Lexus SC300 / Lexus SC400. Service manual — part 338

EXHAUST GAS RECIRCULATION (EGR) SYSTEM

DESCRIPTION

To reduce NOx emission, part of the exhaust gases are recirculated through the EGR valve to the intake man-

ifold to lower the maximum combustion temperature.

OPERATION

To reduce NOx emission, part of the exhaust gases are recirculated through the EGR valve to the intake manifold to lower the
maximum combustion temperature.

Coolant

Temp.

VSV

Throttle Valve

Opening

Pressure in the EGR Valve

Pressure Chamber

EGR Vacuum

Modulator

EGR

Valve

Exhaust Gas

Below 45

C

OPEN

CLOSED

Not recircu-

(113

F)

OPEN

–

–

–

CLOSED

lated

Positioned be-

low EGR port

–

–

CLOSED

Not recircula-

ted

Above 50

°

C

(122

°

F)

CLOSED

Positioned be-

tween EGR port

(1)

LOW

* Pressure constantly

alternating between

OPENS passage

to atmosphere

CLOSED

Not recircula-

ted

tween EGR port

and R port

(2)

HIGH

alternating between

low and high

OPENS passage

to atmosphere

OPEN

Recirculated

Above 50

°

C

(122

°

F)

CLOSED

Positioned

above R port

(3)

HIGH

**

CLOSES passage

to atmosphere

OPEN

Recirculated

(increase)

*

Pressure increases

Modulator closes

EGR valve opens

Pressure drops

EGR Valve closes

Modulator opens

**

When the throttle valve is positioned above the R port, the EGR vacuum modulator will close the atmosphere passage and

open the EGR valve to increase the EGR gas, even if the exhaust pressure is insufficiently low.

–

EMISSION CONTROL SYSTEMS

Exhaust Gas Recirculation (EGR) System

EC–11

INSPECTION OF EGR SYSTEM

1. CHECK AND CLEAN FILTER IN EGR VACUUM

MODULATOR
(a) Remove the cap and filter.
(b) Check the filter for contamination or damage.
(c) Using compressed air, clean the filter.
(d) Reinstall the filter and cap.
HINT: Install the filter with the coarser surface facing the at-
mospheric side (out ward).

2.

INSPECT SYSTEM OPERATION
(a) Connect the tachometer to terminal IG – of the check

(”DIAGNOSIS”) connector.

(b) Using SST connect the terminals TE1 and E1 of the

check (”DIAGNOSIS”) connector.

SST 09843–18020

(c) Keep the engine at 3,500 rpm with the transmission in

”N” position.

(d) Remove the SST from the check connector.
SST 09843–18020

EC–12

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EMISSION CONTROL SYSTEMS

Exhaust Gas Recirculation (EGR) System

(e) Check whether the engine rpm increases 100–300 rpm

under the following conditions:

Coolant temp.

Below 45

°

C (113

°

F) . . . NO increase

Above 50

°

C (122

°

F) . . . Increases

INSPECTION OF VSV

1. REMOVE

VSV

(a) Disconnect the VSV connector.
(b) Disconnect the two vacuum hoses from VSV.
(c) Remove the bolt and VSV from the intake manifold.

2. INSPECT

VSV

(a) Inspect VSV for open circuit.

Using an ohmmeter, check that there is continuity be-
tween the terminals.

Resistance (Cold): 33–39

If there is no continuity, replace the VSV.

(b) Inspect VSV for ground.

Using an ohmmeter, check that there is no continuity be-
tween each terminal and the body.

If there is continuity, replace the VSV.

(c) Inspect VSV operation:

1) Check that the air flows from ports E to G

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EMISSION CONTROL SYSTEMS

Exhaust Gas Recirculation (EGR) System

EC–13

2) Apply battery voltage across the terminals
3) Check that the air flows from port E to port G

If operation is not as specified, replace the VSV.

3. REINSTALL

VSV

(a) Install the VSV with the nut.

Torque: 18 N

⋅

m (185 kgf

⋅

cm, 13 ft

⋅

lbf)

(b) Connect the following hoses:

(1) Vacuum hose (from throttle body)
(2) Vacuum hose (from EGR vacuum modulator)

(c) Connect the VSV connector.

INSPECTION OF EGR VACUUM
MODULATOR

1. DISCONNECT VACUUM HOSES FROM EGR VACUUM

MODULATOR
Disconnect the three vacuum hoses from ports P, Q and R of
the EGR vacuum modulator.

2.

INSPECT EGR VACUUM MODULATOR OPERATION
(a) Block ports P and R with your finger.
(b) Blow air into port Q, and check that the air passes

through to the air filter side freely.

(c) Start the engine, and maintain speed at 2,500 rpm.
(d) Repeat the above test. Check the there is a strong

resistance to air flow.

3. RECONNECT

VACUUM

HOSES

TO

EGR

VACUUM

MODULATOR
Connect the three vacuum hoses to the proper locations.

EC–14

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EMISSION CONTROL SYSTEMS

Exhaust Gas Recirculation (EGR) System