Input Signals - Toyota Camry 1999 Electrical Troubleshooting Manual

SYSTEM OUTLINE
This system utilizes an engine control module and maintains overall control of the engine, transmission and so on. An outline
of the engine control is explained here.

1. INPUT SIGNALS

(1) Engine coolant temp. signal circuit
The engine coolant temp. sensor detects the engine coolant temp. and has a built–in thermistor with a resistance which
varies according to the water temp. is input into TERMINAL THW of the engine control module as a control signal.
(2) Intake air temp. signal circuit
The intake air temp. sensor is installed in the mass air flow meter and detects the intake air temp., which is input as a
control signal into TERMINAL THA of the engine control module.
(3) Oxygen sensor signal circuit
The oxygen density in the exhaust gases is detected and input as a control signal into TERMINALS OXL1, OXR1
(Except California) and OXS of the engine control module. To maintain stable detection performance by the heated
oxygen sensor, a heater is used for warming the sensor. The heater is also controlled by the engine control module
(HTL, HTR (Except California) and HTS).
(4) RPM signal circuit
Camshaft position and crankshaft position are detected by the camshaft position sensor and crankshaft position sensor.
The camshaft position is input as a control signal to TERMINAL G22+ of the engine control module, and the engine
RPM is input into TERMINAL NE+.
(5) Throttle signal circuit
The throttle position sensor detects the throttle valve opening angle as a control signal, which is input into TERMINAL
VTA1 of the engine control module.
(6) Vehicle speed signal circuit
The vehicle speed sensor, installed inside the transmission, detects the vehicle speed and inputs a control signal into
TERMINAL SPD of the engine control module.
(7) Park/Neutral position SW signal circuit
The Park/Neutral position SW detects whether the shift position is in neutral, parking or not, and inputs a control signal
into TERMINAL STA of the engine control module.
(8) A/C SW signal circuit
The A/C control assembly (Automatic A/C) or A/C Amplifier (Manual A/C) inputs the A/C operations into TERMINAL A/C
of the engine control module as a control signal.
(9) Battery signal circuit
(California or w/ engine immobiliser and/or traction control)
Voltage is always supplies to TERMINAL BATT of the engine control module.
If you turn on the ignition SW, the current goes from TERMINAL MREL of the engine control module to the EFI relay and
put on the relay, and the voltage related to the engine control module operation is supplied to TERMINAL +B of the
engine control module through the EFI relay.
(Except California or w/ engine immobiliser and/or traction control)
Voltage is constantly applied to TERMINAL BATT of the engine control module. When the ignition SW is turned on,
voltage for engine control module start–up power supply is applied to TERMINAL +B of engine control module via EFI
relay.
(10) Intake air volume signal circuit
Intake air volume is detected by the mass air flow meter and a signal is input into TERMINAL VG of the engine control
module as a control signal.
(11) NSW signal circuit
To confirm whether the engine is cranking, the voltage applied to the starter motor during cranking is detected and the
signal is input into TERMINAL NSW of the engine control module as a control signal.
(12) Engine knock signal circuit
Engine knocking is detected by the knock sensor 1 and 2, then the signals are input into TERMINALS KNKR and KNKL
of the engine control module as a control signal.
(13) Air fuel ratio signal circuit (California)
The air fuel ratio is detected and input as a control signal into TERMINALS AFL+, AFR+ of the engine control module.