There is no doubt that Kia had a poor reputation two decades ago, in part due to frequent automatic transmissions problems. Since then, Kia has made a 180-degree turn.

Models such as Sportage, Rio, Telluride, Stinger, Sorento, Optima, Soul, Sedona, Forte, K900 are now some of the most reliable vehicles on the market with very few transmission problems. 

Are Kia Transmissions Reliable?

Overall, Kia transmissions are quite reliable. The majority of Kia transmission problems such as transmission won't engage, transition slips, delayed shifting, transmission bangs into gear, no drive or reverse gears, stuck in limp mode, are often caused by low transmission fluid. These symptoms may also be due to problems with the transmission control module which in some cases can be fixed by having the dealer perform a software update. 

If you are experiencing any of these symptoms, check the transmission fluid level immediately and correct it if needed. Also, call any Kia dealer and ask if there are any Technical Sevice Bulletins (TSBs) or software updates for the transmission. 

With that said, we still come across Kia vehicles that have automatic transmission problems, especially vehicles that aren't maintained or that are used for towing.

Kia Automatic Transmission Problems

Valve Body

Let's take a look at some problems and common causes of Kia automatic transmissions. 

Shift flares and delayed gear changes

KIA cars that use an A4CF 4-speed automatic transmission have a common gear shift issue, which involves shift flares or slipping when going into 2nd, 3th, and 4th gear.

In some cases, there will be a prolonged pause followed by a clunk when selecting reverse. Usually, any of the symptoms will be more prominent while the car is cold. This can trigger a check engine light, so there will be a corresponding code in DTC memory.

Possible causes and solutions

  • Pressure drop inside the valve body, as a result of leaking solenoids. Being an issue that usually happens at a gradual rate, the symptoms will be more apparent when the vehicle is cold. As this is a prevalent problem, there are sets with uprated solenoids available.  
  • Faulty internal harness, which causes interference in communication between TCU and solenoids. Unlike leaking solenoids, this will cause intermittent and sudden issues and will trigger a check engine light with solenoid related codes.

Erratic shifting and jumping into neutral

Vehicles that use an A4CF 4-speed automatic transmission can suffer from issues that range from jumpy gear shifts to sudden and uncontrolled shifts to neutral while driving.

When this happens, the driver will not be able to engage any gear, despite selecting the drive or reverse. These issues usually trigger a check engine light, meaning there will be a corresponding code in DTC memory.

Possible causes and solutions

  • Faulty input or output speed sensor, which offsets the shift procedure and causes misleading solenoid related codes. As deciding on which of these two sensors is causing the problem is not a straightforward task; the most efficient way of dealing with this issue is to replace both of them.

Erratic and failed gear shift

Kia Sorento that uses a RE5R05A 5-speed automatic transmission, can suffer from a range of shift issues, which include harsh shifts and failed gear changes. Any of these problems may occur sporadically or be present all the time. This will usually trigger a check engine light, so there will be code stored in DTC memory.

Possible causes and solutions:

  • Faulty one or more solenoid valves. The usual ones to fail are those that operate the direct clutch, front brake, or input clutch. Each of them will trigger a different code, which will help narrow down the problem.
  • Wiring issues caused by damage or corrosion. This creates problems with communication between the TCU and solenoids. The resulting symptoms will be very similar to a failed solenoid, so double-checking the wiring and solenoid is a recommended step.
  • Broken or corroded connectors on the control board, resulting in sporadic loss of signal. While corrosion is easy to clean off, soldering broken connectors may be an unreliable solution. Instead, replace the board with a new or undamaged second-hand one.

Harsh or delayed gearshifts

KIA cars with A6GF1 6-speed transmission have a widespread issue with harsh or delayed gear changes.

In most cases, this problem will be intermittent and more present when the car reaches running temperature. A check engine light can also come on, which means there will be a code stored inside DTC memory.

Possible causes and solutions

  • Faulty transmission fluid temperature sensor, which will give false output readings. As this transmission is very sensitive when it comes to temperature, this will cause running issues and trigger a check engine light. Typical error codes range from P0711 to P0714. Checking both sensor and corresponding wiring will reveal the source of the problem.
  • These transmissions feature an adaptive learning procedure, meaning it will adjust shift patterns based on the driver’s habits.  When drivers with different driving styles use the same car, gear shifts may seem unusual. Resetting the learn-procedure may solve the issue.

Vibrations while accelerating or harsh shifting

Vehicles that use a D7UF1 7-speed dual-clutch transmission can suffer from several typical issues that include delayed response, strong vibration, and rattle during accelerations or while idling and harsh shifting. In most cases, the symptoms will be more noticeable when driving aggressively. These problems will not trigger a check engine light.

Possible causes and solutions

  • Worn dual-mass flywheel, which results in a metallic rattle on idle caused by an excessive play. When checking the flywheel condition, look for any free movement between the plates and replace them if there is any.
  • Overheated clutch assembly, which can cause the clutch to stick to the flywheel and result in delayed gear changes. One of the possible causes is a driving style that is too aggressive. In some cases, updating the TCU software to the latest version using a suitable diagnostic tool can help, as some vehicles have outdated software.
  • Broken or worn engine or gearbox mounts. This allows excessive movement, causing the engine and gearbox to jump when pulling off from stand-still.

Troubleshooting Kia Transmission Problems

If you Kia has developed transmission problems, we strongly recommend checking the transmission fluid level as soon as possible.

If the transmission fluid level has been corrected, but the transmission is not shifting correctly, read the fault codes from the Transmission Control Unit (TCU) with a Kia transmission scanner.

How to Check Kia Transmission Fluid Level

Kia Transmission Problems

  1. Park vehicle on level ground when possible. 
  2. Set the parking brakes and shifter in Park. 
  3. Pull the hood release and open the hood. 
  4. Locate the transmission dipstick. 
  5. Remove the dipstick and clean it with a clean cloth. 
  6. Reinsert the dipstick in the transmission. Ensure the dipstick is fully inserted then remove it. 
  7. Look carefully at the dipstick to determine the current transmission fluid level. The level should be between MIN and MAX marks for the COLD (lower) markings. 
  8. If the level is low, add transmission fluid level. 
  9. Drive vehicle for 15 minutes making sure to select all the gears manually. 
  10. Repeat the procedure once the transmission warm-up, but this time, the level must be between the MIN and MAX marks. 

Not all Kia vehicles have a transmission dipstick. If the dipstick is not present, the car will need to be raised on a lift, and the level can be checked via the fill hole. 

Read Transmission Fault Codes

Troubleshoot Kia transmission problems

The next step is to read fault codes from the transmission control module or what is known as the TCU. To read these codes, you will need a Kia Transmission Scanner. Basic code readers are not recommended because they will show a generic system or may not show a fault code at all.

  1. Park vehicle and turn off the ignition. Set parking brakes. 
  2. Locate diagnostic port under the dashboard, driver's side. 
  3. Plugin your OBD-II scanner then turn on ignition without starting the engine. 
  4. The scanner will turn on. Allow it to communicate with the vehicle. Select Kia then your particular. 
  5. Select Control Units then Transmission. 
  6. Select Read Fault Codes from the main menu.  

These steps work on all Kia vehicles 2000 an newer, including Kia Rio, Sportage, Telluride, Stinger, Sorento, Optima, Soul, Sedona, Forte, K900, Cadenza. All these models have an OBD-II diagnostic port under the dashboard on the driver's side. 

Make sure to use a Kia scanner that can read transmission codes. Generic scanners typically only read codes from Engine Control Unit (ECU), but you need a scanner that can read codes from the Transmission Control Unit (TCU) as well. 

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