2015 BMW i3 REX Complete Maintenance Schedule & Service Guide

Key Takeaways

• The 2015 BMW i3 REX combines an electric motor with a 650cc two-cylinder range extender engine that requires periodic oil and filter changes; the engine has an oil capacity of approximately 2.6 liters .
• Engine oil and filter should be changed approximately every 10,000 miles or 12 months, as determined by BMW's Condition Based Service (CBS) system .
• Brake fluid must be replaced every 2 years due to moisture absorption; the vehicle check/inspection is typically performed at the same interval .
• Spark plugs are officially listed as service items for the REX in some BMW documents, but other BMW documentation states they are "long-term rated" and do not need periodic replacement due to the engine's light-duty operating conditions .
• A Safety Recall (17V-088) affects certain 2014-2017 i3 REX models for inspection and potential replacement of the fuel tank vent line; approximately 19,130 U.S. vehicles are potentially affected .
• The i3 REX uses a cam chain, which should last well beyond the serviceable life of the vehicle given the REX's light duty cycle .

Understanding the 2015 BMW i3 REX

The 2015 BMW i3 with Range Extender (REX) is a unique vehicle that pairs a high-voltage battery and electric motor with a small 650cc two-cylinder engine derived from the BMW C650 scooter . This engine does not drive the wheels; it functions as a generator to recharge the battery, extending the vehicle's range. Because the REX engine operates under light and relatively constant loads, its service requirements differ significantly from conventional gasoline engines.

BMW's Condition Based Service (CBS) system monitors actual vehicle usage—including driving conditions and engine operating hours—to determine maintenance needs. Service reminders are displayed through the vehicle's information center . This system tailors maintenance timing to how the vehicle is actually driven, meaning two identical vehicles may show different service due dates based on their unique usage patterns.

BMW Factory Warranty and Maintenance Program

The 2015 BMW i3 REX was sold with comprehensive factory coverage:

• Basic Warranty: 4 years / 50,000 miles
• Powertrain Warranty: 4 years / 50,000 miles
• Corrosion Perforation Warranty: 12 years / Unlimited miles
• Roadside Assistance: 4 years / Unlimited miles
• Scheduled Maintenance: 3 years / 36,000 miles

BMW Ultimate Care offers 3 years or 36,000 miles of factory-recommended maintenance including engine oil, engine filter, brake fluid, and spark plug changes . This coverage was included for the original owner.

Engine Oil and Filter Change

Factory Schedule

The REX engine requires oil changes at intervals determined by the CBS system, typically around 10,000 miles or 12 months . The engine oil capacity is approximately 2.6 liters for a service fill .

Oil Specification

The REX engine uses 5W-30 or 5W-40 synthetic oil meeting BMW specifications . Always replace the oil filter when changing the oil.

Owner Guidance

Many independent specialists recommend a more frequent oil change interval for the REX engine. Pelican Parts recommends changing synthetic motor oil every 5,000 miles for optimal engine protection . This conservative approach is particularly relevant given the extended periods between REX engine use. Some owners choose to change the oil annually as a precautionary measure .

Oil Change Cost: One owner reported paying approximately $150 for a BMW dealer oil change .

Service Interval Reset

The service indicator can be reset by:

1. Pressing the Start-Stop button (without pressing pedals) to switch on the ignition
2. Holding the trip distance recorder reset button for approximately 10 seconds until the first service item is displayed
3. Selecting the service item to be reset
4. Pressing and holding the button until "Reset successful" appears

Brake Fluid Replacement

BMW requires brake fluid replacement every 2 years for the i3, including the REX variant . The brake fluid must meet DOT4 specification .

Service Cost

A brake fluid flush typically costs approximately $180 at a BMW dealership, or around £100 (approximately $129) for a UK owner .

Owner Guidance

Brake fluid is hygroscopic, absorbing moisture from the air over time, which can cause corrosion within the braking system and degrade brake pedal feel. The 2-year interval is a conservative safety standard to ensure braking system integrity. Some owners report switching to a 3-year schedule using extended-life fluid, but the BMW recommendation remains the safest approach .

Vehicle Check/Inspection

A comprehensive vehicle check is typically performed at the same 2-year interval as the brake fluid replacement . This inspection includes a multi-point check of the vehicle's systems and is part of maintaining the vehicle's service history.

Spark Plugs: A Special Case

The Official Position

There is some ambiguity in BMW's documentation regarding spark plug replacement for the REX engine. Some BMW sources list spark plugs as a service item for the i3+REX . However, BMW's official U.S. maintenance document states: "Due to the light duty and relatively constant operating speeds, the range extender engine's spark plugs and air filter are long-term rated, which do not need periodic replacement" .

Owner Guidance

Given the REX engine's light duty cycle, spark plugs are not expected to wear at the same rate as in a conventional gasoline engine. The engine uses a cam chain, which should last well beyond the serviceable life of the vehicle . Unless the CBS system indicates a need, most owners may not need to address spark plugs during the vehicle's service life.

Engine Air Filter

Similar to spark plugs, BMW's official documentation states the engine air filter is long-term rated and does not need periodic replacement under normal operating conditions .

Cooling System

Coolant Expansion Tank

A Technical Service Bulletin addresses an issue where a leaking coolant expansion tank can trigger a check control message: "DRIVETRAIN: only electric drive possible" . If the coolant expansion tank is damaged, replacement is recommended, and the cooling circuit should be bled and refilled using BMW-approved coolant.

Coolant Specification

The cooling system uses BMW-approved coolant with antifreeze . There is no prescribed change interval for the REX engine coolant.

Service Mode and Maintenance Cycle

Service Mode Activation

Service mode must be activated for certain maintenance procedures. This can be activated manually or using diagnostic tools.

REX Maintenance Cycle

The REX engine automatically performs a self-maintenance cycle if it has not been used for an extended period, typically around 50 days . During this cycle, the REX engine runs for approximately 10-12 minutes to lubricate internal components and ensure proper operation. This maintenance mode will only run if the battery state of charge is below 75% .

Owner Guidance: This is a normal function and does not require user intervention. If ethanol-blended fuel is used in the REX, some owners recommend using a tank of fuel every 90 days or so to prevent fuel degradation .

Important Recalls and Service Actions

Recall 17V-088: Fuel Tank Vent Line

This safety recall affects certain 2014-2017 BMW i3 REX models produced between March 2014 and December 2016 . Approximately 19,130 U.S. vehicles are potentially affected.

Issue: A section of the fuel tank vent line adjacent to the positive battery cable sleeve may wear through over time, potentially causing a fuel vapor leak and increasing fire risk .

Correction: The repair includes inspecting the fuel tank vent line and replacing it if damaged, and attaching a clip between the vent line and B+ cable to prevent contact .

Service Action: Motor Mount Screws (SI B22 01 15)

This Service Action addresses replacement of motor mount screws on i3 and i3 REX models produced from September 2013 to November 2015 . A sudden loss of traction while accelerating sharply may damage the engine mounts.

Note: The REX variant requires replacement of both left and right side mount screws, while the standard i3 only requires the left side .

Summary Maintenance Schedule