I have a Renault Clio car. I replaced my car battery with a new one. I tried to start the car but it's not worked. After it makes a smoke from the engine side. Finally I see I had connected the battery wrongly. I had connected it negative terminal to positive terminal. After that I quickly disconnect the battery and connect rightly. When I start again the car now the indicators of the dashboard, AC, radio and all are working but the starter motor running slowly. Also the car engine isn't starting. I think ECU in the car is almost working. Can you please tell me what is the problem?
You may have damaged many things...
For the ecu, "almost working" means nothing, if that does not work 100% then the car may not start (as you have now) or may not run correctly.
You may need to have the ecu tested, if it is ok then possibly re-programmed. Or you will need a new ecu and have that coded or programmed to match the car.
There are other control units that may also be affected as well.
Before you start replacing the ECU etc, check the simple (and cheap) things first!
If you had smoke coming from something, you were taking a very high current from the battery when it was connected the wrong way round.
If the starter is only cranking slowly, you may have discharged the battery, or damaged it internally, so it can't deliver enough power to start the car, even though it will power the radio, lights, etc.
Try recharging it. If that doesn't work get the battery tested by a garage and replace it if it necessary.
Also check for any blown fuses.
If that still doesn't work, then you have probably damaged something else in the electrical system, which will be more expensive to fix!