2014-2020 BMW i3 Brake Vacuum Pump: Hard Pedal, Diagnosis, and Replacement
A hard brake pedal in your BMW i3 is a serious safety issue, often caused by a failing electric vacuum pump—here’s how to diagnose and fix it.
- A failing vacuum pump causes a hard brake pedal, which is a critical safety failure that dramatically increases stopping distance.
- This pump is essential because the i3 is an electric vehicle and does not have engine vacuum to assist the brakes.
- Before buying a replacement, confirm the part number is 34336857405, which is the updated version for all 2014-2020 i3 models.
- A pump that runs constantly or a brake pedal that is hard only on startup are key diagnostic clues pointing to a vacuum system problem.
Symptoms of a Failing Vacuum Pump
A failing brake vacuum pump is a critical safety issue. The most common sign is a sudden change in how your brake pedal feels. Because the i3 relies heavily on regenerative braking, you may not notice a problem with the conventional brake system until you need it in an emergency.
- Hard Brake Pedal: This is the most significant and dangerous symptom. The pedal will feel unusually stiff and require significantly more leg strength to press down. Some drivers describe it as feeling like the brakes are gone, even though the mechanical brakes still work with enough force.
- Brake System Warning Lights: You may see a general brake warning light, or a combination of ABS and traction control lights on your dashboard. One relevant technical service bulletin notes a "Press pedal harder for usual braking power" message (Check Control message ID24).
- Abnormal Pump Noises: The vacuum pump is designed to run briefly to build pressure and then shut off. If you hear a constant buzzing or humming from the front of the car, the pump may be running continuously trying to overcome a leak. Grinding or knocking sounds can indicate internal failure.
- Hard Pedal on Startup: If the brake pedal is very hard when you first get in the car after it has been parked for a few hours, but softens after the car is on, it may indicate a slow leak in the vacuum system. The pump is losing its stored vacuum over time.
Warning: A hard brake pedal indicates a loss of power brake assist. Your stopping distance will be much longer than normal. Do not drive the vehicle if you experience this symptom.
Known Issues, Recalls, and Technical Service Bulletins (TSBs)
While there are no widespread recalls specifically for the vacuum pump on the 2014-2020 BMW i3 in the US market, the brake system is the subject of some service bulletins.
- TSB B340719: This bulletin addresses a Check Control message (ID24) that reads "CCM Brake system: Press pedal harder for usual braking power." It notes that this fault usually occurs at very low temperatures or in rainy regions. This directly relates to the symptoms of a failing vacuum pump or a leak in the system.
- TSB B610920: This bulletin mentions that multiple check control messages for the brake, suspension, and airbag systems can appear simultaneously. While not specific to the pump, a failing brake component can sometimes trigger a cascade of system warnings.
No recalls were found specifically for the vacuum pump on the 2014-2020 BMW i3. Other BMW models have had recalls for vacuum pumps, but these do not apply to the i3.
Buying a Used 2014-2020 BMW i3 Vacuum Pump
A used OEM vacuum pump can be a cost-effective and reliable alternative to a new part, especially since aftermarket options are not common for this component. Here’s what to look for.
1. Verify Compatibility
The most important step is to match the part number. The primary part number for this pump is 34-33-6-857-405. This number supersedes the older part number, 34-33-6-789-279. Always confirm the number on your existing pump before purchasing a replacement. The pump is used across all i3 and i3s models from 2014 to 2020.
2. Physical Inspection
When inspecting a used pump, check for the following:
- Cracks or Damage: Examine the black plastic housing for any cracks, especially around the mounting points and hose connections.
- Connector Pins: Look inside the electrical connector. The pins should be straight, clean, and free of corrosion.
- Vacuum Ports: Ensure the inlet and outlet ports are clean, undamaged, and free of debris.
- Signs of Contamination: The pump should be dry. Any signs of oil or other fluids inside the vacuum ports could indicate problems with other vehicle systems.
3. Source and Warranty
Purchase from a reputable auto recycler that offers a warranty. A 30-day or longer warranty provides protection in case the part is defective. Reputable sellers will provide photos of the actual part you are buying, not a stock photo, and often include the mileage of the donor vehicle.
Pro Tip: A used pump from a lower-mileage vehicle is generally preferable. However, a pump from a car used primarily for highway driving may have fewer brake applications (and thus, fewer pump cycles) than a city-driven car with the same mileage.
Replacement Overview
Replacing the vacuum pump on a BMW i3 is a moderately difficult job that a skilled DIY mechanic can perform. Accessing the pump is the main challenge.
- Location: The pump is located in the front driver's side wheel well area, behind the fender liner.
- Difficulty: 3 out of 5.
- Estimated Time: 1.5 - 2.5 hours.
- General Steps:
- Safely jack up the front driver's side of the vehicle and remove the wheel.
- Remove the plastic fender liner to expose the components in the wheel well.
- The headlamp assembly may need to be removed for better access.
- Locate the vacuum pump. It is held in place by two mounting bolts.
- Disconnect the electrical connector and the two vacuum hoses. The main vacuum line has a pinch-style connector.
- Unbolt and remove the old pump.
- Installation is the reverse of removal. After installing the new pump, turn the car on and press the brake pedal several times. You should hear the new pump run briefly and then stop. The brake pedal should feel firm and responsive.
| Part Type | Estimated Cost |
|---|---|
| New OEM | $530 - $640 |
| Used OEM | $75 - $150 |
| New Aftermarket | Not readily available |
| Shop Labor | $225 - $440 (1.5-2.5 hours at $150-$175/hr) |
Frequently Asked Questions
Why does my electric car need a vacuum pump?
Conventional gasoline engines create a natural vacuum in the intake manifold, which is used to power the brake booster. Since electric cars like the i3 don't have a gasoline engine running all the time, they need a separate electric pump to create that vacuum for brake assist.
Can I drive my i3 with a bad vacuum pump?
No. While the brakes will still function mechanically, the loss of power assist makes the pedal extremely hard to press and dramatically increases your stopping distance. It is unsafe to drive a vehicle with a known brake assist failure.
Is the brake vacuum pump the same as the ABS pump?
No. The vacuum pump creates suction for the brake booster to provide power assist for normal braking. The ABS pump (or module) is a separate hydraulic unit that rapidly pulses the brakes to prevent wheel lock-up during a hard stop.
Do I need to bleed the brakes after replacing the vacuum pump?
No. The vacuum pump is part of the air-side of the brake booster system. Replacing it does not open the hydraulic brake lines, so bleeding the brakes is not required for this specific job.
Technical Specifications
OEM Part Numbers: 34-33-6-857-405 34336857405 6857405 34-33-6-789-279 34336789279 6789279
Electric vacuum pump for brake booster system.
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- BMW i3: