Lexus RX300 (MCU15). Service manual — part 197

DI–20

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DIAGNOSTICS

ENGINE

LEXUS RX300 (RM785E)

IG switch ON

4.5 – 5.5

IGF (E8–25) – E1 (E7–17)

B ↔ BR

Idling

Pulse generation

(See page DI–96)

VV1+ (E8–10)

– NE– (E8–24)

O ↔ W

Idling

Pulse generation

(See page DI–67)

NE+ (E8–16) – NE– (E8–24)

B ↔ W

Idling

Pulse generation

(See page DI–67)

ACIS (E8–17) – E01 (E8–21)

R–Y ↔ W–B

IG

it h ON

9

14

ACI1 (E7–15) – E01 (E8–21)

LG ↔ W–B

IG switch ON

9 – 14

FC (E9 3)

E01 (E8 21)

L Y

W B

IG switch ON

9 – 14

FC (E9–3) – E01 (E8–21)

L–Y ↔ W–B

Idling

0 – 3.0

EVP1 (E7–7) – E01 (E8–21)

W–L ↔ W–B

IG switch ON

9 – 14

RSO (E8–26) – E01 (E8–21)

Y–R ↔ W–B

IG switch ON, Disconnect E17 connector from engine ECU

9 – 14

OXS (E10–8) – E1 (E7–17)

W ↔ BR

Maintain engine speed at 2,500 rpm for 3 min. after warming up

Pulse generation

(See page DI–71)

HTS (E10 9)

E03 (E8 30)

B ↔ W B

Idling

9 – 14

HTS (E10–9) – E03 (E8–30)

B ↔ W–B

IG switch ON

Below 3.0

KNKR (E8–27) – E1 (E7–17)

W ↔ BR

Idling

Pulse generation

KNKL (E8–28) – E1 (E7–17)

B ↔ BR

Idling

Pulse generation

(See page DI–63)

NSW (E10 20)

E1 (E7 17)

B W ↔ BR

IG switch ON, Other shift position in P, N

9 – 14

NSW (E10–20) – E1 (E7–17)

B–W ↔ BR

IG switch ON, Shift position in P, N

0 – 3.0

SPD (E10–22) – E1 (E7–17)

V–W ↔ BR

IG switch ON,.Rotate driving wheel slowly

0 – 5

TC (E10–5) – E1 (E7–17)

P–B ↔ BR

IG switch ON

9 –14

W (E9–6) – E01 (E8–21)

Y–G ↔ W–B

IG switch ON

Below 3.0

PS (E7–9) – E1 (E7–17)

B–Y ↔ BR

IG switch ON

9 – 14

CF (E10 26)

E1 (E7 17)

R W ↔ BR

Electric cooling fan is operating on high speed

9 – 14

CF (E10–26) – E1 (E7–17)

R–W ↔ BR

Electric cooling fan is operating on low speed or OFF

0– 2

TACH (E10–27) – E1 (E7–17)

O ↔ BR

Idling

Pulse generation

SIL (E9–4) – E1 (E7–17)

W ↔ BR

During transmission

Pulse generation

STP (E9 15)

E1 (E7 17)

G O ↔ BR

IG switch ON, Brake pedal depressed

7.5 – 14

STP (E9–15) – E1 (E7–17)

G–O ↔ BR

IG switch ON, Brake pedal released

Below 1.5

AFR+ (E7–11)– E1 (E7–17)

R ↔ BR

IG switch ON

3 3

AFL+ (E7–12) – E1 (E7–17)

L ↔ BR

IG switch ON

3.3

AFR– (E7–20) – E1 (E7–17)

G ↔ BR

IG switch ON

3 0

AFL– (E7–21)– E1 (E7–17)

B–W ↔ BR

IG switch ON

3.0

HAFR (E7 3)

E04 (E7 1)

L ↔ W B

IG switch ON

Below 3.0

HAFR (E7–3) – E04 (E7–1)

L ↔ W–B

Idling (warm up engine)

Pulse generation

HAFL (E7 4)

E05 (E7 8)

G ↔ W B

IG switch ON

Below 3.0

HAFL (E7–4) – E05 (E7–8)

G ↔ W–B

Idling (warm up engine)

Pulse generation

KSW (E10 23)

E1 (E7 17)

L ↔ BR

At time of inserting the key

Below 1.5

KSW (E10–23) – E1 (E7–17)

L ↔ BR

In condition without the key inserted

4 – 5

RXCK (E10–19) – E1 (E7–17)

P ↔ BR

At time of inserting the key

Pulse generation

CODE (E10–28) – E1 (E7–17)

V ↔ BR

At time of inserting the key

Pulse generation

IGSW (E9–2) – E1 (E7–17)

B–O ↔ BR

IG switch ON

9 – 14

TXCT (E10–18) – E1 (E7–17)

GR ↔ BR

At time of inserting the key

Pulse

IMLO (E9–22) – E1 (E7–17)

L ↔ BR

In condition without the key inserted

Pulse

MREL (E9–8) – E1 (E7–17)

B–W ↔ BR

IG switch ON

9 – 14

DI1IA–24

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DIAGNOSTICS

ENGINE

DI–21

LEXUS RX300 (RM785E)

PROBLEM SYMPTOMS TABLE

Symptom

Suspect Area

See page

Engine does not crank (Does not start)

1. Starter and starter relay

2. Neutral start switch circuit

ST–2

ST–20

DI–140

No initial combustion (Does not start)

1. Engine immobiliser system

2. ECU power source circuit

3. Fuel pump control circuit

BE–2

DI–124

DI–128

No complete combustion (Does not start)

1. Fuel pump control circuit

DI–128

Under normal condition (Difficult to start)

1. Fuel pump control circuit

2. Compression

DI–128

EM–3

Cold engine (Difficult to start)

1. Fuel pump control circuit

DI–128

Hot engine (Difficult to start)

1. Fuel pump control circuit

DI–128

High engine idle speed (Poor idling)

1. A/C signal circuit (Compressor circuit)

2. ECU power source circuit

–

DI–124

Low engine idle speed (Poor idling)

1. A/C signal circuit (Compressor circuit)

2. Fuel pump control circuit

–

DI–128

Rough idling (Poor idling)

1. Compression

2. Fuel pump control circuit

EM–3

DI–128

Hunting (Poor idling)

1. ECU power source circuit

2. Fuel pump control circuit

DI–124

DI–128

Hesitation/Poor acceleration (Poor driveability)

1. Fuel pump control circuit

DI–128

Surging (Poor driveability)

1. Fuel pump control circuit

DI–128

Soon after starting (Engine stall)

1. Engine immobiliser system

2. Fuel pump control circuit

BE–2

DI–128

During A/C operation (Engine stall)

1. A/C signal circuit (Compressor circuit)

2. Engine ECU

–

IN–22

DI7O7–02

FI6929
A09074

A09707

Power Transistor

Platinum Hot Wire

Output

Voltage

Temparature
sensor

A

B

Platinum Hot Wire

Temparature
sensor

B+

DI–22

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DIAGNOSTICS

ENGINE

LEXUS RX300 (RM785E)

CIRCUIT INSPECTION

DTC

P0100

Mass Air Flow Circuit Malfunction

CIRCUIT DESCRIPTION

The air flow meter uses a platinum hot wire. The hot wire air flow meter consists of a platinum hot wire, tempa-
rature sensor and a control circuit installed in a plastic housing. The hot wire air flow meter works on the
principle that the hot wire and temparature sensor located in the intake air bypass of the housing detect any
changes in the intake air temperature.
The hot wire is maintained at the set temperature by controlling the current flow through the hot wire. This
current flow is then measured as the output voltage of the air flow meter.
The circuit is constructed so that the platinum hot wire and temparature sensor provide a bridge circuit, with
the power transistor controlled so that the potential of A and B remains equal to maintain the set temperature.

DTC No.

DTC Detecting Condition

Trouble Area

P0100

Open or short in air flow meter circuit with more than 3 sec.

engine speed less than 4,000 rpm

S Open or short in air flow meter circuit

S Air flow meter

S Engine ECU

HINT:
After confirming DTC P0100 use the hand–held tester to confirm the air flow ratio from CURRENT DATA.

Air Flow Value (gm/sec.)

Malfunction

Approx. 0.0

S Air flow meter power source circuit open

S VG circuit open or short

271.0 or more

S EVG circuit open

A14512

Engine ECU

E2G

VG

MREL

25

10

19

E9

E7

E7

Air Flow Meter

1

A10

3

2

EFI

EFI Relay

Engine Room J/B

Battery

FL Block

J/C

ED

B–G

W

A

B–R

J2

W–B

W

B–W

2

5

1

3

2I

5

1

4

3

2F

2B

2D

3

1

Y–B

G–B

F11

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DIAGNOSTICS

ENGINE

DI–23

LEXUS RX300 (RM785E)

WIRING DIAGRAM

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.

1

Connect hand–held tester, and read value of air flow rate.

PREPARATION:
(a)

Connect the hand–held tester to the DLC3.

(b)

Turn the ignition switch ON and push the hand–held tester main switch ON.

(c)

Start the engine.

CHECK:
Read air flow rate on the hand–held tester.
RESULT:

Type I

Type II

Air flow rata (gm/sec.)

0.0

271.0 or more

Type I

Go to step 2.

Type II

Go to step 5.