Car Does nothing after hooking jumper cables backwards

Tiny
GREGORY L. JACKSON
  • MEMBER
  • 2006 MERCEDES BENZ 350SL
  • 1.6L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 100,000 MILES
My E350 battery was weak, So I jumper cabled the battery. But, I accidently put the positive cable on the negative terminal and the negative cable on the positive terminal. Now the car will do nothing: wont recognize the smart key, no horn, lights, etc. I just jumpered it the correct way a few minutes ago, Some lights came on, but overall, no change: Car does not recognize smart key, key wont tern, no horn, etc. Help Please. Thank you. Greg
Wednesday, April 3rd, 2019 AT 11:54 AM

4 Replies

Tiny
JOETECHPRO
  • MECHANIC
  • 705 POSTS
Hey Gregory L. Jackson,

First thing to do will be to check all of the fuses. Guide below.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

By connecting the two batteries in series you have effectively doubled the battery voltage.

This will cause all consumers to try and draw twice the current that they normally would.

You need to check all of the regular and mini fuses along with the large power supply fuses.

Work your way through all of these first.

If your battery is dead, replace it.

Try again and see what you get.

You may have done some damage to the control units in the vehicle but the first step is to get rid of that battery and replace any fuses that are blown.

Regards, Joe
Was this
answer
helpful?
Yes
No
+1
Wednesday, April 3rd, 2019 AT 6:13 PM
Tiny
GREGORY L. JACKSON
  • MEMBER
  • 1 POST
Thank you Joe, I'll try, but everything I look up says I probably destroyed some relay's and/or control module when I hooked the jumper cables on backwards. Please help. Used module? It is a 2007 Mercedes Benz E350. I don't want to spend more on repairs then the car is worth. Thank you for your reply. Sincerely, Gregory
Was this
answer
helpful?
Yes
No
Friday, April 5th, 2019 AT 9:37 AM
Tiny
GREGORY L. JACKSON
  • MEMBER
  • 1 POST
Joe, one more thing I forgot to add on the 2007 Mercedes Benz E350: Ever since I hooked up the jumper cables wrong (reverse positive cable on negative post), the car won't do anything: The key won't turn in the ignition, the car won't recognize the key, the windows are down and won't roll up, the sunroof is open and won't close, no horn, no nothing. I know I fried the battery, so I had someone jump me correctly: The trunk lights came on, but that was all. Nothing, including the key doesn't work, nothing works. Everything I read says I most likely ruined come type of control module. I don't want to spend more on the car then it is worth. Help please! Used module? Any suggestions? Thank you for your reply. Gregory
Was this
answer
helpful?
Yes
No
Friday, April 5th, 2019 AT 9:38 AM
Tiny
JOETECHPRO
  • MECHANIC
  • 705 POSTS
Hey Gregory L. Jackson,

As I said before, before jumping to control unit replacement you need to replace that battery and check and replace any blown fuses.

Let me know what you have after doing this.

Regards, Joe
Was this
answer
helpful?
Yes
No
Friday, April 5th, 2019 AT 10:39 AM

Please login or register to post a reply.

Related Battery Jump Content

How to Jump Start a Battery
VIDEO
How to Jump Start a Battery
Instructional repair video
Battery Jump Start
GUIDE
Battery Jump Start
A battery jump start is easy to do but can be hazardous if not performed correctly. This guide will show you the do's and don'ts to keep you safe, and get you back on the...