Check Engine Light On After Battery Change: Fixed!

Changing your car’s battery is an easy task. Unfortunately, it can sometimes lead to an immediate check engine light on. It might leave you with concern that what wrong you have done to your engine. So, let’s discuss how to deal with the problem.

If you have just changed the battery and checked engine light has come on, you should first check if the new battery has a low charge or is faulty, battery terminals are loose or the battery cables have become bad. If you have inspected these things and check engine light is still on, it might not be because of a new battery. You will need to use OBD2 scan tool to read related trouble codes stored in your engine’s computer memory to find the root cause of a check engine light.

Read my guide on car won’t start after replacing battery if your car stalls or won’t start after battery change.

Why Is Check Engine Light On After Battery Change?

After the battery change, the check engine light can be on due to low voltage trouble codes that are caused by a weak or dead battery.

Sometimes, the check engine light is on and the engine’s computer starts giving trouble codes related to the electric circuit of different engine sensors after disconnecting and reconnecting the battery.

Some random low voltage codes or loss of communication codes (U0100, U0140) can pop up when your disconnect the battery, or the car battery becomes dead and does not supply sufficient voltage to the engine computer and electric circuits of different engine sensors. For instance, one user found the trouble code P0882 when his car’s battery was dead. The code was related to a lower input power signal to the ECM.

So, in those cases, the chances are that the check engine light resets or goes off automatically after you clear the codes using the OBD2 scan tool and drive your car for a couple of days or complete 10 to 20 drive cycles or complete around 50 to 100 miles of the drive. Make sure that the engine temperature is close to the ambient air temperature at the start of each drive cycle. If the check engine light after the battery change is still on after several drive cycles, there’s obviously still an active issue going on.

Before trying to fix the check engine light, you can also first try clearing the code by turning the key into the on position for a minimum of 10 seconds before starting the engine. This allows relearning the system after reinstalling the battery. You could repeat this twice but make sure to end with the key in the ‘ON’ position. You can also first drain the battery by disconnecting the negative cable first for 15 minutes, pressing the horn, and turning on the headlights to drain any electric charge stored in the engine. After that, connect the negative cable of the battery and do 10 seconds trick of clearing the codes.

Causes Of Check Engine Light On After Battery Change

Check engine light on after battery change is due to the following reasons:

1. Battery Is Weak Or Dead

Check engine light on after battery change is something that could happen if the battery is dead, weak, or the alternator has failed. There are many different things that can go wrong with your battery. The battery may not be charging properly and could possibly leak. This could cause the check engine light to come on.

To check whether the battery is weak, you have to perform a voltage test across the battery posts. Have someone turn the key and start the engine, while you put the voltmeter probes on the battery posts. If the battery voltage drops below 9V when trying to start, the battery is run down or defective.

You should note the following things when replacing a new battery to avoid its damage:

• Make sure your car battery belongs to the correct group (the size of the battery). Otherwise, cables may not reach the battery posts. You should also consider the reserve capacity (how long the battery can run the car if your alternator fails) and Cold-cranking amps rating (how well the battery performs in cold weather) of your battery. These factors are usually specified in the owner’s manual.
• There is sufficient clearance between the bonnet and the replacement battery to avoid terminals shorting/fouling on the closed bonnet.
• If you do not replace and tighten the hold-down clamp securely so that the battery cannot move in the tray. Moreover, overtightening a hold-down can also damage the plastic battery casing and result in battery acid leaking.
• Clean the battery tray of all debris to ensure no sharp objects can damage the plastic battery casing.
• Make sure that new battery terminal posts are positioned exactly the same as the battery being replaced.

2. Loose or Corroded Battery Terminals

If you’ve ever had your check engine light come on after a battery change, it’s likely because your battery terminals were loose. While it may seem like a small thing, loose battery terminals can actually cause a number of problems. For one, they can cause your check engine light to come on.

Loose battery terminals can also cause your battery to drain more quickly than it should. This is because the loose connection can cause your alternator to work harder than it needs to.

There are a few things that can cause the battery terminals to become loose. The most common is simply that the terminals were not tightened properly when the battery was installed. Another common cause is that the battery terminals are corroded. This can happen if the battery is not properly maintained. If the battery acid leaks out, it can corrode the terminals. So, whenever a battery is replaced, ensure the terminals and battery posts are cleaned before installation.

You can use a small wire brush to clean the dust and scrap the corrosion particles. After that, clean the battery terminals with a mixture of water and baking soda. You can also apply a thin layer of petroleum jelly to the battery terminals. 

Also, make sure the battery terminal is fully seated against the post of the battery. I had this problem when I didn’t push the terminal down far enough over the post. You can use a rubber mallet to lightly tap the battery terminal. If you hammer hard, it could damage the battery posts and cause internal leakage to the battery.

3. Short To Ground

If you mistakenly remove the negative terminal first or install the positive terminal of the battery first, a short circuit might occur at some point in the car if the wrench touches the car’s body in the process of tightening up or loosening the battery terminals. As a result of a short to ground, the ECM will turn on the check engine light due to a loss of communication between the sensors and the ECM.

Moreover, if the wrench mistakenly touches the vehicle’s chassis while removing the positive terminal first, it will pull a lot of currents and the spark will be hot enough to destroy the battery with a dead short.

4. Battery Cables Are Damaged

Battery cables are the thick wires that connect your car battery to the rest of your car’s electrical system. They are responsible for delivering power from the battery to the starter, alternator, and other electrical components. 

Over time, battery cables can become damaged, due to corrosion, loose connections, or physical damage. When this happens, they can no longer effectively deliver power to your car’s electrical system, which can lead to all sorts of problems. 

Also, while replacing the car battery, the wires may chafe, shed their insulation, and contact the vehicle’s body or engine, causing a short circuit. It will also turn on the check engine light.

Can A New Battery Cause A Check Engine Light?

A new battery can cause a check engine light if the new battery has a low charge or the terminals are not tightened properly on the battery posts. If the battery has a low charge, the ECM will throw low voltage or loss of communication trouble codes that will trigger the check engine light.

Moreover, if the plastic casing of the battery becomes damaged while tightening the hold-down clamps, the acid will leak, and the battery will be dead.

So, if you do install your own battery, make sure that you follow the instructions that came with the battery. If you don’t follow the instructions, you may damage your car.