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.