Lexus RX300 (MCU15). Service manual — part 206
DI–56
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DIAGNOSTICS
ENGINE
LEXUS RX300 (RM785E)
10
Is there DTC P0171, P0172, P0174 or P0175 being output again ?
YES
Check and replace engine ECU
(See page IN–32).
NO
11
Did vehicle run out of fuel in the past ?
NO
Check for intermittent problems
(See page DI–3).
YES
DTC P0171, P0172, P0174 or P0175 is caused by running out of fuel.
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DIAGNOSTICS
ENGINE
DI–57
LEXUS RX300 (RM785E)
DTC
P0300
Random/Multiple Cylinder Misfire Detected
DTC
P0301
Cylinder 1 Misfire Detected
DTC
P0302
Cylinder 2 Misfire Detected
DTC
P0303
Cylinder 3 Misfire Detected
DTC
P0304
Cylinder 4 Misfire Detected
DTC
P0305
Cylinder 5 Misfire Detected
DTC
P0306
Cylinder 6 Misfire Detected
CIRCUIT DESCRIPTION
Misfire: The engine ECU uses the crankshaft position sensor and camshaft position sensor to monitor
changes in the crankshaft rotation for each cylinder.
The engine ECU counts the number of times the engine speed change rate indicates that misfire has oc-
curred. And when the misfire rate equals or exceeds the count indicating that the engine condition has deteri-
orated, the check engine warning light lights up.
If the misfire rate is high enough and the driving conditions will cause catalyst overheating, the check engine
warning light blinks when misfiring occurs.
DTC No.
DTC Detecting Condition
Trouble Area
P0300
Misfiring of random cylinders is detected during any particular
200 or 1,000 revolutions
S Ignition system
S Injector
F
l
P0301
P0302
For any particular 200 revolutions for engine, misfiring is de-
tected which can cause catalyst overheating
(This causes MIL to blink) (2 trip detection logic)
S Fuel pressure
S Compression pressure
S Valve clearance
S Valve timing
P0303
Valve timing
S Air flow meter
P0303
P0304
S Air flow meter
W t
t
P0304
For any particular 1,000 revolutions of engine, misfiring is de-
S Water temp. sensor
P0305
For any articular 1,000 revolutions of engine, misfiring is de
tected which causes a deterioration in emissions
S Open or short in engine wire
0305
P0306
tected which causes a deterioration in emissions
(2 trip detection logic)
S O en or short in engine wire
S Connectorconnection
P0306
(2 trip detection logic)
S Connector connection
g
S Engine ECU
HINT:
When the 2 or more codes for a misfiring cylinder are recorded repeatedly but no random misfire code is
recorded, it indicates that the misfires were detected and recorded at different times.
DI12T–13
A14514
1
6
5
Y
L
Injector No. 1
1
1
1
2
1
L–R
B
E7
E7
E8
E8
Engine ECU
#10
#20
#30
#40
W
2
Injector No. 2
Injector No. 3
Injector No. 4
2
2
2
#50
#60
E8
3
E8
4
G
R
1
2
Injector No. 5
1
2
Injector No. 6
L–R
L–R
L–R
L–R
L–R
I7
I8
I9
I10
I11
I12
L–R
11
JH1
B
AM2
IG2
I15
Ignition Switch
L–R
Engine Room J/B
Instrument Panel J/B
1
1G
12
1G
1
1C
3
1C
W
7
6
W–L (*1)
W–R (*2)
AM2
W–R
6
2C
1
2I
F11
FL Block
1
3
Battery
(*1): LHD
(*2): RHD
DI–58
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DIAGNOSTICS
ENGINE
LEXUS RX300 (RM785E)
WIRING DIAGRAM
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DIAGNOSTICS
ENGINE
DI–59
LEXUS RX300 (RM785E)
CONFIRMATION DRIVING PATTERN
(a)
Connect the hand–held tester.
(b)
Record DTC and the freeze frame data.
(c)
Use the hand–held tester to set to Check Mode (See page DI–3).
(d)
Drive the vehicle several times with the engine speed, load and its surrounding range shown with EN-
GINE SPD, CALC LOAD in the freeze frame data or MISFIRE RPM, MISFIRE LOAD in the data list.
If you have no hand–held tester, turn the ignition switch OFF after the symptom is simulated the first time.
Then repeat the simulation process again.
HINT:
In order to memorize DTC of misfire, it is necessary to drive around MISFIRE RPM, MISFIRE LOAD in the
data list for the following period of time.
Engine Speed
Time
Idling
3 minutes 30 seconds or more
1000 rpm
3 minutes or more
2000 rpm
1 minutes 30 seconds or more
3000 rpm
1 minutes or more
(e)
Check whether there is misfire or not by monitoring DTC and the freeze frame data. After that, record
them.
(f)
Turn ignition switch OFF and least 5 seconds.
INSPECTION PROCEDURE
HINT:
S
If is the case that DTC besides misfire is memorized simultaneously, first perform the troubleshooting
for them.
S
Read freeze frame data using hand–held tester. Because freeze frame data records the engine condi-
tions 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.
S
When the vehicle is brought to the workshop and the misfire is not occurred, misfire can be confirmed
by reproducing the condition or freeze frame data. Also, after finishing the repair, confirm that there
is no misfire. (See the confirmation driving pattern)
S
When either of SHORT FT #1, LONG FT #1, SHORT FT #2 or LONG FT #2 in the freeze frame data
is besides the range of
±20 %, there is a possibility that the air–fuel ratio is inclining either to RICH
(–20 % or less) or LEAN (+20 % or more).
S
When COOLANT TEMP in the freeze frame data is less than 80
°C (176°F), there is a possibility or
misfire only during warning up.
S
In the case that misfire cannot be reproduced, the reason may be because of the driving with lack or
fuel, the use of improper fuel, a stain of ignition plug, and etc.
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