I presume you have noticed that your vehicle’s RPM meter gives random readings. Do not stress over it as I will talk regarding this issue in this article. Well, RPM or revolutions per minute measures how fast a car’s engine is operating at a given time. It can affect a car’s performance, particularly acceleration, power, fuel efficiency, and gear shifting.
So, why does my RPM go up when I brake? Before answering it, I want to add something. When you brake, the automatic transmission tries to adjust for the change in speed. It can cause your car’s RPM to increase (1). But if it is unusually high, then you must think about it.
In short, the most common reason for the unusual RPM increase is issues with vacuum power-assisted brakes. It may also indicate other issues like a leak in the brake booster, a failing torque converter in automatic cars, or problems with the idle air control valve (2,3,4). Like these, you can learn more about the reasons throughout this article.
Car Braking System, RPM, & Their Relationship
Please take a minute to read this part, as it will give you the basics of car brakes and their connection with RPM.
Definition of RPM
As I said, RPM defines the speed of a car. More precisely, we can measure how many times a piston goes up and down in our vehicles. It may also refer to the times the engine spins (5, 6, 7). The faster the RPM, the more power is generated.
RPM greatly influences the fuel consumption in your car. If the RPMs are too high, they can use more fuel and wear down the engine faster (8, 9, 10). Alternatively, a lower RPM outcome less fuel consumption in a vehicle. It is suitable for more economical driving (11,12).
RPM also provides crucial information for gear shifting. It ensures smooth acceleration and prevents engine strain or damage (13).
Definition of Brake System
Well, the braking system in a car works by converting kinetic energy into heat energy through friction (14). Pressing the brake pedal pushes a rod that, in turn, pushes the master cylinder piston. This action sends pressurized brake fluid to the brake caliper. It causes the pistons to press against a steel rotor disc, creating friction to slow the spinning of the wheels ((15, 16).
You can find rotors attached to each wheel hub. Hence, the brake pads get pressed into these rotors. As the pads press into the rotors, the wheels slow down until the vehicle comes to a stop. Then again, brake lines connect the master cylinder to the vehicle’s brake calipers. They provide passageways through which the brake fluid flows (17).
RPM and Braking Relationship
You may be fascinated by knowing the interconnection between RPM and braking systems. Hence, engine torque is related to engine speed or RPM. It plays a crucial role in the performance and functionality of brake systems.
High torque levels put more stress on the brake system. It forces the system to work harder to slow down or stop the vehicle (18). In regenerative braking systems, RPM also impacts the overall efficiency and effectiveness of the braking process.
Usually, when we accelerate or decelerate our car, we may notice the RPM increase or decrease. If you accelerate, the engine exerts more power and increases the power and RPM. Similarly, when you brake, the car slows down to a stop. In this scenario, automatic transmission is essential. It tries to adjust the change in speed. When it starts working, you can see rise of RPM on the meter. And it is expected to experience.
Why Does My RPM Go Up When I Brake?
Now, I will explain the reasons for the sudden increase of RPN during brakes. I hope you will identify the particular causes and solve them soon.
Faulty Idle Control Valve
The increase in RPM during braking in automatic transmission vehicles can be due to several reasons. For instance, the idle control valve regulates the engine’s idle speed. But when it becomes faulty, it can cause the engine to rev up higher than normal before the transmission shifts into higher gears (19). In some cases, the engine may stall, significantly when idle, and starting the car may be difficult (20, 21).
Automatic Transmission Issue
If there’s a problem with the automatic transmission, the shifting becomes irregular or delayed. It increases RPM.
Transmission Fluid
For sure, this fluid has a significant impact on the RPM of a car. A leak or extra flow of the transmission fluid can cause irregularity while changing gears or accelerating. As a result, it will affect the RPM (8).
A Slipping Transmission
A slipping transmission means that it can’t shift or engage gears the way it usually would. It can also increase the RPM when you brake (3). Then, a leaking transmission is another common cause of high RPM before shifting. It is because fluid loss will cause the gears to slip. You get rising RPM for this reason too.
Issue with the Throttle
The throttle of a car controls the engine’s speed. It directly impacts the RPM by regulating the air entering the engine (22). However, if this component has defects or malfunctions, it will raise the RPM during braking.
Vacuum Leaks
Vacuum leaks in a car engine can lead to unusually high RPMs. Well, the engine is susceptible to calculating the air entering it for the right air-fuel mixture (23, 24). Some symptoms of a vacuum leak are rough idle, slow acceleration, misfires, backfires, and a high pitch noise from the engine (25). The check engine light may come on because of a vacuum leak.
Impact of Increased RPM on Vehicle Performance
It’s not like that you get high RPM and reach your destination faster than usual. It definitely has some impacts on acceleration and speed of your car.
The first impact would be the increased fuel consumption. You may need to pour more fuel as the engine works harder to maintain the higher RPM. It will also cause another issue – premature wear. Consistently higher RPM can cause tears and wear on the engine and relevant components.
The sudden increase in RPM may also affect your car’s overall performance. You may experience difficulties while driving. For example, the car may not respond as expected when accelerating or decelerating. It will make your driving risky and uncomfortable.
How to Troubleshoot High RPM During Braking
So, you can see unusual revolutions per minute (RPM) have an odd impact on your driving. Let’s focus on how you can avoid the problem. Thus, you must ensure that the rising RPM is normal. I have already talked about it. If not, you may start troubleshooting.
If your car has a leaking transmission, you must solve it soon. Repair the leaks and fill the right fluid for the transmission.
If you suspect throttle-related issues, consider the following steps:
- Locate the throttle body and check for any visible signs of damage, dirt, or carbon buildup. Then, for the manual, you need to calibrate the throttle sensor. Disconnect the negative terminal of the battery to reset the throttle sensor.
- Now, reconnect the battery after a few minutes and start the car. Drive the car to allow the throttle sensor to recalibrate. You may also use an OBD2 scanner to check if the throttle is fine.
For a defective idle air control valve, you may follow these instructions:
- Locate the valve and inspect if there are any signs of dirt, carbon buildup, or physical damage (like the throttle body).
- Check all the electrical connections to the valve. Securely connect the wiring harness if you find any frayed wires or loose connectors.
- You may try using a multimeter to test the valve’s resistance. Replace the valve if it fails the resistance test.
Follow these steps to fix a vacuum leak:
- Of course, you must locate the vacuum leak first. You can check hoses, gaskets, and connections for signs of wear, cracks, or disconnections. Also, check vacuum hoses for cracks, splits, or deterioration.
- For the leakage test, I suggest you use a smoke machine. Then, introduce smoke into the vacuum system and observe where it escapes. You may repair or replace damaged components accordingly.
Final Words
Why does my RPM go up when I brake? I guess you have understood the reasons well. You can identify the symptoms and follow my instructions to solve the unusual going up of RPM when you press the brake pedal.
You have nothing to do for a normal increase – your car’s automatic transmission will normalize the speed reading automatically. If the readings are consistently high, then follow what you should do. Still, if you cannot figure it out, call a professional mechanic to solve them.
That’s it. Thanks for reading this article.
