Lexus RX300 (MCU15). Manual — part 202
A02021
ON
VTA1 (+) E2 (–)
A02022
ON
E2 (–)
VC (+)
DI–40
–
DIAGNOSTICS
ENGINE
LEXUS RX300 (RM785E)
When not using hand–held tester:
1
Check voltage between terminals VTA1 and E2 of engine ECU
PREPARATION:
(a)
Remove the engine ECU with connector still connected
(See page FI–70).
(b)
Turn the ignition switch ON.
CHECK:
Measure voltage between terminals VTA1 and E2 of the engine
ECU connector.
OK:
Throttle valve
Voltage
Fully closed
0.3 – 1.0 V
Fully open
2.7 – 5.2 V
NG
Check and replace engine ECU (See page
IN–32).
OK
Check for open and short in harness and connector between engine ECU and throttle position
sensor (VTA line) (See page IN–32).
2
Check voltage between terminals VC and E2 of engine ECU connector.
PREPARATION:
(a)
Remove the engine ECU with connector still connected
(See page FI–70).
(b)
Turn the ignition switch ON.
CHECK:
Measure voltage between terminals VC and E2 of the engine
ECU connector.
OK:
Voltage: 4.5 – 5.5 V
NG
Check and replace engine ECU (See page
IN–32).
OK
Check for open in harness and connector be-
tween engine ECU and sensor (VC line) (See
page IN–32).
–
DIAGNOSTICS
ENGINE
DI–41
LEXUS RX300 (RM785E)
DTC
P0121
Throttle/Pedal Position Sensor/Switch ”A”
Circuit Range/Performance Problem
CIRCUIT DESCRIPTION
Refer to DTC P0120 onpage DI-36.
DTC No.
DTC Detecting Condition
Trouble Area
P0121
While vehicle speed drops from 30 km/h (19 mph) or more to 0
km/h (0 mph), output value of throttle position sensor is out of
applicable range. (2 trip detection logic)
S Throttle position sensor
S Engine ECU
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.
Replace throttle body (See page FI–33).
DI1LI–10
A00477
Cover
Atmosphere
Platinum
Electrode
Solid Electrolyte
(Zirconia Element)
Platinum
Electrode
Heater
Coating (Ceramic)
Exhaust Gas
(V)
4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.6
17
Air–Fuel Ratio
2.4
16
15
12
14
13
19
18
engine
ECU
Monitored
A/F
Sensor V
oltage
DI–42
–
DIAGNOSTICS
ENGINE
LEXUS RX300 (RM785E)
DTC
P0125
Insufficient Coolant Temp. for Closed Loop
Fuel Control
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three–way
catalytic converter is used. For the most efficient use of the three–way catalytic converter, the air–fuel ratio
must be precisely controlled so that it is always close to the stoichiometric air–fuel ratio.
The A/F sensor has the characteristic that provides output voltage
*
approximately proportional to the existing
air–fuel ratio. The A/F sensor output voltage
*
is used to provide feedback for the engine ECU to control the
air–fuel ratio.
By the A/F sensor output, the engine ECU can determine the deviation amount from the stoichiometric air–
fuel ratio and control the proper injection time immediately. If the A/F sensor is malfunctioning, the engine
ECU is unable to perform accurate air–fuel ratio control.
The A/F sensor is equipped with a heater which heats the zirconia element. The heater is controlled by the
engine ECU. When the intake air volume is low (the temp. of the exhaust gas is low), current flows to the
heater to heat the sensor for accurate oxygen concentration detection.
*: The voltage value changes at the inside of the engine ECU only.
DTC No.
DTC Detecting Condition
Trouble Area
P0125
After engine is warmed up, A/F sensor output* does not
change when conditions (a), (b) and (c) continue for at least
1.5 min.
*: Output value changes at inside of engine ECU only.
(a) Engine speed: 1,500 rpm or more
(b) Vehicle speed: 40 ∼ 100 km/h (25 ∼ 62 mph)
(c) Throttle valve does not fully closed
(d) After starting engine y 140 sec
S Fuel system
S Injector
S Ignition system
S Gas leakage on exhaust system
S Open or short in A/F sensor circuit (bank 1, 2 sensor 1)
S A/F sensors (bank 1, 2 sensor 1)
S Engine ECU
DI7J3–03
A14513
Engine ECU
MREL
E9
W–B
2
3
4
B–W
8
W
19
B
2
4
EC
A
B–R
Battery
EFI Relay
1
2
3
5
1A
2G
8
2I
A/F HEATER Relay
Engine Room J/B
H12
Oxygen Sensor
(Bank 1 Sensor 2)
A
5
2B
2G
2F
2
2
2
2
5
EFI
B–R
A
B–R
J10
J/C
2
2
2
C
3
1
1
2
4
ED
(Bank 2 Sensor 1)
A12 A/F Sensor
(Bank 1 Sensor 1)
A11 A/F Sensor
HTS
OXS
HAFR
AFR+
AFR–
HAFL
AFL+
AFL–
E10
E10
E7
E7
E7
E7
E7
E7
2B
W–B
B–R
J2
J/C
W
W
B–W
FL Block
A/F HTR
5
1
2
1
3
4
3
A
J/C
IA2
15
9
B
B
1
4
2
B–R
J3
J4
W
W
IA2
7
BR
IA2
EB1
3
1
4
2
4
3
1
2
B–R
L
R
G
BR
B–R
EB1
2
11
20
12
21
8
IH1
G
L
B–W
BR
BR–W
F11
R/B No. 2
+B
MT
E7
OX
W–B
–
DIAGNOSTICS
ENGINE
DI–43
LEXUS RX300 (RM785E)
HINT:
S
After confirming DTC P0125, use a hand-held tester to confirm voltage output of heated oxygen senĆ
sors (bank 1, 2 sensor 1) from CURRENT DATA.
S
The engine ECU controls the voltage of AFL+, AFR+ and AFL–, AFR– terminals of engine ECU to the
fixed voltage. Therefore, it is impossible to confirm the A/F sensor output voltage without a hand–held
tester.
WIRING DIAGRAM
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