Why is my automatic transmission not shifting properly?

In most cases, improper shifting stems from fluid issues, worn internal parts, or problems with the transmission’s control system. A quick check of fluid level and condition, plus any available diagnostic codes, can guide the next steps and help prevent further damage.

Common causes of improper shifting

The following list covers the most frequent reasons a gearbox fails to shift smoothly. While some fixes are simple, others require professional service.

• Low transmission fluid level or leaks


• Dirty, degraded, or incorrect transmission fluid


• Worn or damaged clutch packs, bands, or gears


• Faulty valve body or shift solenoids


• Torque converter problems


• Overheating or cooling system issues


• Transmission control module or software problems


• Sensor issues or incorrect wiring, including misadjusted linkages on older cars


• Clogged filter or screen impairing fluid flow


• Internal mechanical damage from wear or prior failures

These issues manifest differently across models, but fluid problems and electronics often top the list. Addressing them promptly can prevent more serious damage.

Common symptoms of shifting problems

Knowing the signs helps you assess severity and communicate clearly with a technician.

• Shift delays, hesitation, or gears not engaging


• Harsh or late upshifts or downshifts


• Slipping out of gear while driving or during acceleration


• Transmission warning light or check engine light on


• Unusual noises (clunking, whining, grinding) when shifting


• Fluid leaks, burnt smell, or fluid discolored by heat


• Vehicle won’t move in any gear or sticks in neutral

If you notice any combination of these symptoms, treat it as a priority. Do not ignore warning lights, as continuing to drive can damage the transmission further.

How to diagnose shifting problems at home

These at-home checks help narrow down likely causes before you visit a shop. They emphasize safety and non-destructive assessment.

1. Check transmission fluid level and color when the engine is warm and the vehicle is on level ground. Low or burnt-smelling fluid can indicate leaks or overheating.


2. Look for signs of leaks under the car and inspect the transmission pan for metal shavings or debris.


3. Consult the owner's manual for the correct fluid specification and whether a filter replacement is advised.


4. Scan the vehicle with an OBD-II reader for transmission-related codes (common ones include P0700 and related gear-control codes). Save any codes for the shop.


5. Test drive in a safe area to note when shifts occur and whether the issue happens in one gear, all gears, or only under load or acceleration.

Note that many transmission diagnostics require specialized tools and knowledge. A fluid issue or code can point you to the right next steps, but deeper repairs may require professional service.

What to do next

After initial checks, decide on a plan of action. The following steps help you determine whether to perform maintenance, part replacements, or professional service.

• If the fluid is low, top up with the manufacturer-specified transmission fluid and inspect for leaks. Do not drive far with low or burnt fluid.


• Replace transmission fluid and filter if due for servicing, especially on high-mileage vehicles or if the fluid is contaminated.


• Repair leaks promptly by addressing seals, gaskets, or cooler lines to prevent fluid loss and contamination.


• Consult an experienced shop for advanced testing (pressure tests, solenoid testing, valve body inspection, or transmission removal) if symptoms persist.


• If the vehicle is under warranty or subject to a recall, consult the dealer for covered work.

Timely evaluation can prevent catastrophic damage, which is often more expensive than routine maintenance.

Maintenance and prevention tips

Regular care helps keep transmissions shifting smoothly and extends life. Consider these best practices.

• Follow the manufacturer’s maintenance schedule for transmission fluid changes and filter replacement.


• Use the correct spec fluid; avoid unverified or universal fluids that may not meet your transmission’s requirements.


• Maintain the cooling system to prevent overheating that can degrade fluid and components.


• Repair leaks promptly and check for contamination from faulty seals or lines.


• Avoid towing beyond capacity; use a transmission cooler if you regularly tow heavy loads.


• Address check-engine or transmission codes promptly with routine scans to catch issues early.

Consistent maintenance helps prevent shifting problems and minimizes costly repairs by keeping fluid clean and at the right level.

Frequently asked questions

Will a transmission fluid flush fix shifting problems?

In some cases, a flush and fluid replacement can resolve shift hesitations, especially if fluid is old or contaminated. If the problem stems from worn clutches, valve body damage, or faulty solenoids, a flush alone won’t fix it and more extensive repairs are likely needed.

Is it safe to drive with a transmission problem?

Driving with a transmission issue can cause further damage. If you notice slipping, gear loss, or warning lights, limit driving and seek professional diagnosis as soon as possible. In some cases, towing may be the safer option to avoid additional harm.

Summary

Automatic transmissions shift best when fluid is clean, temperatures are controlled, and internal components like clutches, valves, and solenoids function correctly. When shifting becomes erratic or fails, start with fluid checks, review diagnostic codes, and seek professional evaluation. With timely maintenance and targeted repairs, most shifting problems can be resolved without replacing the entire transmission.

Can you fix a slipping transmission without replacing it?

Yes, a slipping transmission can sometimes be fixed without full replacement by first addressing potential simple causes like checking and changing the fluid, or by repairing or replacing smaller components like solenoids, bands, or a leaking seal. However, if the internal friction material from clutch plates is worn or other parts are damaged, a complete replacement or professional rebuilding may be necessary. 
What you can try

• Check transmission fluid: A low, dirty, or burned fluid level can cause slipping. Check the level with the dipstick and top it off if needed. 
• Change the fluid and filter: A fluid change is a common first step that can resolve issues caused by contamination. 
• Address leaks: If you find a leak, fix the faulty part, such as a loose seal or a bad pan gasket. 

This video shows how to check and refill transmission fluid: 1mHowYouCanDoItTooYouTube · Jan 1, 2019
When professional help is needed

• Internal damage: If simple fixes don't work, a professional mechanic can properly diagnose underlying issues like worn-out clutch plates or damaged gears. 
• Solenoid or sensor issues: A faulty solenoid or sensor can cause slipping. A mechanic can test and replace these parts. 
• Worn bands: In automatic transmissions, worn or broken bands can cause slippage and require professional attention to fix. 
• Costly repairs: If internal components are severely damaged, the transmission may need to be rebuilt, which involves taking it apart to clean, inspect, and replace worn parts, or a full replacement. 

Before seeking help

• Don't delay: A slipping transmission should be addressed promptly to prevent further damage. 
• Avoid certain additives: Some additives, like stop-leak or seal conditioners, can create more problems and make a future repair more difficult or expensive. 
• Consult a professional: A qualified transmission specialist can properly diagnose the problem and recommend the best course of action, whether it's a simple fix or a more involved repair. 

Why are my gears not shifting smoothly?

Difficulty shifting gears can be caused by various issues, ranging from low transmission fluid to more serious problems like worn gears or a faulty transmission control module. Transmission fluid is essential for lubricating and cooling the transmission components, as well as enabling smooth gear shifts.

What sensor would cause a transmission to not shift?

A failed vehicle speed sensor (VSS) or transmission range sensor (TRS) (also called the transmission position sensor) can cause a transmission to not shift gears. The VSS provides data on vehicle speed, which is critical for proper shift timing, while the TRS tells the car's computer which gear the driver has selected, such as 'Park' or 'Drive'. A faulty VSS may prevent upshifts, while a faulty TRS can cause a car to not engage a gear at all, even if the shifter is moved. 
This video explains the symptoms of a failing transmission speed sensor: 50sMaxTheCarGuyYouTube · Nov 5, 2023
Vehicle Speed Sensor (VSS)

• Function: The VSS monitors the vehicle's speed and sends this information to the transmission's control module to determine the correct time to shift. 
• Symptom of failure: If the VSS fails, the transmission may get stuck in a lower gear because it doesn't know the car is moving fast enough to upshift. 

Transmission Range Sensor (TRS)

• Function: The TRS, also known as the transmission position sensor, tells the car's computer which gear the driver has selected (Park, Reverse, Neutral, Drive, etc.). 
• Symptom of failure: A bad TRS can cause a variety of problems, including: 
  • The car will not start even if the key is turned. 
  • The car won't engage in the gear you've selected, even though the shifter is in the correct position. 
  • The gear indicator on the dashboard doesn't match the gear you have selected. 

This video explains the symptoms of a failed transmission range sensor: 56scar PROblemsYouTube · Feb 21, 2023
Other related sensors

• Throttle Position Sensor (TPS): A faulty TPS may not send correct information about how much the accelerator pedal is pressed, which can interfere with the transmission's shift logic. 
• MAP (Manifold Absolute Pressure) Sensor: This sensor provides data about engine load. An incorrect reading can affect transmission shift timing. 

How to diagnose the issue

• Check for warning lights: A faulty sensor can trigger the Check Engine Light or a separate transmission warning light. 
• Use an OBD-II scanner: A mechanic can use a scanner to check for specific diagnostic trouble codes (DTCs) related to the transmission and sensors. 
• Monitor gear selection: A scanner can also be used to monitor the signals the transmission range sensor is sending to ensure they correspond to the physical gear selection. 

This video demonstrates how to diagnose transmission problems: 52sRatchets And WrenchesYouTube · Oct 20, 2016

What happens right before your transmission goes out?

You can tell your transmission is about to go out by listening for unusual noises like grinding or whining, and by observing issues like slipping gears, delayed or harsh shifting, or hesitation when accelerating. Other signs include a burning smell, transmission fluid leaks, and the illumination of the "Check Engine" light. 
Symptoms of a failing transmission

• Unusual sounds: Listen for grinding, whining, clunking, or humming noises. A loud or rough sound when shifting gears is a major warning sign. 
• Shifting problems:
  • Slipping: Your car may feel like it's shifting gears on its own, especially when accelerating. 
  • Hesitation or delay: There may be a noticeable delay when shifting into gear or when the engine revs before a gear change. 
  • Rough or hard shifts: Shifts may feel jerky or harsh instead of smooth. 
• Fluid issues:
  • Leaking fluid: A red or brown puddle under your car could indicate a transmission fluid leak. 
  • Burning smell: A sweet, burning smell often points to overheating transmission fluid. 
• Warning lights: The "Check Engine" light or a dedicated transmission warning light can come on to indicate a problem with the transmission. 
• Performance issues:
  • The vehicle may be slow to accelerate or feel sluggish. 
  • The car may not move when you put it in gear and press the gas pedal. 

What to do
If you experience any of these symptoms, have your vehicle inspected by a professional mechanic as soon as possible. Driving with a failing transmission can lead to more severe and costly damage.