Transmission Problems Caused by Battery Terminal Corrosion
Every so often you notice it: The transmission shifts a little late, or maybe it seems to miss a gear entirely. Then it’s okay again… for a little while. Worst of all, there’s no rhyme or reason behind the condition. One minute it’s fine, the next it’s not.
So you pop the hood to check the transmission fluid level. Then you notice it: A big mountain of corrosion on the battery terminals. You’ll have to take care of that, but it can’t have anything to do with the transmission, right?
Wrong. In fact, there’s a good chance you just found your transmission problem. That’s because nearly every shift on today’s transmissions is operated electrically through a computer system. And that computer system gets its power from — you guessed it! — the battery.
Battery terminals like this can cause a wide range of transmission malfunctions. Even if your engine starts and runs fine you may have a low voltage problem that can affect your transmission's operation.
So an intermittent voltage drop from the battery can cause all sorts of interesting problems with transmission operation.
But wait; if the battery connections are bad, why does the engine start okay when you turn the key? Starting the engine should require a lot more current than the transmission, right?
That’s an interesting thing about electricity. Sometimes bad connections make contact okay when you apply a big load to the circuit; the extra current seems to push its way through the resistance, just like extra pressure might push through a kink in a garden hose. But the small amount of current required for the transmission solenoids isn’t enough to push through, so the transmission won’t operate properly.
The good news is the fix for this is easy… and relatively cheap. A good battery service, including cleaning the terminal ends, will usually be all that’s necessary to correct the problem permanently. If the connections are too bad, you may need to have the terminals or cables replaced. But either way, once it’s done, you’re back in business.
Don’t Try This at Home! Cleaning the battery terminals is easy; you can do it yourself, right?
Careful, now. You could be opening a can of worms.
First off, those computer systems have memories. Disconnecting the battery could wipe those memories, causing you all sorts of driveability problems while the systems relearn their behaviors.
And on some cars, the radio could have a theft deterrent system. Disconnecting the battery could disable the radio until you enter the theft code. If you don’t know the code, the radio will have to go back to the manufacturer to be reset. That’s why most shops use a memory saver when disconnecting the battery. The memory saver applies a low voltage to the system to keep the memories alive while you have the battery disconnected. If you aren’t equipped to save the memories, your best bet is to leave servicing the battery to the professionals.
Your local ATRA Member shop is equipped to service your car’s battery, including cleaning and repairing any issues with the terminal ends. And they’ll be able to check your transmission afterward, to make sure it’s working properly.
To find an ATRA Member shop near you, click the Shopfinder link.
If you have any questions you can e-mail them to ATRA's Technical Department through the Technical Services page or call 1-866-GO-4-ATRA (1-866-464-2872)
More Transmission Problems articles available.