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.

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

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  • Home
  • Questions
  • Auto transmission downshifting to lower gear when decelerating causes the car to lurch. Why?

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: All of the dash lights and gauges flash, and then the car dies

Have the main integrated fuse relay box checked for connection issues. The fuse box on these vehicle have been known to cause stalling issues along with other erratic electrical issues. Contact a dealer to see if your vehicle may have...

Q: ABS and Brake warning lights constantly on

The ABS and Brake light on will store a code in memory. You need to have the stored codes cleared and then road test to verify the codes return and diagnose the codes. You may have a bad speed sensor...

Q: o2b1s1= 1.95 V , o2b1s2=0.70 V , P0420

The upstream oxygen sensor appears to be out of range. The expected value should be between 0.2 and 0.9 volts with a frequency of 1 to 5 Hertz. Your report shows 1.9 volts. I would first look at a real...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
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...