Toyota Previa 1991-1997 Repair Information

Engine Control Module (ECM)



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.


Some models covered by this guide 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 Chassis Electrical .

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, ect., 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.


See Figure 1

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 section.
  3. Note any electronic device settings such as the radio stations, clock ect. These will no longer be set once the battery cable is disconnected.
  5. Disconnect the negative battery cable. Wait at least 90 seconds before proceeding on models equipped with an air bag.
  7. From under the drivers seat, unbolt the ECM form the leg.

Click image to see an enlarged view

Fig. Fig. 1: The ECM is secured behind the driver side seat leg

  1. Carefully disengage the 3 harnesses form the ECM.

To install:
  1. Attach the harnesses to the ECM. Secure to the seat leg with the mounting bolts.
  3. Connect the negative battery cable. Reset any electronic devises such as the radio, clock, ect.