You may want to reset your ECU because you want to clear a fault code or simply to let you ECU re-learn your settings again, say after a modification or change in fuel (octane).
In summary classic Impreza's can be manually reset and new age Impreza's onwards have to reset using a tool plugged in to the diagnostics port.
New Age (Denso) ECU Reset
The Denso ECU's don't have a manual reset function like the JECS ones. The Denso units apparently have a non-volatile RAM, so even disconnecting the battery won't do it. The only way to reset these ECUs is via the OBDII diagnostics port using a computer. Until recently this has only possible at the main dealer or using other commercial solutions e.g. Delta Dash or SECS.
What follows is a description of resetting your Newage ECU using ecuExplorer which, at the time of writing, is distributed free by TARI Racing. This software is described in more detail in the ECU diagnostics and data logging technical article.
- Download and install the latest release of ecuExplorer
- Connect up to the OBDII diagnostics port with reference to the connecting to your ECU technical article.
- Turn on your ignition
- Invoke ecuExplorer and select the Tools -> Reset ECU option as illustrated in the figure below.
- To complete the reset, turn your ignition off, back on, then start your car.
Figure 1 - ecuExplorer Reset ECU option
Classic (JECS) ECU Reset
- Ensure engine is at normal operating temperature, turn engine off
- Locate the two ECU connectors, located under the steering column and consist of a black plastic male and female connector, and a green male female connector
- With the ignition OFF connect black to black and green to green.
- Turn on ignition, do not start the engine, depress the accelerator pedal to full throttle, then return it to the half-throttle position and hold for a few seconds, and then release
- Engine Check lamp turns on
- Start engine and then drive for at least one minute, keeping road speed above 11 Km/h.
- ECU is now re-set.
- At this point the check engine light should start to flash the all clear signal (steady 1/2 second interval flashes). If the check engine light does not flash, or indicates some other sequence, there is a fault present in the system, and should be professionally checked for necessary repairs.
- Stop the car and turn off the engine.
- Disconnect the black and green connectors.
- Job complete
Black and Green Connectors on Classic
Information source - ScoobyNet, author - wah