While problems with automatic transmission are pretty rare, they’re not impossible. But the problem when an automatic transmission starts developing problems is that all the guides walk you through the problems for a manual transmission.
It’s a frustrating position to be in, which is why we wanted to bail you out with this guide. If you have a car with an automatic transmission and it won’t change gears, then keep reading to find out why.
Let’s get started!
7 Reasons Why Your Automatic Car Is Not Changing Gear
If you find that your vehicle’s automatic transmission won’t change gears, there are a few potential reasons. To help you sort through all the noise and try and figure out what’s going on with your vehicle we’ve highlighted seven of the most common reasons for you here.
1. Faulty Shift Interlock
The shift interlock is a component that an automatic transmission uses to let it know when it can go into drive and shift gears. You already know about this component even if you don’t know exactly how it works or if this is the first time you’re hearing the name.
The shift interlock is the entire reason you can’t start up your vehicle if you’re not in park or neutral. If it gives off a faulty reading, it can create all sorts of problems for your transmission, including the inability to shift gears or to get into gear.
2. Damaged Transmission Linkage
This is a pretty rare problem, but if you look at your transmission there’s typically a cable linkage that shifts it into different gears. While it’s rare, something can happen to this linkage.
If the cable snaps, then it won’t be able to shift gears as it should. Finally, newer vehicles might use an electronic transmission linkage, and these are actually more likely to fail than the old cable linkages.
3. TCM Problems
Of all the electrical problems your vehicle can have, this is one of the rarest. But rare doesn’t mean impossible. The TCM is the brain behind the transmission, and if the brain fails, nothing will work as it should.
Unfortunately, typically the only way to fix a TCM is to take the entire vehicle to a dealership where they have the computer programing to work on it.
4. Old Transmission Fluid
As transmission fluid ages it loses some of its ability to dissipate heat and lubricate components. Both things are critical to keeping the transmission in good working order.
So, if the transmission fluid is well past its service life there’s a chance that’s the reason the transmission won’t shift into a new gear. But with old transmission fluid, there’s also a good chance that there’s further damage so you might need a little more than a fluid flush to get your transmission to shift properly again.
Finally, the exact frequency you should change your transmission fluid varies, but it’s somewhere between 50,000 and 150,000 miles for most automatic vehicles. Check the owner’s manual to see what the manufacturer recommends for your specific vehicle.
5. Low Transmission Fluid
Your transmission doesn’t want to damage itself, and it often has a sensor that lets the TCM know when the transmission doesn’t have enough transmission fluid or pressure from the transmission fluid.
When this happens, the transmission will stop operating as it should simply so it doesn’t damage itself by trying to operate with little or no transmission fluid. But before you just go out and buy more transmission fluid to put in it, keep in mind that the old fluid went somewhere.
There’s likely a leaking gasket somewhere, and you’ll probably want to repair that before putting the new transmission fluid in.
6. Damaged Transmission Gears
Inside your transmission, tons of gears keep everything spinning. While these gears typically stay in pretty good shape, over time, they can start to wear down. If they wear down enough, it can keep your vehicle from shifting gears.
If that happens with your vehicle then you’ll likely need to send the transmission to a dedicated shop where they can rebuild it for you.
7. Failed Gear Selector Switch
If you can start up your car but you can’t get it out of park, then the problem might be with the gear selector switch and not the transmission itself. The gear selector switch is what you use to put the vehicle into gear.
But if the switch isn’t working the TCM doesn’t tell the transmission what gear you want to put the vehicle in, and you just stay in park. But while it’s a frustrating problem to have, the good news is that it’s typically far less expensive to fix than most of the other options on our list.
While transmission problems are complicated, there are a few simple troubleshooting tips you can try. These tips will rule out any possible easy fixes and ensure you’re not wasting any money by taking your vehicle to a professional mechanic.
Just keep in mind that these troubleshooting tips won’t help you fix every possible reason your automatic transmission won’t change gears, but it will rule out some of the possibilities.
1. Try shifting driving mode:
If you can’t get the vehicle into gear at all, try shifting to a different driving mode. If your vehicle has a sport mode or overdrive, see if it won’t go into gear if it’s in one of those driving modes. If it will, then the problem might be the gear selector switch or the shift interlock.
2. Check the transmission fluid:
Next, take a look at the transmission fluid. If there’s not enough in there do yourself a favor and top it off and see if that helps. But even if it does you need to figure out where the transmission fluid is going. There’s a good chance one of the gaskets has a leak.
Additionally, when you look at the old transmission fluid, pay special attention to the color. If the color still has a bright red hue, then it’s in good condition. However, if the transmission fluid has a burnt brown color, then it’s way too old and it’s time to flush it out.
But keep in mind that while a fluid flush might solve the problem, there’s also a chance that there’s another problem in addition to the old transmission fluid. It’s actually pretty likely since old transmission fluid doesn’t lubricate transmission parts as well as it should.
This causes the parts to wear down and eventually can damage them. This damage can prevent the transmission from shifting gears. The old transmission fluid might be what caused the problem, but even if you fix the cause of the problem you still have to fix the problem to get everything back in working order.
3. Check your On-Board Diagnostic Codes:
If you find the transmission fluid in good condition, it’s probably not the root of you problem. So your next step should be to look for any OBD (On-Board Diagnostics) codes, and for this you’ll need a scanning tool.
Most auto repair stores such as AutoZone will do this for free, but if you prefer to do it yourself, you can purchase your own OBD scanner for around $100.
These OBD scanners are great tools that will often reveal a lot about what is wrong with your vehicle, and hopefully in this case, the reason your automatic transmission is not changing gear.
4. Take your vehicle to a professional mechanic:
If none of the steps above have helped and you still can’t figure why your automatic car won’t change gear, you may want a professional mechanic to help troubleshoot your vehicle.
While we all agree that having to take your car to a repair shop can sometimes feel difficult, for some issues, it’s just best to take your vehicle to someone who has more experience. Even if you’re able to troubleshoot the issue yourself, many times the work is too complicated to do yourself.
If you can’t get your automatic transmission to change gears after reading through this guide, it’s time to get help from a professional mechanic. Don’t ignore the problem and hope it’ll go away either, but it’s more likely to get worse than to get better.
And now that you’ve ruled out some of the simple fixes with our guide, you can feel confident heading to a repair shop knowing you’re not wasting your time and money.
If you manage to change gear, but your car won’t move, then make sure to learn why by reading our article about it here.