec-
tor.

HINT:Mass air flow meter connector is disconnected.
Before checking, do a visual and contact pressure check for the
ECM connector (See page

IN–27

).

CHECK:
Read temp. value on the OBD II scan tool or LEXUS hand–held
tester.
OK:

Temp. value: 140

°

C (284

°

F) or more

OK

Open in harness between terminal E2 or THA,
repair or replace harness.

NG

Confirm good connection at ECM.
If OK, check and replace ECM.

4

Check for short in harness and ECM.

PREPARATION:
(a)

Disconnect the mass air flow meter connector.

(b)

Turn ignition switch ON.

CHECK:
Read temp. value on the OBD II scan tool or LEXUS hand–held
tester.
OK:

Temp. value: –40

°

C (–40

°

F)

OK

Replace mass air flow meter.

NG