Hi, firstly, why do you want to reset your ecu? If you have had a fault error, then a session on a Lexia would be the way forward. some apps on mobiles with a blue tooth dongle can reset some codes. However, on my 2.0 HDi estate, can be reset by turning the ignition key to on (before actual start) and off 12 times sometimes works. Also I have followed the instruction on the Frenchcar forum, as follows;
ignition off - lights on - remove battery terminals - the wired tails (no battery) short together, this discharges the ecu - light off - reconnect the battery - reset the time clock - radio stations - electric windows. If you are near the North West,I have Lexia kit.
Hope this helps.
Mick H
April 2014