Lexus ES300 (1997 year). 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
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
).
(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
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
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