Lexus SC300 / Lexus SC400. Manual — part 671

Diag. Code 24

Intake Air Temp. Sensor Circuit

CIRCUIT DESCRIPTION

The intake air temp. sensor is built into the air flow meter and senses the intake air temperature.
The structure of the sensor and connection to the ECU is the same as in the water temp. sensor shown on page

TR–68

.

If the ECU records the diagnostic code ”24”, it operates the fail safe function, keeping the intake air temperature
at a constant 20

°

C (68

°

F).

Code No.

Diagnostic Code Detecting Condition

Trouble Area

24

Open or short in intake air temp. sensor circuit
for 0.5 sec. or more.

Open or short in intake air temp. sensor circuit.

Intake air temp. sensor

ECU

DIAGNOSTIC CHART

DIAGNOSTIC CHART

HINT: If diagnostic codes ”22” (water temperature sensor circuit), ”24” (intake air temperature sensor

circuit) and ”41” (throttle position sensor circuit) are output simultaneously, E2 (sensor ground) may
be open.

WIRING DIAGRAM

Check and replace ECU.

Replace water temp. sensor.

Check for momentary interruption

(See page

TR–23

).

Repair or replace harness or
connector.

Check voltage of sensor.

Check resistance of sensor.

Check for open and short in harness and
connector between ECU and water temp. sensor.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–72

NG

OK

OK

NG

OK

NG

INSPECTION PROCEDURE

1

Check voltage between terminals THA and E2 of engine & ECT ECU connector.

C

OK

P

(2) Connect the Check Harness A.

(See page TR–30)

(2) Turn ignition switch on.

Measure voltage between terminals THA and
E2 and engine & ECT ECU connector.

Check for momentary Intertuption
(See page

TR–23

).

2

Check intake air temp. sensor.

C

OK

P

Disconnect the air flow meter connector.

Measure resistance between terminals 1 and 2 of air
flow meter connector.

Resistance is within Acceptable Zone on chart.

Replace intake air temp. sensor (Replace air flow meter).

3

Check for open and short in harness and connector between engine & ECT ECU and intake air

temp. sensor (See page

IN–27

).

Repair or replace harness or connector.

Check and replace engine & ECT ECU.

TR–73

–

ENGINE TROUBLESHOOTING

Circuit Inspection

Diag Code

25

Air–Fuel Ratio Lean Malfunction

Diag. Code

26

Air–Fuel Ratio Rich Malfunction

CIRCUIT DESCRIPTION

Refer to page

TR–62

for the circuit description.

Code No.

Diagnostic Code Detecting Condition

Trouble Area

(1)

Main oxygen sensor voltage is 0.45 V or less (lean)
for 90 sec. under conditions (a) and (b).
(2 trip detection logic)*
(a) Coolant temp.: 60

°

C (140

°

F) or more.

(b) Engine speed: 1,500 rpm or more.

Open or short in main oxygen sensor circuit

Main oxygen sensor

Ignition system

Water temp. sensor

25

⋅

26

(2) Main oxygen sensor voltage is alternating

above and below 0.45 V at 5 times par
second or more under conditions (a) and (b).
(2 trip detection logic)*
(a) Engine speed: Idling
(b) Coolant temp.: Between 60

°

C (140

°

F)

and 95

°

C (203

°

F)

Open or short in injector circuit.

Fuel line pressure (injector blockage)

Air flow meter (air intake)

Engine ground bolt loose

Foreign object caught in valve

(3) Difference of air–fuel ratio feedback compensation

value between right and left banks is more than 10
percentage for 30 sec. or more under conditions (a)
and (b).
(2 trip detection logic)*
(a) Engine speed : 2,000 rpm or more.
(b) Coolant temp.: Between 60

°

C (140

°

F)

and 95

°

C (203

°

F)

Fuel line pressure (injector leak, blockage)

Mechanical system malfunction

(skipping teeth of timing belt)

Ignition system

*: See page

TR–21

.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–74

CIRCUIT DESCRIPTION (Cont’d)

DIAGNOSIS CODE DETECTION DRIVING PATTERN

Purpose of the driving pattern.

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

is no longer detected.

Malfunction: Open or Short in Main Oxygen Sensor

Initiate test mode (See page

TR–12

).

Start engine and warm up.

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

Perform quick racing to 4,000 rpm three times by accelerator pedal.

After performing the racing in (4), perform racing at 2,000 rpm for 90 sec.

HINT: If a malfunction exists, the ”CHECK” engine warning light will light up after 90 sec. from the

start of racing.

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

will not be possible.

TR–75

–

ENGINE TROUBLESHOOTING

Circuit Inspection