6 Reasons Automatic Transmission Slipping When Accelerating
With over a decade of automotive repair experience, I have observed that when this happens, the transmission doesn’t shift or engage the gears correctly, and its speed fails to correlate with that of your engine. It just gurgles and revs up but barely reacts as it should.
Here is a list of the 6 Reasons Automatic Transmission Slipping When Accelerating that you should be aware of:
- Drain Out Overfilled Transmission Fluid
- Pour In Transmission Fluid When Low
- Flush And Change Dirty Transmission Fluid
- Change The Transmission Filter When Clogged
- Replace Any Bad Transmission Solenoid
- Check The Electronic Throttle Body And TCM
Let’s explore more details about the problem and what you can do to resolve it efficiently.
Symptoms of Automatic Transmission Slipping when Accelerating
From what I’ve noticed over the years, a slipping automatic transmission tends to rev up the engine and move slowly or not at all during acceleration. Among other common symptoms, there are:
- The engine making a loud, gurgling noise while revving
- The clutch is not responding
- Engine shifting hard and not staying in gear
- A burning smell
- Engine not reversing
- Sudden loss of power
- Check engine light is coming on
Why Does Automatic Transmission Slip When Accelerating and How to Fix It?
As I said earlier, transmission fluid often plays a big role when the automatic transmission pops out of gear while driving or accelerating. Let’s find out why that is and what other causes you should look into.
#1- Drain Out Overfilled Transmission Fluid
When you overfill, the transmission fluid may foam up and cause cavitation in your automatic transmission.
Fluid cavitation is when a high amount of transmission fluid causes significant changes in the overall fluid pressure. When this happens during acceleration, you will see the symptoms of bubbles forming in large amounts.
And what I’ve seen results from this, besides an erratic shifting, is oil starvation, which eventually leads to internal transmission damage.
Here’s what I’d suggest you do to correct overfilled transmission fluid.
- Step 1: Park your car somewhere with a level surface so you’re accurate with the fluid reading.
- Step 2: From the transmission port, take out your car’s dipstick to check the fluid indicators. You may refer to your service manual when unsure about the evaluation.
- Step 3: Now, you must drain the extra fluid. To do this, the easiest way I figured, is to use the transmission’s drain port.
- Step 4: After the draining, repeat step 2 to ensure your car is on the correct fluid level.
Do you have a manual transmission slipping when accelerating? You might want to try these methods instead.
#2- Pour in Transmission Fluid When Low
Like overfills, low fluid levels can also cause your automatic transmission to slip as you accelerate.
When your transmission is low in fluid, the oil pump has to run dry. And when that happens, the torque converter responsible for creating the pressure also runs dry, leaving no hydraulic pressure on the solenoid.
Besides miss shifting your transmission, this leads to faster wearing of the friction plates and the clutch bands. It’s what I often find the culprit when someone drives in, complaining about their transmission making a whining noise.
As you’ve guessed, the fix to low transmission fluid is to fill it up at the correct level. You can try the dipstick method shown in the previous section for accurate checking and filling. Or, you can keep pouring until it spills over the fill hole if you have no dipstick.
#3- Flush and Change Dirty Transmission Fluid
When diagnosing automatic transmission issues, I learned several things that can go wrong with the transmission fluid’s consistency. Dirt, grime, or worse, metal flakes can contaminate it to damage the transmission’s internals to wear fast.
You can suspect this to be the case while accelerating and miss-shifting when you find the fluid has a burnt smell or it’s gone stark black. After all, these are indications that your transmission’s hydraulic system isn’t building enough pressure to shift the gears.
While changing the contaminated transmission fluid entirely is your sole solution, I’d suggest doing a proper flush with a new filter and nutrients beforehand.
Here’s a video to guide you on how to do it properly.
#4- Change the Transmission Filter When Clogged
Your car’s transmission filter sits above the transmission pan to catch any excess fluid. It also sieves out any contaminants before circulating the lubricating fluid to the main transmission body.
As you can guess, it can get clogged easily while collecting dirt and debris over time. When this happens, it can no longer pull the required transmission fluid through the transmission oil pump consistently. As a result, the solenoid fails to receive enough liquid to keep itself operating.
From what I’ve seen, slipping transmission during acceleration is only one of the many problems it entails. For example, your car won’t budge at all no matter how much you try the accelerator pedal, leading you to think there’s a severe engine issue.
As for the solution to this problem, changing the filter is my only viable option. I won’t suggest cleaning or repairing, as it may end up being costlier in the long run due to the likelihood of future occurrences.
Here’s how I proceed to change an automatic transmission filter.
- Step 1: Before anything, you should first drain the old fluid. Be sure to drain it entirely.
- Step 2: Access the filter underneath your car and remove the pan by removing the bolts. Then clean the pan, magnets, and any sealants.
- Step 3: Now install the new filter and gasket in the reverse order you went for the disassembly and reattach the pan.
- Step 4: Refill the transmission with new fluid, and check the level using the dipstick. Finally, test the gears to ensure smooth shifting.
#5- Replace Any Bad Transmission Solenoid
Transmission solenoids are found inside the transmission. Its job is to direct the hydraulic fluid into the valve body to ensure the engine engages the correct gear.
This solenoid won’t send the hydraulic pressure into the valve body when it goes bad. Or in other words, it won’t let the transmission shift into the proper gear, causing it to slip as you try to accelerate.
From an experience perspective, I can tell you attempting repairs on a bad transmission solenoid isn’t helpful in the long run, either cost-wise or safety-wise. Replacing it with a new one is the only thing I’d suggest here.
However, I’d also recommend leaving this job to a professional. This is because the replacement involves strictly following a diagram and wiring pattern for specific vehicles.
#6- Check the Electronic Throttle Body and TCM
Some vehicles have an electronic throttle body controlled by a sensor in the throttle pedal.
If the communication between the electronic throttle body and the TCM (transmission control module) gets disrupted, it can cause the transmission to slip or not shift correctly. This can happen due to a worn or broken dial in the throttle body or a fault in the TCM.
Shifting up and down gears abnormally or skipping gears altogether, like going from second gear to fourth gear without shifting to third gear, are some signs I’ve noticed when this occurs.
Depending on the situation, repairing the throttle body or replacing the TCM should solve this issue. Sometimes, just cleaning and adjusting the connector teeth is all it takes, but very often, it will require a complete replacement. So, you’d better consult a professional before trying out anything yourself.
Conclusion
To recap, Here is a list of the 6 Reasons Automatic Transmission Slipping When Accelerating that you should be aware of:
- Drain Out Overfilled Transmission Fluid
- Pour In Transmission Fluid When Low
- Flush And Change Dirty Transmission Fluid
- Change The Transmission Filter When Clogged
- Replace Any Bad Transmission Solenoid
- Check The Electronic Throttle Body And TCM
You’ve probably noticed that transmission fluid is mainly responsible for automatic transmission slipping when accelerating. That’s why I’d recommend checking the transmission fluid for any irregularities at least twice a year or whenever you suspect a problem.
Remember, taking on issues such as overfilling, leaking, or low fluids in transmission can save you a lot of time and money before things take a difficult turn.
Video References
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Certification: BSc in Mechanical Engineering
Education: Mechanical engineer
Lives In: 539 W Commerce St, Dallas, TX 75208, USA
Rasel is an auto mechanic student and writer with over half a decade of experience in the automotive field. He has worked with top automotive brands such as Lexus, Quantum, and also owns two automotive blogs autocarneed.com and taxiwiz.com.