TOYOTA PREVIA 91-97 REPAIR MANUAL

DRIVEABILITY AND EMISSIONS CONTROLS 4-17

EGR Vacuum Modulator

» See Figure 47

1. Unbolt the vacuum modulator bracket and extract.


2. Label and disconnect the hoses attached to the modulator.


3. Pull the clips apart and remove the modulator.
   To install:


4. Insert the modulator into the bracket clips.


5. Attach the hoses in their proper positions.


6. Position the bracket/modulator assembly on the engine and secure
   the mounting bolts to 9 ft. Ibs. (12 Nm).

Fig. 47 The throttle body ports are marked for the proper hoses

ELECTRONIC ENGINE CONTROLS

General Information

The Electronic Fuel Injection (EFI) system precisely controls fuel injection to

match engine requirements. This in turn reduces emissions and increases dri-

veability. The ECM receives input from various sensors to determine engine

operating conditions. These sensors provide the input to the control unit which

determines the amount of fuel to be injected as well as other variables such as

idle speed. These inputs and their corresponding sensors include:

• Intake air temperature—Intake Air Temperature Sensor


• Coolant temperature—Water Temperature Sensor


• Engine speed—Puise signal from the distributor


• Throttle valve opening—Throttle Position Sensor


• Exhaust oxygen content—Oxygen Sensor

Engine Control Module (ECM)

OPERATION

The ECM receives signals from various sensors on the engine. It will then

process this information and calculate the correct air/fuel mixture under all

operating conditions. The ECM is a very fragile and expensive component.

Always follow the precautions when servicing the electronic control system.

PRECAUTIONS

**CAUTION

Some models covered by this manual may be equipped with a
Supplemental Restraint System (SRS), which uses an air bag.
Whenever working near any of the SRS components, such as
the impact sensors, the air bag module, steering column and
instrument panel, disable the SRS, as described in Section 6.

• Do not permit parts to receive a severe impact during removal or
  installation. Always handle all fuel injection parts with care, especially the
  ECM. DO NOT open the ECM cover!


• Before removing the fuel injected wiring connectors, terminals, etc.,
  first disconnect the power by either disconnecting the negative battery cable
  or turning the ignition switch OFF.


• Always check the diagnostic trouble code before disconnecting the
  terminal cable from the battery.


• Do not be careless during troubleshooting as there are numerous
  amounts of transistor circuits; even a slight terminal contact can induce
  troubles.


• When inspecting during rainy days, take extra caution not to allow entry
  of water in or on the unit. When washing the engine compartment, prevent
  water from getting on the fuel injection parts and wiring connectors.

REMOVAL & INSTALLATION

> See Figure 48

The ECM is located on the drivers side of the vehicle bolted to the front

seat leg. Refer to the Precautions prior to removal of the ECM. Checking for

trouble codes before removal is recommended.

1. Check for any trouble codes. Refer to the procedure later in this sec-
   tion.


2. Note any electronic device settings such as the radio stations, clock
   etc. These will no longer be set once the battery cable is disconnected.


3. Disconnect the negative battery cable. Wait at least 90 seconds
   before proceeding on models equipped with an air bag.

ECU Connector

LH Front Seat Leg

Fig. 48 The ECM is secured behind the driver side seat leg