Skip the auto shop - Our mechanics make house calls

Q: Auto transmission downshifting to lower gear when decelerating causes the car to lurch. Why?

asked by on

When decelerating through 20 mph the auto transmission downshifts to a lower gear than needed causing the car to lurch like hitting the brakes suddenly. I feels likes downshifting into 1st gear at 20 mph when it should be downshifting into 2nd or 3rd gear.

My car has 115000 miles.
My car has an automatic transmission.

A: This may be a result of low transmission fl...

This may be a result of low transmission fluid or potentially a faulty transmission control module. A faulty transmission control module may cause a delay in acceleration or erratic shifting of gears. The transmission control module has various sensors such as vehicle speed sensors, wheel speed sensors, throttle position sensors, turbine speed sensor, and transmission fluid temperature sensors that all direct information to it in order for it to perform it’s function. Other components controlled by the TCM are components such as a kick down switch, traction control system, and cruise control module. Any of these may also affect the way the transmission control module performs and controls the transmission and the shifting of your vehicle. In your case it sounds like you may have a faulty kick down switch causing the transmission to downshift prematurely. I would suggest having a professional from Your Mechanic come to your location to properly diagnose your transmission shifting problem.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Intelligent key light

The intelligent key light is controlled by the ignition system for the anti-theft system to be active. There are many complaints of the problem caused by a steering lock system problem, which may need replacement to prevent this issue from...

Q: Will putting a different tire size cause my car to shake or my tires to wear out quick and uneven?

Hi there. The engineers that design vehicles do so by making sure each part is precisely sized to match others - so the vehicle operates safe and efficiently. This includes the wheel and tire overall width and circumference. What you're...

Q: left front and right rear brakes locked up while driving

From the sounds of things, a fault with the ABS system seems the most likely at this point as the original cause. A few other causes would be a brake caliper that had seized or a mechanical brake issue, such...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...