Hi all! been a LONG time since I have popped in here!

Anyway, Im looking for some help. I reversed the terminals when re-installing my cars battery  I know.... Yea, Anyway... Now I get only a few lights and it wont try to start. I checked all the fuses even the large 100 A under the hood.. They are all good. Even bought a new battery today.. Still no go.

Did I fry my ECU? How can I tell?

Its a 98 Hyundai Elantra

HELP! 

No clue how to fix this but I wish you the best of luck. I'm sure you'll get some good advice soon.

First off, I would expect there should be some diode blocking on the ECU to stop it dying from a backwards connection.. but who knows auto manufacturers who love selling parts..

I would recommend pulling all auxilary fuses, just keep the starter solenoid and ECU, airbags etc.

Is your battery going flat with nothing on? Usually a good indicator of smoke having escaped. Hopefully from a cheap part that doesn't stop the car from working..

There are some items that can pop with a reversed connection - fuel pump, alternator and other items that have a diode in them to prevent damage when they are expecting the battery to be connected properly - these may have popped, but I would expect to see a fuse go with them.

You have my sympathy - I have had a battery fail which almost took out all my electrics.. let us know how you get on.

what few lights? .... dash / warning lights? ... parking lights? ..

it doesnt sound that hopeful ... bit like making an incorrect connection for a jumpstart .. you can bugger the ECU up just by doing it wrong.... so if you have done a backwards battery (which is kinda more direct into the power circuit) its not going to be pretty i think...

best bet to check up would be like a thread on whirlpool forum maybe or a search for your "put battery cables in backwards on elantra" .. see who else has made that oopsie...

if it is the ECU i dont know that you can tell without a diagnostic tune machine/program directly hooked into the ecu ...

.. you checked the fuses .. but what about the fusible links? ... dont know if you have them but they look like little plastic barrels with wires out the ends and/or relays .. should be near the engine bay fuses ..

think right now the best bet 'might' be to get a mobile mechanic/diagnostic man out and get them to check... cost you a few bucks .. but you can at least tell them just to check ... if its a cheap fix then ok.. but if its a tricky/expensive fix/continuation then you can call a halt and investigate your online options further ...

i'm sending 'hope its cheap' thoughts in your direction!! 

You can rent an ECU diagnostic tool from places like AutoZone and Advance Auto. If you get a read error or a bunch of errors...well, you know the thing is cooked.

Quote from: Kijona on June 27, 2013, 10:12:44 PM
You can rent an ECU diagnostic tool from places like AutoZone and Advance Auto. If you get a read error or a bunch of errors...well, you know the thing is cooked.

thats cool!... dont know if we have that kinda thing in Aussie ... be good if they did though!!... you Yanks got everything!! 

you try disconnecting battery for a while then reconnecting  and see what happens?
BTW i stlil cant believe youre not buttercup lol

Quote from: Janx101 on June 27, 2013, 10:20:28 PM

Quote from: Kijona on June 27, 2013, 10:12:44 PM
You can rent an ECU diagnostic tool from places like AutoZone and Advance Auto. If you get a read error or a bunch of errors...well, you know the thing is cooked.

thats cool!... dont know if we have that kinda thing in Aussie ... be good if they did though!!... you Yanks got everything!! 

Hah. It comes at a price, believe me.

OP lives in the US of A in Pennsylvania, per his Profile.

Haha! Yama! =) Good to see a few of the old faces still around.

Im pretty sure its the ECU.. Still checking some things.. After it sat for a bit now everything comes on, even the radio. But, as soon as I turn the key past ignition to start.. Every thing cuts off and the dome light dims.. I pull the terminals and everything re-sets... 

fuseable links? those work like a fuse but are in the wiring. jump to an elantra forum and see what.you find.

Quote from: scottpA_GS on July 08, 2013, 03:17:30 PM
Haha! Yama! =) Good to see a few of the old faces still around.

Im pretty sure its the ECU.. Still checking some things.. After it sat for a bit now everything comes on, even the radio. But, as soon as I turn the key past ignition to start.. Every thing cuts off and the dome light dims.. I pull the terminals and everything re-sets... 

im assuming youve got a chipped key? ( security chip) reset the ecu and see if that helps. what youre descriping, sounds to me like the ecu sees the key as not oem, and is say6ing " no start for you"