Lexus RX300 (MCU15). Service manual - part 193

DI–4

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DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

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The diagnosis system operates in normal mode
during normal vehicle use. It also has a check mode
for technicians to simulate malfunction symptoms
and troubleshoot. Most DTCs use 2 trip detection
logic* to prevent erroneous detection, and ensure
thorough malfunction detection. By switching the
engine ECU to check mode when troubleshooting,
the technician can cause the check engine warning
light to light up for a malfunction that is only detected
once or momentarily. (hand–held tester only) (See
step 2)

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*2 trip detection logic: When a malfunction is 1st de-
tected, the malfunction is temporarily stored in the
engine ECU memory. (1st trip) If the same malfunc-
tion is detected again during the second drive test,
this 2nd detection causes the check engine warning
light to light up. (2nd trip)
(However, the IG switch must be turned OFF be-
tween the 1st trip and the 2nd trip.)

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Freeze frame data:
Freeze frame data records the engine condition
when a misfire (DTCs P0300 – P0306) or fuel trim
malfunction (DTCs P0171, P0172, P0174, P0175)
or other malfunction (first malfunction only), is de-
tected.
Because freeze frame data records the engine
conditions  (fuel system, calculated load, engine
coolant temperature, fuel trim, engine speed, ve-
hicle speed, etc.) when the malfunction is detected,
when troubleshooting it is useful for determining
whether the vehicle was running or stopped, the en-
gine warmed up or not, the air–fuel ratio lean or rich,
etc. at the time of the malfunction.

Priorities for troubleshooting:
If troubleshooting priorities for multiple DTCs are given in the
applicable DTC chart, these should be followed.
If no instructions are given troubleshoot DTCs according  to the
following priorities.

(1)

DTCs other than fuel trim malfunction (DTCs
P0171, P0172, P0174, P0175) and misfire (DTCs
P0300 – P0306).

(2)

Fuel trim malfunction (DTCs P0171, P0172, P0174,
P0175).

(3)

Misfire (DTCs P0300 – P0306).

A04550

DLC3

1 2 3 4 5 6 7 8

9 10 11 12 1314 15 16

FI2547

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DIAGNOSTICS

ENGINE

DI–5

LEXUS RX300   (RM785E)

(b)

Check the DLC3.
The vehicle’s engine ECU uses the ISO 9141–2 commu-
nication protocol. The terminal arrangement of DLC3
complies with ISO 15031–03 and matches the ISO
9141–2 format.

Terminal No.

Connection / Voltage or Resistance

Condition

7

Bus ę Line / Pulse generation

During transmission

4

Chassis Ground / ↔ Body Ground 1 Ω or less

Always

16

Battery Positive / ↔ Body Ground 9 – 14 V

Always

HINT:
If your display shows ”UNABLE TO CONNECT TO VEHICLE”
when you have connected the cable of the OBD scan tool or
hand–held tester to DLC3, turned the ignition switch ON and
operated the hand–held tester, there is a problem on the vehicle
side or tool side.

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If communication is normal when the tool is connected to
another vehicle, inspect DLC3 on the original vehicle.

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If communication is still not possible is when the tool is
connected to another vehicle, the problem is probably in
the tool itself, so consult the Service Debarment listed in
the tool,s instruction manual.

2.

INSPECT DIAGNOSIS (Normal Mode)

(a)

Check the check engine warning light.
(1)

The check engine warning (CHK ENG) comes on
when the ignition switch is turned ON and the en-
gine is not running.

HINT:
If the check engine warning (CHK ENG) does not light up, trou-
bleshoot the combination meter.

(2)

When the engine is started, the check engine warn-
ing light should go off. If the lamp remains on, the
diagnosis system has detected a malfunction or ab-
normality in the system

(b)

Check the DTC, using hand–held tester.

NOTICE:
Hand–held tester only: 
When the diagnosis system is switched from normal mode
to check (test) mode, it erases all DTCs and freezed frame
data recorded in normal mode. So before switching modes,
always check the DTCs and freezed frame data, and note
them down.

DI–6

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DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

(1)

Prepare the hand–held tester.

(2)

Connect the hand–held tester to DLC3.

(3)

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

(4)

Use the hand–held tester to check the DTCs and
freezed frame data; note them down. (For operating
instructions, see the hand–held tester,s instruction
book.)

(5)

See page DI–14 to confirm the details of the DTCs.

(c)

Clear the DTC.
The following actions will erase the DTCs and freezed
frame data.

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Operating the hand–held tester to erase the
codes. (See the hand–held tester’s instruc-
tion book for operating instructions.)

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Disconnecting the battery terminals or EFI
fuse.

NOTICE:
If the hand–held tester switches the engine ECU from nor-
mal mode to check mode or vice–versa, or if the  ignition
switch is turned from ON to ACC or OFF during check
mode, the DTCs and freezed frame data will be erased.

3.

INSPECT DIAGNOSIS (Check (Test) Mode)

HINT:
Hand–held tester only:
Compared to the normal mode, the check mode has an in-
creased sensitivity to detect malfunctions.
Furthermore, the same diagnostic items which are detected in
the normal mode can also be detected in the check (test) mode.
(a)

Check the DTC.
(1)

Initial conditions

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Battery positive voltage 11V or more.

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Throttle valve fully closed.

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Transmission in ”P” or ”N” position.

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Air conditioning switched OFF.

(2)

Turn ignition switch OFF.

(3)

Prepare the hand–held tester.

(4)

Connect the hand–held tester to DLC3 on the at the
lower left of the instrument panel.

(5)

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

FI3605

ON

OFF

Flashing

0.13 Second

N09348

Interface Box

Vehicle Harness

Engine
ECU

Break–Out–Box

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DIAGNOSTICS

ENGINE

DI–7

LEXUS RX300   (RM785E)

(6)

Switch the hand–held tester normal mode to check
(test) mode. (Check that the check engine warning
light (CHK ENG) flashes.) 

(7)

Start the engine. (The check engine warning (CHK
ENG) light goes out after the engine start.)

(8)

Simulate the conditions of the malfunction de-
scribed by the customer.

NOTICE:
Leave the ignition switch ON until you have checked the
DTC, etc.

(9)

After simulating the malfunction conditions, use the
hand–held tester diagnosis selector to check the
DTCs and freezed frame data, etc.

HINT:
Take care not to turn the ignition switch OFF. Turning the ignition
switch OFF switches the diagnosis system from check (test)
mode to normal mode. so all DTCs, etc. are erased.

(10) After checking the DTCs, inspect the applicable cir-

cuit.

(b)

Using break–out–box and hand–held tester
(1)

Hook up the break–out–box and hand–held tester
to the vehicle.

(2)

Read the engine ECU input/output values following
the prompts on the tester screen.

HINT:
Hand–held tester has a ”Snapshot” function. This records the
measured values and is effective in the diagnosis of intermittent
problems. Please refer to the hand–held tester/break–out–box
operator,s manual for further details.

4.

FAIL–SAFE CHART

If any of the following codes is recorded, the engine ECU enters fail–safe mode.

DTC No.

Fail–Safe Operation

Fail–Safe Deactivation Conditions

P0100

S Ignition timing fixed at 10

° BTDC

Returned to normal condition

P0110

Intake air temp. is fixed at 20

°C (68°F)

Returned to normal condition

P0115

Water temp. is fixed at 80

°(176°F)

Returned to normal condition

P0120

VTA is fixed at 0

°

The following condition must be repeated at least 2 times

consecutively

When closed throttle position switch is ON: 

0.1 V x VTA and 0.95 V

P0325

P0300

Max. timing retardation

IG switch OFF

P0500

High RPM for cut is prohibited

ISC control prohibited

Returned to normal condition

P1300

P1305

P1310

P1315

Fuel cut

Feturned to normal condition