Lexus SC300 / Lexus SC400. Service manual - part 881

–MEMO–

ENGINE TROUBLESHOOTING

TR–107

Diag. Code 71

EGR System Malfunction (Only for
USA spec.)

CIRCUIT DESCRIPTION

If even one of the following conditions is ful-
filled, the VSV is turned ON by a signal from
the ECU. This results in atmospheric air act-
ing on the EGR valve, closing the EGR valve
and shutting off the exhaust gas (EGR cut–
OFF).

•

Coolant temp. below 50

°

C (122

°

F)

•

During deceleration (throttle valve closed)

•

Light engine load (amount of intake air very
  small).

•

Engine speed over 5,200 rpm.

The EGR system is designed to recirculate the exhaust gas properly controlled according to the driv-
ing condition back into the intake air–fuel mixture. It helps to slow down combustion in the cylinder
and thus lower the combustion temperature which, in turn, reduces the amount of NOx emission. The
amount of EGR is regulated by the EGR vacuum modulator according to the engine load.

Code No.

Diagnostic Code Detecting Condition

Trouble Area

EGR

t

i 70

°

C (158

°

F)

b l

f

1 4

•

Open in EGR gas temp. sensor circuit.

EGR gas temp. is 70

°

C (158

°

F) or below for 1  4

min. under conditions (a) and (b).

(2 trip detection logic)*

O en in EGR gas tem . sensor circuit.

•

Short in VSV circuit for EGR.

71

      (2 trip detection logic)*
      (a) Coolant temp.: 63

°

C (145

°

F) or more.

(b) EGR operation possible (EX ECT in 3rd speed

Short in VSV circuit for EGR.

•

EGR hose disconnected, valve stuck.

     (b) EGR operation possible (EX. ECT in 3rd speed
            (5th for  M/T), A/C ON, 60 mph (96 km/h), Flat

road)

EGR hose disconnected, valve stuck.

•

Clogged EGR gas passage.

            road).

gg

g

g

•

ECU

*: See page 

TR–25

.

TR–104

–

ENGINE TROUBLESHOOTING

Circuit Inspection

CIRCUIT DESCRIPTION (Cont’d)
DIAGNOSIS TROUBLE CODE DETECTION DRIVING PATTERN

Purpose of the driving pattern.
(a)  To simulate diag. trouble code detecting condition after diag. trouble code is recorded.
(b)  To check that the malfunction is corrected when the repair is completed confirming that diag. trouble code

is no longer detected.

Malfunction: Open in EGR gas temp. sensor circuit

Disconnect the EFI fuse (15 A) for 10 sec. or more, with IG switch OFF.
Initiate test mode (Connect terminal TE2 and E1 of check connector or TDCL with IG
switch OFF).

Start the engine and warm up.

After the engine is warmed up, let it idle for 3 min.

With the A/C ON and transmission in 5th gear (ECT in 3rd speed) drive at 55 ~ 60 mph
(88 ~ 96 km/h) for 4 min or less.

HINT: If a malfunction exists, the ”CHECK” engine warning light will light up during step .

NOTICE: If the conditions in this test are not strictly followed, detection of the malfunction

will not be possible.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–105

DIAGNOSTIC CHART

Check voltage of VSV for EGR Power
source.

Check resistance of VSV for EGR.

Repair or replace harness or
connector.

Replace VSV for EGR.

Check for open and short in harness and
connector between EFI main relay and ECU.

Check and replace EGR.

Check EGR system (See page 

EC–12

).

Check resistance of EGR gas temp. sensor.

Check and replace EGR.

Check for open in harness and connector
between EGR gas temp, sensor and ECU.

Repair EGR system.

Replace EGR gas temp. sensor.

Repair or replace harness or
connector.

TR–106

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ENGINE TROUBLESHOOTING

Circuit Inspection