Car owners might accidentally affix the jumper cables in turning back order or download the battery backward, which causes the vehicle to no much longer start.

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The objective of this troubleshooting guide is to assist answer the adhering to questions:

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Connecting the jumper cables backward or installation a new battery the wrong method is never fun. In this article, girlfriend will uncover troubleshooting actions that will aid you diagnose together problems. 

Installed brand-new battery backward, the vehicle won"t start.


You chose to change the car battery however accidentally put the cables backward. Rather of connecting the positive (+) cable to the optimistic battery terminal and also the negative (-) cable to the an unfavorable battery terminal, girlfriend hooked them up backward.

 All of a sudden, you see a scary spark, and your vehicle goes completely dead. The car will no much longer start. Dashboard lights room off, and also everything is dead. The an essential may not also turn the ignition. Similar symptoms will be experienced when you try to jump-start a dead battery yet accidentally affix the jumper cables backward. 

When a vehicle battery is linked backward, a fuse designed come protect vehicle electronics have to blow. If your car doesn"t have actually a fuse (almost all cars do) designed for this purpose, you will certainly send electrical present backward through systems in her car, including ECU, transmission control unit, and also more.

If present flows backward v lights, that"s not a trouble when present flows backward through electronics with diodes such as the ECU / ECM (Engine regulate Unit / Module).

It is not typical to damage the Engine control Unit / Module by disconnecting the battery cables.

Most the them room designed to resist reverse polarity. In the worst case, the ECU/ECM have the right to be removed and inspected if a diode has actually failed. 

Troubleshooting auto Won"t start Problem

Step 1


Check the high ampere fuses in your car. Many vehicles have a huge fuse that will certainly blow and avoid damages to the ECU / ECM. This might be a 40, 60, 80-ampere fuse, and also it is usually tough to find.

Here is a photo of this fuse ~ above a Honda Civic. When the jumper cables were linked backward, this fuse blew. This is from a 2015 Honda Civic. 

Notice the fuse strip. More than one fuse deserve to blow. Once you change this fuse, begin up the car.

In many cases, the automobile should start appropriate up. If the doesn"t, proceed to step 2. 

Step 2


After you change the swollen fuse, you might still have actually a problem starting the engine. The engine might turn over and crank, however it will certainly not start.

Now it is time to check all the smaller fuses. Ensure that the fuse for the ignition system, ECU, fuel pump, Immobilizer is tho good. 

Step 3

If every the fuses are still great and your automobile still refuses to start, right here are a couple of things you need to check. 

The auto turns over but won"t start. 

Check if there is a spark in ~ the plugs.Check fuel pressureCheck if direct injectors are acquiring power.

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The vehicle won"t revolve over or crank. 

Immobilizer systemEngine control Unit is obtaining powerCheck to view if the starter is obtaining power.

Step 4


Hopefully, you were able to diagnose the difficulty yourself. If you room still having difficulties with beginning the car, you may want to take into consideration having a mechanic look at her car. Protect against letting water or rainfall on her fuse panel.