Bad Vacuum Pump Symptoms, Causes, and Replacement Cost

Internal combustion engines running on unleaded gas generate high pressure within the enclosed crankcase. This pressure serves to operate various pulleys and belts, such as those driving alternators and AC units. To prevent excessive pressure buildup, these engines utilize a vacuum pump for its release. A bad vacuum pump produces different symptoms.

Diesel engines rely on vacuum pumps to run other systems, notably the brake system and often the air conditioning system. Consequently, when a brake vacuum pump goes bad, it badly affects the performance of the braking system. For instance, the distinct rattling noise produced by a bad car engine pump serves as an indicator that you need to repair or replace it. This article explains the bad vacuum pump symptoms, causes, and replacement cost.

What Is the Vacuum Pump?

A vacuum pump is a mechanical device designed to create a state of vacuum by removing atmospheric pressure from a closed area.

Vacuum Pump

In nature, vacuums are naturally filled by atmospheric pressure seeking equilibrium. This principle is evident in the dynamics of airplane flight, where the design of the wings and airflow dynamics create a pressure differential that allows airplanes to stay airborne.

Initially, a brake vacuum pump was most commonly used in diesel engines primarily to power brakes and facilitate the movement of climate control doors within the dashboard. This was necessary because diesel engines do not generate vacuum on their own.

In vehicles equipped with power-assisted brakes, such as hydraulic brake boosters, a vacuum pump is used to create vacuum pressure.

The vacuum pump draws air out of the brake booster, creating a vacuum that assists in the application of force to the brake pedal. This vacuum pressure amplifies the force applied by the driver, making it easier to engage the brakes and providing power-assisted braking.

Symptoms of a bad Vacuum Pump

When the brake vacuum pump goes bad, it produces the following symptoms:

  • Hissing Noises 
  • Oil Leakage under the Engine
  • Air Conditioner is not Working
  • Poor Fuel Efficiency
  • Hard Brake Pedal
  • Engine Misfires or Rough Idle

1) Hissing Noises 

A malfunctioning vacuum pump can cause significant problems for your car. When there is a vacuum leak, the pressure difference is altered, affecting the vacuum generated by the pump. Luckily, you may detect this issue by listening for a distinct hissing noise, which indicates air leakage from a leak.

Hissing Noise, symptoms of bad vacuum pump

It’s important to note that a vacuum leak doesn’t always stem from a faulty vacuum pump. If the hoses connecting the pump to other components are damaged or loose, they may also produce similar sounds.

2) Oil Leakage under the Engine 

Typically, maximum vacuum pumps are installed on either the right or left side of the engine, usually in close proximity to the brake master cylinder in a diesel vehicle.

Oil Leakage under the Engine

The vacuum pump of your vehicle needs a sufficient supply of oil for proper lubrication and to regulate internal temperature. If you observe oil dripping from the right or left side of the engine, it may originate from the vacuum pump.

It’s advisable to have a mechanic inspect this issue, regardless of your assumptions about the source of the oil leak, as neglecting it could result in significant mechanical failures.

3) AC not Working

If the air conditioning (AC) system of your vehicle suddenly stops working, it is one of the clear symptoms of a bad vacuum pump.

Car AC not working

If you recently had your AC unit serviced and encountered an issue, it is advisable to contact the nearest professional technician who can properly inspect the vacuum pump for potential problems.

4) Poor Fuel Efficiency

Vacuum leaks commonly occur due to a bad vacuum pump, faulty connections, or broken vacuum hoses. Sometimes, if you observe carefully, you may detect a distinct “hiss” noise, which indicates a vacuum leak.

Bad Fuel Economy

But a noticeable decrease in fuel efficiency is often the most common sign of a bad vacuum pump. This is because the delayed exhaust of burnt fuel from the combustor leads to reduced efficiency in burning new fuel. Engine performance can also be affected, but the impact may vary depending on the manufacturer and the specific usage of the vacuum pump.

5) Hard Brake Pedal

A malfunctioning vacuum pump can result in a hard brake pedal, particularly in diesel vehicles that utilize a vacuum pump booster to enhance the performance of the braking system. This symptom is often observed in larger diesel semi-trucks and rear-wheel drive trucks with dual-tire configurations.

Brake Pedal, signs of bad brake vacuum pump

As the pump starts to deteriorate, it generates reduced suction, leading to decreased pressure in the brake master cylinders and within the brake lines. Over time, this drop in pressure progresses to the brake pedal.

When the brake system has ample pressure, the pedal feels firm yet responsive. However, when vacuum pressure is less than the required limit, the pedal becomes stiff and challenging to depress, reducing the performance of the braking system.

If you notice this warning symptom, it is crucial to promptly address the issue by having a certified diesel mechanic examine and repair it. Delaying the necessary repairs can jeopardize your safety, so it is best to take action as soon as possible.

6) Engine Misfires or Rough Idle

A vacuum leak caused by a bad vacuum pump may disturb the fuel-air mixture in the engine cylinder, leading to a rough idle or engine misfire.

Engine Misfiring

You may also monitor that your engine runs unevenly, shakes, or struggles to ensure a steady idle speed as the vehicle is at a stop.

Read More: Rough Idle Causes and Symptoms

Causes of a Bad Vacuum Pump

The brake vacuum pump of your car goes bad due to one or more of the below-given causes:

  • Overheating
  • Blown Fuse
  • Clogged Inlet or Outlet

1) Overheating

Diagnosing a faulty vacuum pump caused by overheating can be challenging. Overheating may be caused by different factors, such as poor ventilation, insufficient engine oil, incompatible pump applications, or a faulty motor. Consistent overheating is a potential indicator of a malfunction.

When testing an overheating pump, start by examining the ventilation passages. If these passages are clogged or located too close to other parts, resolving the issue may be as simple as repositioning the pump for better airflow.

Read More: Engine Overheating Symptoms and Causes

2) Blown Fuse

A blown fuse is one of the major causes of a bad vacuum pump. If your pump fails to turn on, it could be due to blown fuses. Begin by checking the pump’s fuses. If you replace the blown fuses and the pump functions without any further problems, the issue is resolved.

However, if a bad fuse persists as a recurring issue, it can indicate an issue with the electrical power or using a voltage that exceeds the pump’s specifications.

3) Clogged Inlet

The vacuum pump of your car may start slowly or experience restricted flow if there is a blockage at the outlet or inlet. If no blockage is present, the pump may have a faulty capacitor or motor.

In such cases, improper application, particularly the presence of an inlet vacuum or excessive pressure at the outlet, needs to be fixed. Vacuum pump failure in these circumstances can lead to overheating and burning out of fuses, eventually causing failure to the motor or capacitor.

How do you test a Vacuum Brake Pump?

To diagnose an issue with your vehicle’s vacuum pump, check your vacuum supply hose leading to the brake booster for damage, cracks, or kinks. Additionally, uses a vacuum gauge to inspect the engine vacuum at idle.
To test the functionality of your vehicle’s brake booster once the reserve is reduced, apply medium pressure on the brake pedal and restart your engine. If the booster is working efficiently, your vehicle’s brake pedal should drop slightly in response.

FAQ Section

What does a Vacuum Pump do in a car?

The role of the vacuum pump varies depending on the type of IC engine powering the vehicle. In petrol engine vehicles that use unleaded fuel, the vacuum pump is responsible for releasing pressure from the crankcase, which in turn drives various pulleys and belts connected to components such as the alternator and AC system. In diesel engines, the pump is used to run the brake booster, AC system, and other related systems.

How much does a replacement Vacuum Pump Cost?

The replacement cost of a brake vacuum pump depends on the labor cost and the vehicle make and model. The average replacement cost of the vacuum pump is between $30 and $320.

What happens when the brake vacuum pump fails?

The brake booster vacuum pump plays a crucial role in supplying the necessary vacuum for the braking system to function effectively. If the pump goes bad or experiences an issue, your car will lose the assistance provided by the power brake booster. This results in a stiff brake pedal that requires significantly more effort to bring the car to a stop.

Can I drive with a bad brake vacuum pump?

Driving with a faulty brake vacuum pump is not recommended. The vacuum pump plays a critical role in ensuring the proper functioning of essential systems in your vehicle, including the braking system. Additionally, a malfunctioning pump may disturb the functionality of the vital systems, such as the defroster, heating, and air conditioning systems, and may lead to an expensive repair.

What happens if a vacuum is blocked?

When a clog occurs in the vacuum system, it impairs suction and prevents the vacuum from operating effectively. The clog may be located in the vacuum hose, head, or at the junction where the hose connects to the actual vacuum unit.

Can a faulty vacuum pump cause a misfire?

Vacuum leaks, particularly those confined to a specific cylinder, can lead to uneven engine idling and potential misfires. This occurs because the vacuum leak permits more air to enter the affected cylinder and affects its air-fuel mixture, causing a misfire.

Read More

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