2017 BMW i3 REX (94 Amp-hour battery) Complete Maintenance Schedule & Service Guide

Key Takeaways

• The 2017 BMW i3 REX features a 94 Ah (33 kWh) high-voltage battery paired with a 650cc two-cylinder range extender engine. The REX engine requires periodic oil and filter changes, but spark plugs and the engine air filter are "long-term rated" and do not need periodic replacement under normal operating conditions .
• Engine oil and filter should be changed approximately every 10,000 miles or 12 months, as determined by the Condition Based Service (CBS) system; the engine requires approximately 2.6 liters of 5W-30 or 5W-40 synthetic oil .
• Brake fluid must be replaced every 2 years due to moisture absorption, with the vehicle inspection typically performed at the same interval .
• The transmission gear oil is officially classified as "lifetime fill" by BMW, but real-world experience suggests replacement by 95,000 miles with some recommending 30,000-mile intervals .
• A Safety Recall (17V-088) affects certain 2014-2017 i3 REX models for inspection and potential replacement of the fuel tank vent line; owners should verify their vehicle's recall status.
• The 12-volt battery is a critical maintenance item; proactive replacement every 4-5 years is recommended, as a failing 12V battery can prevent the vehicle from starting .

Understanding the 2017 BMW i3 REX (94 Ah)

The 2017 BMW i3 with Range Extender (REX) represents the "sweet spot" for many owners, featuring the larger 94 Ah (33 kWh) battery pack and 4G telematics . This vehicle pairs a high-voltage battery and electric motor with a small 650cc two-cylinder engine derived from the BMW C650 scooter. The 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. The engine is designed primarily as an emergency backup rather than for continuous use . BMW's Condition Based Service (CBS) system monitors actual vehicle usage—including driving conditions and engine operating hours—to determine maintenance needs, with service reminders displayed through the vehicle's information center.

BMW Factory Warranty and Maintenance Program

The 2017 BMW i3 REX includes comprehensive factory coverage :

The factory maintenance program covers scheduled services during this period, including oil changes and other routine maintenance items as determined by the CBS system. Annual maintenance costs are estimated at $0 for year 1, $90 for year 2, $166 for year 3, and $242 for year 4 .

Engine Oil and Filter Change

Factory Schedule

The REX engine requires oil changes at intervals determined by the CBS system, approximately 10,000 miles or 12 months . The engine operating hours are recorded in the EDME control unit and used to calculate service needs .

Oil Capacity and Specification:

• Capacity: Approximately 2.6 liters for a service fill
• Recommended Oil: 5W-30 or 5W-40 synthetic oil meeting BMW specifications
• Service Interval: CBS-determined (approx. 10,000 miles / 12 months)

Owner Guidance: Many owners and specialists recommend an annual oil change as a conservative measure, particularly given the extended periods between REX engine use . Since oil ages even when not used, some owners change the oil every 1-2 years regardless of mileage . The REX engine averages less than 2 hours of runtime per year for many owners due to the 10-minute maintenance cycle every 60 days .

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.

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 . A brake fluid flush costs approximately $180 at a dealership.

Vehicle Check/Inspection

A comprehensive vehicle check is typically performed at the same 2-year interval as the brake fluid replacement . The CBS system will indicate when this inspection is due.

Transmission Gear Oil

A critically important consideration for the 2017 i3 REX is the transmission gear oil. BMW officially classifies this as a "lifetime fill" and has removed the fill plug, making service more difficult .

Real-World Experience: At 95,000 miles, a 2017 REX owner reported the drained gear oil was dark brown, and the drain plug was covered in sludge and metal shavings, indicating the oil was long overdue for replacement . The owner recommended changing the transmission gear oil every 30,000 miles maximum .

Owner Guidance: Like all oils, transmission gear oil oxidizes over time and loses its lubricating properties. Heat, friction, and contamination will inevitably break it down . Despite BMW's "lifetime" claim, periodic replacement is recommended to extend the gearbox's life. Service requires specialized knowledge, as the fill plug has been removed, requiring axle removal for access.

Spark Plugs

BMW's official documentation 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" .

Parts Information:

• Part Number: 12 12 2 357 197 (BMW) / NGK LMAR8AI-8E
• Quantity: 2 spark plugs

Owner Guidance: While spark plugs are not a scheduled maintenance item, some owners may choose to replace them if experiencing drivetrain errors or misfire codes . The REX engine uses NGK LMAR8AI-8E spark plugs .

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 .

Cabin Air Filter

The cabin air microfilter should be replaced as desired, typically every 12-24 months . This is an owner-serviceable item that can be easily accessed.

Coolant System

There is no recommended cooling fluid change interval in BMW's official documentation . The i3 REX has a third cooling circuit that transfers heat from the REX engine to the main propulsion cooling system .

Owner Guidance: The REX coolant likely experiences higher temperatures than the other coolants, so periodic inspection is prudent . If the coolant expansion tank is damaged, the cooling circuit should be bled and refilled using BMW-approved coolant.

12-Volt Battery

The 12-volt battery is a critical maintenance item for the i3. If the 12V battery fails, the car will not start or may not engage the high-voltage system .

Replacement Interval: Many owners recommend proactive replacement after 4-5 years . Short trips and extreme temperatures can shorten battery life.

Important Safety Recall: 17V-088

Affected Vehicles

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, which in the presence of an ignition source can increase the risk of a fire.

Correction

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

Owner Action: Owners should verify whether this recall has been completed on their vehicle. The recall is performed free of charge at authorized BMW centers.

REX Maintenance Cycle

The REX engine automatically performs a self-maintenance cycle if it has not been used for an extended period—approximately every 60 days. During this cycle, the REX engine runs for about 10 minutes to lubricate internal components and ensure proper operation . This is a normal function and does not require user intervention.

Summary Maintenance Schedule