Electronic control unit or ECU is the brain of modern automobiles. It is responsible for delivering proper air/fuel mixture, advancing/retarding timing and other parameters that are necessary to keep an engine running. ECU is generally connected to the car via one or more wiring harnesses. From under the hood, you may follow the bunch of wires going into the car through the firewall. ECU may end up in any of these common areas.
1. Under Center Console
The highest easily accessible part of a car where the ECU can be mounted is under the center console, in front of the shifter.
2. Kick panel
Below the glove compartment or steering column is the kick panel. Early models of Suzuki Samurai have their ECUs hidden beneath the kick panel trims.
3. Steering Column
Some vehicles for off-roading have their ECUs installed in the highest hidden point in the car, like the Tracer and Sidekick. ECU may be located near the steering column, and is covered in plastic to prevent water from flooding the unit.
4. Under the floor
Some ECUs are located on the passenger side, or the foot rest area. ECUs under the floor are much harder to find because it might be necessary to loosen the door jam to pull back the carpet.