The most common reasons behind the speedometer not working and transmission not shifting are a damaged speed sensor, bad wiring, blown fuses, low transmission fluid, and faulty ECU.
Keep reading this article to find out more about these issues in detail and learn how to fix a transmission that won’t shift and your car back to normal again.
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Speedometer Not Working And Transmission Not Shifting [5 Easy Fixes]
The transmission not shifting while driving and the speedometer not working is dangerous and can lead to accidents. If you’re in that situation, you need to address the issue as early as you can. Here are the most common reasons behind this problem:
Note: You can also read how to fix Automatic Transmission not shifting into 4th gear.
1. Damaged Speed Sensor
If you’re wondering why my transmission won’t shift and the speedometer won’t work, the most likely reason behind it is a damaged speed sensor. So, can the speed sensor cause shifting problems?
Your transmission and speedometer rely on the speed sensor to function properly and they will fail if the speed sensor goes bad.
The speed sensor is typically located at the transmission of the car and it measures the rotational speed of the transmission to figure out how fast the car is traveling.
The speedometer collects the data from the speed sensor and displays it to give you an accurate reading of the current speed. Cars with automatic transmissions also use it to figure out when to shift. When it goes bad, it affects both the speedometer and transmission.
The speedometer malfunctions when it has prolonged exposure to different elements like sand, water, or salt as it’s located outside the car. The sensor can crack when it happens and it can allow dirt and debris to get in and give completely inaccurate readings.
It can also happen if you leave the transmission fluid in your car too long without driving it. The transmission fluid can become thick and clog some of the important parts of the speed sensor.
Along with the speedometer and transmission not working, some other symptoms of a faulty speed sensor are:
- The check engine light will be on.
- If your car has cruise control, it won’t work.
How to fix the transmission not shifting when the speed sensor is damaged? You need to replace the speed sensor with a new one. It’s easy to locate the speed sensor on your car as you already know that it’ll be close to the transmission.
Replacing it is an easy job if you have something to lift your car. Follow these steps to replace the speed sensor in your vehicle:
- Turn off the engine and disconnect the battery.
- Get your raised with a jack stand.
- Locate the speed sensor in your car.
- Place a pan under the sensor as transmission fluid could leak from it.
- Disconnect the wiring harness that is connected to the sensor.
- Unscrew the fastener that’s holding the speed sensor in place using a torque wrench.
- Pull out the old sensor and put the new one in its place.
Do the steps in reverse and put everything back together to seal the new sensor in its place. It’s not an expensive repair if you decide to do it yourself as the part itself only costs between $20 to $50 for most cars.
2. Bad Wiring
Before you go ahead and replace the speed sensor, it’s a good idea to check if the wiring to the speed sensor is alright. The wiring harness is located close to the transmission and connected to the speed sensor.
Check if there’s power flowing through the wiring harness using a multimeter. If it reads close to 12V, that means the wiring is good. But if the reading is close to zero or low, that means it’s not getting enough power.
The wires are also prone to damage when they got exposed to water or other elements when you drive the car and can short out. The wiring harness can also get corroded with time after coming in contact with salt or snow.
If the wiring harness is getting some power, it means there’s a good chance that the wiring harness isn’t reaching its full potential because of corrosion. Clean it and see if that solves the problem.
But if you get absolutely no power to the wiring harness, that means there’s a break somewhere. You can either identify the break and replace the wire or completely replace the wiring harness to make sure the speed sensor gets power and fixes the speedometer and transmission in your car.
3. Blown Fuses
When there’s a short in the power, it can draw too much current and lead to a blown fuse. The most common victims you should check if the wiring has shorted are the transmission fuse and the odometer fuse.
These fuses are normally located in the engine bay or the driver’s side of the vehicle. You can check if they have power with a multimeter or a simple visual inspection to see if the link is broken.
If you find that any of the fuses are blown during your inspection, replace them with new ones. It’s a cheap fix if replacing the fuse solves the problem. But if it keeps blowing, there are other issues in the car like damaged wiring or ECU.
4. Low Transmission Fluid
Though transmission are speedometers are different components, a problem in the transmission can easily lead to a problem in the speedometer. And what causes the transmission to not shift? Having low or dirty transmission fluid causes shifting problems in cars with both automatic and manual transmissions.
You need to pop the hood to check the level of transmission fluid in your car. Pull the dipstick out, wipe it with a towel and then insert it back in all the way down. Then pull it out and check the level of your transmission fluid.
Make sure your car is on a level surface when you’re checking the transmission fluid. Otherwise, you may get the wrong reading. While you’re at it you should also check the quality of the transmission fluid.
Dirty transmission fluid can cause all sorts of problems like losing viscosity and not lubricating properly even if the level of transmission fluid is good. Any leak in the system can also cause the transmission fluid to run out quickly.
How to fix the automatic transmission not shifting? Drain the transmission fluid in your car if it has been a while since you changed it and the current fluid has gotten old and dirty. Add the fluid if you’re running low on it.
If the transmission fluid keeps getting to a low level because of a leak, it’s a good idea to take your car to a mechanic. He’ll identify where the leak’s coming from and tell you how to proceed.
5. Faulty ECU
If you’ve already checked the first four potential causes and still wondering why is my transmission having trouble shifting, the next thing you should check is the ECU (Engine Control Unit).
The ECU is the brain of your car’s computer and it’s connected to all the sensors and electrical components in your car. When the ECU goes bad, it can’t communicate properly with the sensors and gives a wrong output even when the sensor is working well.
You have to replace the faulty ECU with a new one. Unfortunately, ECUs are expensive and it can cost a lot of money to replace them. You can expect to pay at least over a thousand dollars to replace the ECU in most vehicles.
Is it okay to drive with a damaged speed sensor?
It’s not good to drive with a damaged speed sensor as it can make the transmission go bad and lead to an expensive repair. There are also safety risks as you won’t be able to shift the transmission properly.
What causes ABS light on transmission not to shift?
The most common reason behind the transmission not shifting and the ABS light being on is a failing speed sensor. It can also happen when the carrier bearings on the rear end have worn out.
Why is my gear shift not moving?
The main reason why your car won’t shift gear is because of the shift lock mechanism that only allows the car to shift out of parking mode when it detects a driver with a foot on the brake.
What are the signs of a transmission sensor going bad?
The common signs of the transmission sensor going bad are your car fails to shift out of neutral or park, gets locked in a single gear, shifts to the wrong gear, and stalls the engine.
You longer have to wonder why my transmission won’t shift after completing this article. Now you know the typical reasons behind the speedometer not working and transmission not shifting and how you can fix them.
Refill your transmission fluid in regular intervals and maintain your car properly to avoid facing this issue. Drop a comment below if you have any more questions about failing speedometers and transmissions.