Lexus SC300 / Lexus SC400. Service manual - part 676

Diag. Code    35

High Altitude Compensator Sensor
(HAC Sensor) Circuit

CIRCUIT DESCRIPTION

The HAC sensor is built into the ECU. This is a semiconductor pressure sensor with properties which cause its
electrical resistance to change when stress is applied to the sensor’s crystal (silicon) (piezoelectric effect). This
sensor is used to detect the atmospheric (absolute) pressure and outputs corresponding electrical signals. Fluc-
tuations in the air pressure cause changes in the intake air density, which can cause deviations in the air–fuel
ratio. The signals from HAC sensor are used to make corrections for these fluctuations. If the ECU records diag-
nostic code ”35”, the fail safe function operates and the atmospheric pressure is set at a constant 760 mmHg.

Code No.

Diagnostic Code Detecting Condition

Trouble Area

35

Open or short detected in HAC sensor circuit for 0.5

sec. or more.

ECU

DIAGNOSTIC CHART

DIAGNOSTIC CHART

Are there any other codes (besides Code 16)
being output?

Replace engine & ECT ECU.

Go to relevant diag. code chart.

TR–92

–

ENGINE TROUBLESHOOTING

Circuit Inspection

–MEMO–

ENGINE TROUBLESHOOTING

TR–93

Diag. Code   41, 47

(Sub–) Throttle Position Sensor Circuit

CIRCUIT DESCRIPTION

The throttle position sensor is mounted in the throttle body
and detects the throttle valve opening angle. When the
throttle valve is fully closed, the IDL contacts in the throttle
position sensor are on, so the voltage at the terminal IDL of
the ECU become 0 V. At this time, a voltage of approximately
0.7 V is applied to the terminal VTA of the ECU. When the
throttle valve is opened, the IDL contacts go off and thus the
power source voltage of approximately 12 V in the ECU is ap-
plied to the terminal IDL of the ECU. The voltage applied to
the terminal VTA of the ECU increases in proportion to the
opening angle of the throttle valve and becomes approxi-
mately 3.5–5.0 V when the throttle valve is fully opened. The
ECU judges the vehicle driving conditions from these signals
input from the terminals VTA and IDL, and uses them as one
of the conditions for deciding the air–fuel ratio correction,
power increase correction and fuel–cut control etc. The sub–
throttle position sensor is built and operates in the same way
as the main throttle position sensor. This sensor is used for
traction control. The sub–throttle valve is opened and closed
by the sub–throttle actuator according to signals from the
TRAC ECU to control the engine output.

Code No.

Diagnostic Code Detecting Condition

Trouble Area

41

(1) Open or short in throttle position sensor circuit

(VTA1) for 0.5 sec. or more.

Open or short in throttle position sensor cir-

cuit.

41

(2) IDL1 contact is ON and VTA1 output exceeds 1.5

V for 0.5 sec. or more.

Throttle position sensor

ECU

47

(1) Open or short in sub–throttle position sensor 

circuit (VTA2) for 0.5 sec. or more.

Open or short in sub–throttle position sensor

circuit.

47

(2) IDL2 contact is ON and VTA2 output exceeds 

1.5 V for 0.5 sec. or more.

Sub–throttle position sensor

ECU

HINT:

Diag. code 41 is for the throttle position sensor circuit.
Diag. code 47 is for the sub–throttle position sensor circuit.

•

When the connector for the (sub–) throttle position sensor is disconnected, diagnostic code 41 or 47 is not
displayed. Diagnostic code 41 or 47 is displayed only when there is an open or short in the VTA signal circuit
of the (sub–) throttle position sensor.

•

Signals from the (sub–) throttle position sensor are also input to the TRAC ECU, So when a malfunction
occurs on the TRAC side, code 41 or 47 may be displayed.

TR–94

–

ENGINE TROUBLESHOOTING

Circuit Inspection

DIAGNOSTIC CHART

DIAGNOSTIC CHART

HINT:

•

If diag. code 41 is displayed, check throttle position sensor circuit; if diag. code 47 is displayed,
check sub–throttle position sensor circuit.

•

If diag. 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.

Adjust or replace throttle position
sensor.

Check for momentary interruption
 (See page 

TR–23

).

Repair or replace harness or
connector.

Check voltage of throttle position sensor.

Check operation for throttle position sensor.

Check for open and short in harness and
connector between throttle position sensor and ECU.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–95