Transmission problems are unbelievably expensive, and often difficult to figure out. The gearbox is a very complicated device with countless moving parts that must work together in unison. So if the transmission isn’t shifting while you’re accelerating, you could have a very expensive transmission problem on your hands.
What Transmission Do I Have?
Transmission fluid
Transmission fluid is the lifeblood of your gearbox. In order to move you down the road, your automatic transmission has to convert the rotational energy coming from the engine into hydraulic pressure. The pressurized transmission fluid is then able to move parts around inside the transmission which enables gear changes to happen.
If your transmission fluid level is too low, or the fluid itself is dirty, there won’t be enough hydraulic pressure to change gears as you accelerate. To avoid this, check your transmission fluid level regularly and have the transmission serviced according to schedule. For more information on how often you should change your transmission fluid, click here to read our handy guide on the subject.
ECU or TCM problems
Modern vehicles are almost entirely controlled by computer. If your car won’t shift while you’re accelerating, then it is very likely that either the main engine control unit/ECU or transmission control module/TCM are having an issue. These computers interpret data from many different sensors around the vehicle, then do everything from adjust the air/fuel ratio in the engine, to determine which gear the transmission should be in at any given time. If one of these little supercomputers isn’t functioning correctly, your vehicle won’t either.
Failed sensors
Since the engine and transmission computers require sensor data in order to do their job, having a bad sensor will certainly cause your transmission not to shift. One of the most common sensor failures related to this issue is the vehicle speed sensor/VSS. This little gizmo tells the computer how fast the vehicle is going by reading how fast the output shaft on the transmission spinning. If there’s an issue with the sensor, the TCM won’t command an upshift when you’re accelerating, because it can’t figure out how fast the vehicle is going.
Failed solenoid
A transmission solenoid is responsible for directing the flow of pressurized transmission fluid down the right chambers inside of the valve body. Whenever the transmission computer/TCM decides to change gear, it sends an electrical charge to a coil wire surrounding the plunger mechanism inside solenoid. This causes it to open or close, allowing pressurized hydraulic fluid/ATF down the right chamber to actuate a gear change. If you’re having solenoid problems, your transmission will not be able to shift gears when it needs to.
What Transmission Do I Have?
Failed transmission clutch
Yes, even an automatic transmission has a clutch. Well, multiple clutches to be precise. There are actually small, round discs that are coated in a friction material that allows them to grab onto the flat steel discs that they are sandwiched together with. These clutch packs are operated by hydraulic pressure, and are responsible for engaging and disengaging gears. If there is an issue with one of the clutch packs, then your transmission will not be able to shift while you’re accelerating.
