Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 126

13
OTHER CONTROL SYSTEMS
- ECT OD Cut-off Control System, Oxygen Sensor Heater Control System,
Lean Mixture Sensor Heater Control Syste m
ECT OD CUT-OFF CONTROL SYSTEM
The Engine ECU sends an OD (overdrive) cut-off
signal to the ECT ECU based on signals from the
water temperature sensor and vehicle speed
sensor to prohibit the transmission from shifting
into overdrive . The purpose of this control is to
maintain good drivability and acceleration
performance .
In some engines, the Engine ECU also sends a
3rd-gear cut-off signal to the ECT ECU .
For fu
rt
her details, see Step 3, vol .
4 (ECT) .
ECT ECU
Engine ECU
OXYGEN SENSOR HEATER
CONTROL SYSTE M
The Engine ECU controls the operation of the
oxygen sensor heater according to the intake air
volume and engine speed : When the engine load
is small and the exhaust gas temperature is
consequently low, this heater is operated to
maintain sensor efficiency . However, when the
engine load and exhaust gas temperature
increases greatly, heater operation is stopped to
prevent deterioration of the sensor .
Engine EC U
Oxygen
senso r
Heater
H T
E01 and E02
J
OHP 7 9
The OD cut-off signal and 3rd-gear cut-off signal
appear as follows :
(V)
Hig h
voltag e
Low
voltage
(less
than 1V )
(V)
Hig h
voltag e
Low
voltage
(less
than 1V)
(Normal
operating
condition )
OD cut-off
signa l
L
3rd-gear
cut-off
signal
OHP 79
LEAN MIXTURE SENSOR
HEATER CONTROL SYSTE M
The ECU controls the operation of the lean
mixture sensor heater according to the throttle
position, intake manifold pressure, engine speed,
and coolant temperature signals .
The temperature range in which the lean
mixture sensor can operate correctly is very
narrow, so the ECU keeps it within that range by
controlling the amount of current that it allows
to flow to the lean mixture sensor heater .
114 OHP 79