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BMW 125i F20/F21 N20 / B48

The BMW 125i belongs to the F20/F21 1 Series generation, built approximately 2012–2019. Production moved from the N20 to the B48 engine family at approximately 2015, so the exact engine must be confirmed on each vehicle. Covered body styles are 5-door Hatchback and 3-door Hatchback. Depending on the variant, it was offered with rear-wheel drive or xDrive all-wheel drive, paired with a manual gearbox or an automatic gearbox. Engine management is by a BMW DME; identify the exact ECU hardware and software from the vehicle before ordering a file.

Model & Generation Context

Engine families

N20 → B48

Exact revision is production-date and vehicle-specific

Displacement

2.0L

Production

c. 2012–2019

Approximate; confirm the build date from the vehicle

Fuel Type

Petrol

Supported Model Variants

BMW 125i

Engine: N20

Production: c. 2012–2015

Chassis: F20, F21 · 5-door Hatchback, 3-door Hatchback

Drivetrain: RWD, xDrive

BMW 125i

Engine: B48

Production: c. 2015–2019

Chassis: F20, F21 · 5-door Hatchback, 3-door Hatchback

Drivetrain: RWD, xDrive

Engine and Production Transition

Earlier engine family

N20

Listed production: 2012–2015

ECU: BMW DME — identify from vehicle

Later engine family

B48

Listed production: 2015–2019

ECU: BMW DME — identify from vehicle

Approximate transition period: around 2015. The changeover date varies by market, body style and production date and should not be treated as exact.

The exact engine and ECU must be confirmed from the vehicle before any file is ordered.

Related Application Pages

BMW 1 Series F20/F21 B48 Models

Other variants sharing this engine family and chassis

Engine Platform

BMW N20 Engine Hub

Platform overview, tuning paths, reliability notes and diagnostics

BMW B48 Engine Hub

Platform overview, tuning paths, reliability notes and diagnostics

All BMW N20 Models

Every model in the directory using the N20 engine

All BMW B48 Models

Every model in the directory using the B48 engine

ECU & Transmission Context

BMW DME — identify from vehicle

Read the ECU hardware and software numbers from the vehicle before ordering a file.

Manual gearbox

Gearbox specification is vehicle-specific; confirm it from the vehicle order data.

Automatic gearbox

Gearbox specification is vehicle-specific; confirm it from the vehicle order data.

Identification & Pre-Tuning Checks

  • This model was built with more than one engine family (N20 and B48); confirm the engine code on the vehicle before ordering a file.
  • The exact engine revision is production-date and vehicle-specific; it is not inferred from the model name.
  • Identify the BMW DME and its exact hardware and software version from the vehicle; it is not inferred from the model name.
  • Scan for stored fault codes and resolve existing issues before any calibration work.
  • Gearbox type varies on this model; note whether the car is manual or automatic when submitting a file.

Available Service Paths

Stage 1 Calibration File

A vehicle-specific calibration for a healthy engine on standard hardware. Includes ECU file review, fuel and hardware assessment.

Request a Stage 1 File

Stage 2 Calibration Review

Review your supporting hardware, thermal setup and fuel configuration before requesting an upgraded calibration file.

Review My Stage 2 Setup

Custom Calibration and Datalog Review

Submit datalogs and vehicle configuration for a fully custom calibration review tailored to your specific setup.

Request a Custom Calibration

ECU Read and Support Check

Verify your ECU hardware and software version is supported before starting a calibration project.

Check ECU Support

TCU Calibration Assessment

Assess transmission control unit compatibility and calibration options for your vehicle and gearbox configuration.

Request a TCU File

Pops and Bangs Request Review

Submit a request for review. Availability depends on vehicle setup, hardware configuration and local road-use requirements.

Availability depends on vehicle setup, hardware and local road-use requirements. Not available for all configurations.

Submit for Review

Related Resources

BMW Pre-Tuning ChecklistStage 1 vs Stage 2 ExplainedWhen to Diagnose Before TuningBMW Petrol Tuning Guide

BMW N20 File Service

Order a file for your BMW 125i

Prepare the original ECU file, vehicle details, fuel and hardware setup before opening a file request.

Open File Service Portal

Original ECU File

Read via OBD, Bench or Boot

Vehicle Details

Model, year and specification

Fuel Information

Fuel type and octane rating

ECU Identification

Hardware and software version