14 Reasons Why Your Car Jerks When Slowing Down - Mechanic's Diary (2024)

Normally when you take your foot off the accelerator and step on the brake pedal to slow down, the car’s torque converter gradually downshifts the vehicle as the brakes slow the disc rotors. If your car starts jerking when slowing down or shuddering with deceleration, you likely have a serious problem that must be dealt with immediately.

When slowing down, this jerking can be traced back to a problem with the brake system or an imbalance in the engine’s fuel/air mixture. Though transmission problems, anti-lock brake problems, and other faults could also lurk.

To find the gremlin causing your car to jolt during deceleration, we’re going to have to plunge deep into the mysteries of how your car slows down with just the step of the brake pedal.

How Does A Car Slow Down

In a nutshell, many different things happen in the engine, transmission, and braking system when you take your foot off the gas pedal and press the brake. This starts with the brake calipers squeezing the brake pads on the rotors to slow the wheels via friction. Depending on your speed and how hard you brake, the anti-lock brake system might also engage in pulsing the brake pads without locking them up.

In the engine, the ECU adjusts the fuel/air mixture and the timing to produce less power. Meanwhile, in the transmission, the torque converter and the TCM make a concerted effort to change down the gear at the appropriate speed.

With so many processes happening in synergy, it’s easy for a small problem with one system to cause a major issue with another, causing the car to jolt, shudder, or jerk when slowing down.

4 Hidden Reasons Why Your Car Experiences Jerking During Deceleration

Anytime your car starts jerking when slowing down, your first thought should be that it’s coming from the anti-lock braking system. However, transmission issues and an imbalance in the engine’s fuel/air mixture are also top contenders for this gremlin.

Here are 14 factors that can cause your car to jerk when slowing down, along with suggested solutions to address them:

1. An Anti-Lock Braking System Problem

Anti-lock brake systems (ABS) have become common in a lot of vehicles, and the way they pulse the brake calipers can easily cause a jerking feeling especially if you’re braking hard or trying to decelerate from highway speed to make a short stop on an off-ramp.

The ABS actively monitors the wheel speed as you’re driving. When you step on the brakes, it estimates the risk of the brakes locking up and prevents a skid by pulsing the calipers on the rotors. This makes it possible for you to steer still to avoid road obstacles while still slowing down safely.

When the ABS controller has a fault or there are loose wires, it can cause the system to turn on and off intermittently. The ABS controller struggles to adapt to the sporadic conditions as the pads try not to lock up.

In a case like this, the jerking feeling when slowing down will usually cause the ABS warning light or the brake warning light to come on. If it’s a case of loose wires, you might notice the ABS warning light flash in time with the jerking feeling.

If you hook the car up to an OBD II reader, the most common codes for an ABS system malfunction are:

2. Car might have Warped Rotors

Warped rotors that have been deformed by overheated brakes or excess wear and tear can easily make the car jerk or vibrate when you slow down. This effect is most pronounced when you’re braking hard to slow down from highway speed to a stop light. Though as the state of the rotors worsens, you’ll start to notice the jerking and vibration during deceleration, even at low speeds.

If it’s the front rotors that are warped, the vibration when you slow down will also cause the steering wheel to vibrate. You might even hear a rasping or grinding sound. This is due to the normally flat surface deforming in places, causing it to make inconsistent contact with the brake pads and possibly even the brake caliper.

If you take the wheel off, warped rotors will look pitted and rough. You might even notice little cracks on the rotors, which will make the jerking vibration worse when braking.

3. A Failing Master Cylinder

A bad master cylinder with a single failed piston cup inside can cause uneven braking, which can feel like jerking or roughness inside the car. This is especially true for tandem, split diagonal master cylinders where one of the piston cups applies the brakes on the front left and the rear right wheel or vice versa.

When one of the piston cups fails, but the other still works, two brakes on opposite corners of the car brake while the other two continue moving. This causes an imbalance with the braking force, which can cause hard vibrations as you slow down.

The even larger concern here is that once one piston cup fails, the other is likely about to go, which would leave you without any brakes.

If it is a bad master cylinder, you’ll likely notice the brake pedal feeling spongy, and it might even fade to the floor. If the problem is causing a leak in the hydraulic brake fluid, the brake fluid level sensor will likely detect it, and the red brake warning light will appear in the dash display.

4. A Stuck Brake Caliper

If your car jerks when slowing down and pulls to one side, it’s most likely a stuck or sticky brake caliper. Rust in the brake caliper, on the pistons or the slide pins, or poor lubrication can cause a single caliper to clench down hard on the rotor. If it’s a front caliper problem, you might also notice a vibration in the steering wheel.

When you take your foot off the pedal, the caliper might not release or will only release partially. This will cause the car to feel like it’s still pulling to one side, as if it’s mimicking a bad front alignment issue. However, you’ll likely also hear metallic rasping and grinding noises as well.

You might be able to get the brake caliper to release by tapping it with a hammer and lubricating the caliper pistons and slide pins. Even if it works, this is a short-term fix at best, and you’ll most likely need to replace both calipers on that axle.

5. Bad Suspension & Worn-Out Shocks

If your car bounces, the front end dips, or it seems to jolt when you rapidly decelerate, it could be that you have a failure in your suspension system’s bushings, or both shocks on an axle are worn out. If this is the case, you’ll also feel a similar bounciness when you drive over a speed bump or railroad tracks.

Most cars with bad shocks also tend to have a lot of body roll when cornering. You might even get a warning light on the dash with an error message for a chassis control system failure or a problem with the electronic stability control malfunction. This is basically the car saying that it can’t manage the body roll and handling caused by the bad suspension system components.

6. Low or Degraded Transmission Fluid

If your car has been making hard gear changes when downshifting and you notice it starting to jerk when you slow down, you might have low transmission fluid or badly degraded transmission fluid. Your car’s transmission relies on the fluid to lubricate the system and make smooth gear changes.

If you’ve recently overheated your transmission with a lot of long, heavy towing, the fluid might have oxidized and degraded. This is somewhat common in light-duty pickup trucks that don’t have a transmission radiator or transmission cooling system that are asked to tow large boats, campers, and equipment trailers.

As the transmission temperature climbs over 175 to 220 degrees or more, the lubricating properties of the transmission fluid break down, making future gear changes clunky. Then when you step on the brake pedal the torque converter and the TCM struggle to get the transmission to change down smoothly, causing the car to jerk or shudder.

If degraded, oxidized transmission fluid is the reason your car is jerking when you slow down, the fluid will look dark and might even have little metallic flecks in it. You’ll likely notice a whining noise right before the transmission shifts. It might also slip out of gear, or you’ll seem to lose a gear like the reverse.

If you hook the car up to a code reader, it might throw a code P0218 Transmission Over Temperature. This is a strong sign that you have bad/degraded transmission fluid.

If you leak in your transmission seal, other issues that cause a low fluid level will have the same poor lubrication effect. If your car or truck has an oil level sensor, it might throw a warning light to let you know you have low fluid. You might even notice transmission fluid spots under the car.

7. A Bad Torque Converter

If your car has an automatic transmission and the torque converter is going out or was damaged by bad/low transmission fluid, it can struggle to shear the power of the transmission or fail to activate the automatic clutch when braking. This can sometimes cause violent jerking and shuddering as it fails to downshift properly with the power of the engine.

The most common symptoms of a bad torque converter often start as problems shifting up or down, with rough gear changes. The transmission can also be prone to slipping out of gears. If you drive with a bad torque converter long enough, the transmission won’t shift, and it will run very hot.

If you get a check engine light, a bad torque converter will throw a code P0740 for Torque Converter Clutch Circuit Malfunction.

8. A Bad TCM or Transmission Valve Body Problem

If the TCM or the components inside the transmission valve body are compromised, it can cause problems with the way the torque converter downshifts, resulting in shuddering, jolting, or jerking when braking. The transmission valve body is essentially the brain of an automatic transmission and is usually integrated with the TCM.

If you have a problem with the TCM or one of the components inside the transmission valve body, you’ll also notice the car struggling to shift smoothly into high gear or getting stuck in gear. It might also cause the transmission to shift unpredictably or be sluggish starting out. You might also notice the check engine light flashing when the transmission struggles to change gears; then, it goes off again.

If you do get a check engine light, you can hook it up to a simple code reader. If the TCM or some part of the valve body is bad, you might get one of the following codes.

9. A Bad MAF Sensor

A problem with the Mass Air Flow (MAF) sensor can easily cause an imbalance in the fuel/air mixture, causing the engine to sputter and jerk when slowing down. Usually, the jerking is more pronounced if the engine goes from running at high RPMs, like when you’re driving at highway speed, and then slows down quickly, such as pulling off the highway at a short exit ramp.

When a MAF sensor is going bad, you’ll also notice other symptoms such as dark exhaust, rough starting, and a hard idle when you’re sitting at a stop. A bad MAF sensor will eventually cause the check engine light to come on and throw a code.

Sometimes cleaning the sensor with a MAF sensor cleaner is all you need to get it running correctly again. Though you can also replace the sensor for a cost of $150 or so. Though a lot of times when a MAF sensor goes bad, there’s usually something else in the air system that starts the problem!

10. A Dirty or Stuck Throttle Body

A dirty throttle body can stick or fail to respond in time to the engine’s fuel system, which imbalances the fuel/air mixture causing the engine to shudder or jerk when the RPMs change. A lot of times, a dirty throttle body is caused by a process known as “co*king” where deposits build up along the butterfly valve. If you have a bad habit of running on a dirty air filter, it can also cause the throttle body to stick.

A dirty throttle body that starts sticking when you accelerate will also leave the engine feeling down on power. You’ll probably also notice your MPG taking a nosedive. Eventually, the fuel/air mixture imbalance will cause the ECU to throw a check engine light.

If you open up the air intake manifold, you’ll usually find black deposits around the throttle body and its butterfly valve.

11. A Bad Ignition Coil

An ignition coil that causes the engine to misfire can feel like jerking or shuddering as the ECM attempts to compensate. When a coil stops sending a spark or sends only an intermittent spark the spark plug doesn’t fire on time. It can also cause misfires as unburned fuel lingers in the combustion chamber.

A bad ignition coil will also affect the fuel economy, and the car will be hard to start, prone to stalling. You’ll also notice a had idle, which can be very ugly if you have more than one coil going out. Usually, an ignition coil will activate the check engine light, and the ECM will throw a code.

If you have a multimeter or voltmeter, you can hook it up to the suspect ignition coil. If it gives you a reading of zero Ohms, then you’ll have confirmation that it was a bad ignition coil causing your car to jerk when slowing down.

Once an ignition coil starts to go bad, it needs to be replaced. However, you shouldn’t be surprised if you also need to replace the spark plug with it. If your car has around 75,000 miles or more, chances are good that more coils are going to fail soon. So, it might be a good idea to just have all the ignition coils and plugs replaced as part of a tune-up. This might seem like it costs you more in the short term, but it will actually save you a fair amount of money in the long term.

12. Bad Fuel Injectors

One or more bad fuel injectors that alter the fuel/air balance can cause the engine to idle hard and jerk when decelerating. This is usually because the fuel injector’s internal solenoid is stuck fully open or closed. The ECU can’t adjust the fuel side of the internal combustion process, causing misfires and timing problems. You’ll likely also notice poor MPG and strange fuel odors in the exhaust.

Given enough time, a bad fuel injector will usually start to cause misfires. This will then cause the check engine light to come on; when it does, you can check the ECM with a code reader.

13. A Clogged Fuel Filter or Bad Fuel Pump

If your car’s fuel filter is clogged or the fuel pump is going out, the engine’s fuel rail won’t be able to respond to the ECM’s changes in the fuel/air mixture, causing the engine to feel down on power and jerk when slowing down. You’ll likely also notice the engine is hard starting and has a rough idle. A buzzing or electric humming noise by the fuel tank is also a telling sign that the fuel pump is bad.

If you’ve gone more than 30,000 or 40,000 miles since your last fuel filter replacement, then there’s a strong chance that the clogged filter is at least one factor contributing to your engine problems. Though a badly clogged fuel filter can also stress out the fuel pump causing it to go fail as well.

If you replace the clogged fuel filter and the car stops jerking when you slow down, then you got away with one. If the problem persists after you replace the fuel filter and you hear buzzing noise by the fuel tank, then you likely need a mechanic to replace the bad fuel pump as well.

You can check the ECM for a specific error code if you get a check engine light.

Code P0230 is a generic code for a problem with the fuel delivery system.

14. A Vacuum Leak

A vacuum leak can allow unmetered air into the combustion chamber, which affects engine performance resulting in hard starts, rough idles, and the engine shuddering when you decelerate. You might also notice that the engine has been hesitating when you step on the gas and idles rough.

If you listen in the engine bay when the car is running, you might also hear a strange hissing or wheezing noise as the unmetered air passes through a slit or crack in a hose. You can try a propane enrichment test if you’re having trouble spotting the exact leak.

Eventually, the engine performance problems caused by a vacuum leak will cause the ECM to turn the check engine light on. This will throw a code that you can read on an OBD II

A code P0171 or P0174 indicates a lean condition from too much-unmetered air in the fuel/air mixture. However, this could also be other faults in the air system or the air intake manifold. This is where the propane enrichment test comes in handy!

Frequently Asked Questions

Is It Safe to Drive a Car That Jerks When Decelerating?

While you might be able to drive around with slightly warped rotors or bad shocks for a while, most of the things that cause a car to jerk when slowing down are symptoms of a much more serious fault. Driving around with a car that can’t decelerate smoothly can damage the transmission, leave you stranded with a stalled car, or cause serious engine damage. So, the smart thing is to park the car until you can diagnose the problem or get it to a mechanic.

How Can I Know For Sure If I Have a Brake System Problem?

If you don’t trust yourself to diagnose a brake system problem, then the wisest thing to do is to take the car in for a brake inspection. Anywhere that offers tire rotations typically also offers brake inspections.

This will let you know if a brake caliper, warped rotors, or another brake system problem cause the reason your car is jerking when it slows down. These shops also have code readers that can let you know about any other engine faults, and they can usually change your fuel filter as part of a comprehensive oil change.

Putting the Brakes on Jerking

Anytime your car starts jerking when you’re slowing down is a serious cause for concern. Even minor issues like bad suspension components or mildly warped rotors can be serious safety issues.

Let alone the risk of more major faults, such as a TCM issue or bad/low transmission fluid, which can damage your transmission. Catching these transmission problems early will go a long way toward preventing serious transmission damage later.

Engine and fuel system problems are also common reasons why a car might start jerking or jolting when you decelerate. Dramatic changes in RPMs can expose mechanical faults that cause an imbalance in the fuel/air ratio. This includes things like vacuum leaks and a sticky throttle body with a MAP sensor problem that causes the engine to run overly lean as RPMs decrease with braking.

Though something as simple as a clogged fuel filter can cause problems with the fuel pump or even allow debris to get to the fuel rail. This can then cause a fuel injector to get stuck open or closed, further fouling the fuel/air ratio when braking.

Written By

Jason Farrell

Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.