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Alternator
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2019 - 2021 BMW Z4 High-Output Alternator (OEM)

Only 1 left in stock
$159.95

ℹ️ Product Notes

This is a used part. This Alternator assembly is rated for 180 amps.

Fits 180A systems without 48V mild hybrid technology. Check your old part for the 180A rating. Does not fit vehicles with the 48V starter-generator system.
Condition: Excellent (A)
Like new, minimal to no wear
38,780 miles
Odometer reading when part was removed
See Other BMW Z4 Alternators
SKU #
8121925-81101-106

Why Buy Used OEM Parts?

✓ Quality-Verified: Every used OEM part we sell has been professionally inspected and tested to ensure it meets our quality standards. While it may show some cosmetic wear from previous use, it's fully functional and ready to install.

✓ Original Equipment: This is a genuine OEM (Original Equipment Manufacturer) part - the exact same part that came with your vehicle from the factory. It's designed specifically for your make and model, ensuring perfect fitment and performance.

✓ Works Like New: Despite some visual wear, this part will perform just as well as a brand new one. The internal components and functionality are intact, giving you the same reliability you'd expect from OEM quality.

✓ Significant Savings: Save 50-80% compared to buying new! Used OEM parts offer exceptional value - you get factory quality at a fraction of the cost. It's the smart choice for budget-conscious vehicle owners who won't compromise on quality.

✓ Risk-Free Purchase: We stand behind our used parts with a generous 6-month warranty, 30-day returns, and 100% money-back guarantee. If it doesn't work out for any reason, simply return it for a full refund. You have nothing to lose!

🛡️ 30-Day Returns + 6-Month Warranty - Buy with Confidence!

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Vehicle Fitment Guide

This part fits the following vehicles:

BMW
Z4 2019-2021 (tapclick to expand)(tapclick to hide)
Swipe left/right to see more info
SubmodelSUB-
MODEL		 Body Style Years Engine Attributes
M40i Convertible 2019 - 2021 L6 3.0L Turbo RWD | Automatic
sDrive20i M Sport Convertible 2019 - 2020 L4 2.0L Turbo RWD | Automatic
sDrive20i Sport Line Convertible 2019 - 2020 L4 2.0L Turbo RWD | Automatic
sDrive30i Convertible 2019 - 2021 L4 2.0L Turbo RWD | Automatic
M40i First Edition Convertible 2020 - 2021 L6 3.0L Turbo RWD | Automatic
sDrive M40i Convertible 2020 - 2021 L6 3.0L Turbo RWD | Automatic
sDrive20i Convertible 2021 L4 2.0L Turbo RWD | Automatic

⚠️ Important: Please verify your vehicle's year, make, model, and specifications before ordering. If you're unsure about fitment, contact our customer service team for assistance.

Policies

Shipping & Handling

  • Standard shipping: 3-7 business days via UPS Ground
  • Parts are carefully packaged to prevent damage during transit

Returns (30 Days)

We accept returns within 30 days of delivery for this part.

  • Defective parts: We will replace the part or issue a refund at our discretion
  • Electronic parts: Must be returned with the sealed inspection bag unopened. The clear bag allows full visual inspection before opening. Once opened, electronic parts can only be exchanged for a replacement if defective — no refunds
  • Programming: "Needs to be programmed to my vehicle" is not a valid return reason. Many modules require dealer programming — we're happy to help connect you with resources if your dealer says it's not programmable
  • Return shipping: We cover return shipping as part of our 100% money-back guarantee
  • Parts must be returned in original packaging and unmodified condition
  • Poorly packaged returns that arrive damaged will not be credited

6-Month Warranty

All used parts include a 6-month warranty from the date of purchase.

  • If your part fails within 6 months, we will send a replacement
  • Refunds are only issued if we cannot provide a suitable replacement
  • Warranty covers defects — not installation errors, misuse, or damage after installation

Note: Warranty is for replacement, not refund. A part failing on day 80? We'll replace it. But the return window for refunds is 30 days.

Damaged in Shipping?

If your part arrives damaged:

  • Stop immediately — do not install the part
  • Keep all original packaging and boxes
  • Take clear photos of the damage and packaging
  • Contact us within 48 hours of delivery

We will handle the carrier claim. You are not responsible for shipping damage — we just need your help documenting it.

Order Cancellation

Orders can be cancelled before shipment for a full refund. Once shipped, cancellations follow our return policy.

Symptoms & Diagnosis

Warning Signs of a Failing High-Output Alternator

  • Dimming headlights, especially at idle
  • Battery warning light on the dashboard
  • Slow or no-start condition
  • Unusual noises, such as whining or grinding, coming from the alternator area
  • Electrical issues like malfunctioning power windows or radio

Testing the Alternator

To determine if the alternator is the problem, you can perform a few simple tests:

  1. Voltage Test: Use a multimeter to check the voltage at the battery terminals while the engine is running. A healthy alternator should produce around 13.5 to 14.5 volts. Lower voltage indicates a potential alternator issue.
  2. Load Test: Have a professional perform a load test on the alternator. This test simulates the electrical demands of the vehicle and assesses the alternator's ability to maintain voltage under load.
  3. Visual Inspection: Check the alternator for any visible damage, such as cracked housings, loose wiring, or corrosion.

Common Failure Causes

  • Overheating due to engine heat or restricted airflow
  • Worn brushes or slip rings
  • Faulty voltage regulator
  • Damaged bearings
  • Electrical shorts or surges

Buyer's Checklist

What to Look For When Buying

  • Compatibility: Ensure the alternator is designed for your vehicle's year, make, and model.
  • Amperage Output: Verify the alternator's amperage output matches or exceeds the original equipment specifications.
  • Warranty: Check for a warranty that covers defects in materials and workmanship.

Quality Indicators

  • Reputable Brand: Choose alternators from well-known and trusted manufacturers.
  • Quality Components: Look for alternators with high-quality internal components, such as bearings and regulators.
  • Testing and Inspection: Ensure the alternator has been thoroughly tested and inspected to meet performance standards.

What's Typically Included

  • The alternator itself
  • Mounting hardware (sometimes)
  • Installation instructions (sometimes)

Installation Overview

Difficulty Level and Estimated Time

Replacing an alternator is generally considered a moderate DIY project. Estimated time: 2-4 hours.

Special Tools Needed

  • Socket set
  • Wrench set
  • Multimeter
  • Belt tensioner tool (may be required)

Critical Steps and Tips

  1. Disconnect the Battery: Always disconnect the negative battery cable before starting any electrical work.
  2. Locate the Alternator: Identify the alternator and its mounting bolts.
  3. Remove the Belt: Use a belt tensioner tool to release tension on the serpentine belt and remove it from the alternator pulley.
  4. Disconnect Wiring: Disconnect the electrical connectors from the alternator.
  5. Remove the Alternator: Unbolt the alternator from its mounting bracket and carefully remove it.
  6. Install the New Alternator: Install the new alternator in the reverse order of removal.
  7. Reconnect the Battery: Reconnect the negative battery cable.

DIY or Professional Installation?

While replacing an alternator can be a DIY project, professional installation is recommended if you are not comfortable working with electrical systems or if you lack the necessary tools. A professional can ensure the alternator is properly installed and that the electrical system is functioning correctly.

Buying Options

Here's a comparison of the available options:

FeatureUsed OEMRefurbished OEMNew Aftermarket
PriceLowestMid-RangeMid-Range to High
ConditionUsed, tested and inspectedProfessionally restored with new componentsBrand New
QualityGenuine factory partGenuine factory part, restoredBuilt to OE specifications
ReliabilityGood, depending on prior usageGood, with new or reconditioned componentsCan vary depending on the manufacturer
WarrantyTypically limitedTypically longer than used, shorter than newTypically longer than used OEM and Refurbished OEM

Used OEM

Used OEM alternators offer the best value. These are genuine factory parts that have been tested and inspected to ensure they are in good working condition. They are available at significantly lower prices than new alternators.

Refurbished OEM

Refurbished OEM alternators are factory parts that have been professionally restored with new components. This option provides a balance of price and reliability.

New Aftermarket

New aftermarket alternators are brand new third-party parts built to OE specifications. These can be a good option if you prefer a new part and are willing to pay a bit more.

Typical Lifespan

A high-output alternator typically lasts between 5 to 10 years or 80,000 to 150,000 miles.

Factors that affect longevity:

  • Driving conditions (frequent short trips can shorten lifespan)
  • Climate (extreme temperatures can affect performance)
  • Electrical load (high electrical demands can strain the alternator)
  • Maintenance (regular inspections can identify potential problems early)

Price Ranges

  • Used OEM: $75 - $150
  • Refurbished OEM: $150 - $250
  • New Aftermarket: $200 - $400

Labor costs for installation typically range from $100 to $300, depending on the mechanic's hourly rate and the complexity of the job.

Total job cost estimates:

  • Used OEM: $175 - $450
  • Refurbished OEM: $250 - $550
  • New Aftermarket: $300 - $700

Vehicle-Specific Notes

Some 2017-2024 BMW and Toyota models have known issues with the electrical system, including voltage fluctuations and premature alternator failure. Check for any Technical Service Bulletins (TSBs) related to the alternator or charging system for your specific vehicle model. Some owners have reported issues with the voltage regulator causing overcharging.

Verification After Install

After installing the new alternator, verify proper operation by:

  • Checking the Battery Voltage: Use a multimeter to check the battery voltage with the engine running. It should be between 13.5 and 14.5 volts.
  • Listening for Unusual Noises: Listen for any unusual noises, such as whining or grinding, coming from the alternator.
  • Observing the Battery Warning Light: Ensure the battery warning light on the dashboard is off.
  • Testing Electrical Components: Test various electrical components, such as headlights, power windows, and radio, to ensure they are functioning correctly.

FAQ

Q: How do I know if my alternator is bad or if it's just my battery?
A: A simple test is to jump-start your car. If it starts and runs fine, but dies shortly after removing the jumper cables, it's likely the alternator. If it doesn't start at all, it could be the battery. Have both tested to be sure.

Q: Can I drive with a bad alternator?
A: It's not recommended. A bad alternator can cause your car to stall, leaving you stranded. It can also damage other electrical components.

Q: Will a new high-output alternator fix my dimming headlight problem?
A: If the dimming headlights are caused by a weak alternator, then yes, a new high-output alternator should fix the problem. However, dimming headlights can also be caused by other issues, such as poor wiring or a weak battery.

Q: What does "OEM" mean?
A: OEM stands for Original Equipment Manufacturer. It means the part was originally made by the same manufacturer that made the parts for your car when it was new.

Q: How long does it take to install a new alternator?
A: On average, it takes about 2-4 hours to install a new alternator. The time can vary depending on the vehicle model and the mechanic's experience.

Part Specifications

OEM Part Numbers:

  • BMW: 12318634166, 12318634167, 12318654280, 12318689830, 12318689831, 12318689832

Fits Years: 2019 2020 2021

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