How to Repair a Backwards Battery Connection - Reversed Polarity

It is easy to connect a battery backwards and it happens more than you think, so don't feel bad if you are here for that reason. Your car has safeguards built in to help protect against situations like this which we will go over in this guide and how to fix them, so sit right down and we can fix this problem together. First of all be safe when working with a battery because it contains battery acid which you should safe gauge yourself against by wearing gloves and protective eyewear. Wash your hands and don't touch clothing, skin or your eyes.

First Steps

Immediately disconnect the battery and reconnect it correctly. Depending on the model and year of the car, electrical items may not work due to the reversed polarity, please follow this guide.

Fixing the Problem

1. Locate the main fuse panel which will be close to the battery, either under the hood or in the trunk of the vehicle. Inside the fuse panel will have a fusible links, or a maxi fuses which are the main protection devices designed to protect the electrical system and modules. Both maxi fuses and fusible links can be checked by visual inspection or by using a test light. These electrical safeguards are used to handle the main electrical current of the vehicle and designed to fail when a main electrical event has occurred.

2. Once you have gone over the main power fuses turn the ignition switch or start button. This will power up the remainder of the sub-fuses in the main and sub fuse panels, there can be as many as five depending on the configuration of the car. It you don't know the location of the fuse panels please consult the owners manual or ask one of our experts to help for free. Checking these fuses is the same procedure as the maxi-fuses which can be done either visually or by test light.

3. Now that all fuses and maxi fuses are tested, try to start the car. If it wont crank over or the engine cranks over but not start it is time to scan the CAN system for trouble codes to see what codes are stored. This can point to any modules such as the security system computer, BCM or PCM that may have shorted out during the event. These modules have a built-in safety system which can tell if they are having problems internally in most cases. If the security light is flashing while the engine is cranking over the security system is having an issue and needs to be reset.

4. If the engine starts, take the car for a test drive to see if all accessories are operating correctly or if there are any warning lights on. Depending on the system that needs attention, each problem will need to be addressed individually.

Prevention

Avoiding the problem in the first place:

• Use you phone to take a picture of the battery before removal, note the position of the battery terminals.
• Observe that the positive battery terminal is slightly larger than the negative terminal.
• Don't trust that all positive battery cable colors are red or that the negative cables are black.
• All batteries are have a small (+) or (-) sign near the battery terminals

Watch the Video!

Please watch this video of the job being done to glean additional helpful information.

Credits

This guide knowledge base was created by the 2CarPros Team, and by Ken Lavacot: Automobile repair shop owner and certified master automobile technician of over 30 years. If you have question or need help please ask one of our experts we are happy to help. Please visit our 2CarPros YouTube Channel.