Q: Car independently downshifts on startup

asked by on August 19, 2016

When I was slowing down, my car independently started downshifted very hard. I never shifted the transmission. This problem stopped happening for about a week and then started up again, This time the check engine light came on, but was not flashing. Now the problem is constant, both the hard downshifting and the check engine light stays on. I put it in neutral now when slowing down and this avoids more strain on the transmission. But when I shift into Drive, it hard shifts. Also, my car has a sealed trans fluid unit, so it’s probably not the fluid. I will be taking it to be serviced, but before doing so I want to find out what is wrong with it. What is your assessment of these problems?

Transmission Fluid Service $140.08 - $502.73 Get a Quote
Check Engine Light is on Inspection $94.99 - $114.99 Get a Quote

There seems to be a problem inside the transmission and the code that has turned on the Check Engine Light may point to it. Other vehicles having similar symptoms have had faulty torque converter clutch solenoids or line pressure solenoids. I suggest hiring an experienced technician who can check the level and integrity of the transmission fluid and diagnose the trouble codes firsthand.

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


Experienced Mechanic?

Earn up to $70/hr

What others are asking

Need a diagnosis.
I would ask for help from one of the mechanics at YourMechanic. They have the experience and equipment to diagnose exactly why your vehicle will not start (https://www.yourmechanic.com/services/car-is-not-starting-inspection).
Car makes noise, automatic window switch, and wiper fluid sprayer not working
A car can make a wide variety of noises for a wide variety of reasons, especially under load, so I would recommend having the vehicle driven by a knowledgable technician so that a conclusive diagnosis of the noise (https://www.yourmechanic.com/services/car-is-making-a-noise-inspection) can...
Headlight went out twice
When you install the new bulbs, you have to take caution not to touch the bulb or get any type of grease or oil on them. If you do, you should wipe them off with alcohol. I would try a...
Power steering and power brake stop working
Both the power steering and power brake assist are powered by your power steering pump. I would start by inspecting the level and condition of your power steering fluid. It is located about mid-way down the driver side front of...
cylinder 4 misfire code reading?
It is helpful to state what kind of Dodge it is as some motors have pattern failures that other do not. Either way, there are a few simple tests that can be performed on any fuel injected motor to figure...
Car is jerking back and forth. P0171 and P0172 codes are on.
Hello. These symptoms suggest something is causing big swings in the fuel mixture when this occurs - quite possibly the O2 sensors (https://www.yourmechanic.com/services/oxygen-sensor-replacement) (pre-catalytic converter - 2 of them). P0171 (https://www.yourmechanic.com/article/p0171-obd-ii-trouble-code-system-too-lean-bank-1-by-andrew-quinn) is a "lean mix" warning, and P0172 (https://www.yourmechanic.com/article/p0172-obd-ii-trouble-code-system-too-rich-bank-1-by-blake-griffin) is...
i just replaced the camshaft timing senser bank 1 but it still does not have power when excellerating.
Hi there. The warning light and error code that indicates a camshaft timing sensor error is not always caused by the sensor itself. In fact, more often than not, the problem is with the electrical harness that connects the sensor...
2012 genesis 3.8 shifts hard. What cost am I looking at to replace transmission
The shift issue should be diagnosed first especially considering the low miles on the transmission. It would be unusual for a transmission with only 78,000 miles on it to require total replacement (versus on the vehicle service). Anytime you are...
Coolant in gas tank
Hi there. This is a very difficult question to answer, as we don't know how long the engine was exposed to coolant in the fuel system before it was noticed. In most cases, the damage that will be done is...

Related articles

P0103 OBD-II Trouble Code: Mass Airflow (MAF) Circuit High Air Flow and High Voltage Output
P0103 Trouble code definition Mass Airflow (MAF) Circuit High Air Flow and High Voltage Output The Code P0103 code is often associated...
P0084 OBD-II Trouble Code: Exhaust Valve Control Solenoid Circuit (Bank 2)
P0084 P0084 trouble code definition P0084 is a general code indicating an issue with the exhaust valve control circuit on the bank 2 side of the engine. This code is similar to P0085 and P0086. The engine also has a...
How to Install a Camshaft
Over Over the years, engines (https://www.yourmechanic.com/article/how-a-modern-engine-works) have evolved in so many ways. Most of the changes or improvements that have been done revolve around creating better performance and fuel economy, without making the engine larger. One of the biggest changes...