Audi A4 B9 Fuses: Complete Guide 2015-2023

BySerge Barrett

The Audi A4 B9 (2015–2023) uses a sophisticated multi-box fuse and relay architecture to protect its extensive electrical systems. Understanding the exact location, amperage and function of every fuse is essential for diagnosing electrical faults, adding accessories or replacing blown components without damaging control units. This guide covers every fuse box on the B9 platform, including the dashboard fuse carrier, the battery fuse carrier in the engine bay and the additional relay/fuse panels found on certain variants.

Fuse Box Locations on the Audi A4 B9

The B9 A4 has three primary fuse locations:

  • Fuse carrier in the dashboard (left side, driver footwell) – main cabin fuses, accessible by removing the lower trim panel
  • Battery fuse carrier in the engine compartment (near the battery on the right strut tower) – high-current fuses and main supply lines
  • Fuse carrier behind the glove box / right footwell area – supplementary fuses for ADAS, MMI and comfort systems (present on higher specification vehicles)

Dashboard Fuse Carrier – Full Fuse List

  • SB1 – 5A – Instrument cluster, speedometer
  • SB2 – 5A – Interior lighting, ambient light control
  • SB3 – 5A – Rain/light sensor, auto-dimming mirror
  • SB4 – 10A – Steering column electronics, steering angle sensor
  • SB5 – 5A – Gateway control unit (J533)
  • SB6 – 5A – Diagnostic interface, OBD-II port power
  • SB7 – 10A – Airbag control unit (J234)
  • SB8 – 5A – Driver door control unit
  • SB9 – 5A – Passenger door control unit
  • SB10 – 5A – Rear left door control unit
  • SB11 – 5A – Rear right door control unit
  • SB12 – 10A – Central locking, luggage compartment release
  • SB13 – 20A – Front windscreen wiper motor
  • SB14 – 5A – Wiper interval relay, rain sensor supply
  • SB15 – 10A – Horn
  • SB16 – 5A – Climatronic / climate control unit
  • SB17 – 10A – Blower motor control unit (final stage)
  • SB18 – 30A – Blower motor
  • SB19 – 5A – Sunroof/panoramic roof control module
  • SB20 – 20A – Sunroof/panoramic roof motor
  • SB21 – 10A – Seat heating, driver
  • SB22 – 10A – Seat heating, passenger
  • SB23 – 5A – Steering wheel heating
  • SB24 – 5A – Virtual Cockpit / digital instrument display
  • SB25 – 5A – Head-up display (HUD) unit
  • SB26 – 10A – MMI navigation plus, infotainment unit
  • SB27 – 5A – Amplifier, Bang & Olufsen / standard audio
  • SB28 – 10A – Telephone, Bluetooth module
  • SB29 – 5A – TV tuner / antenna amplifier
  • SB30 – 10A – Reversing camera, parking aid control unit
  • SB31 – 5A – Adaptive cruise control (ACC) sensor
  • SB32 – 5A – Lane assist, side assist control units
  • SB33 – 10A – Electric power steering (J500)
  • SB34 – 5A – Start-stop system, belt tensioner control
  • SB35 – 20A – Cigarette lighter / 12V socket, front
  • SB36 – 20A – 12V socket, rear / centre console
  • SB37 – 5A – Interior rear-view camera (optional)
  • SB38 – 10A – Adaptive damper control (DCC) unit
  • SB39 – 5A – Audi drive select module
  • SB40 – 5A – Night vision / thermal imaging camera (optional)

Engine Compartment Battery Fuse Carrier – Full Fuse List

  • SA1 – 80A – ABS/ESP hydraulic pump motor
  • SA2 – 60A – Power steering pump (electric motor, 2.0 TFSI)
  • SA3 – 40A – Engine control unit (ECU) main supply
  • SA4 – 30A – Fuel pump relay, high-pressure pump supply
  • SA5 – 40A – Cooling fan, main speed stage
  • SA6 – 30A – Cooling fan, secondary speed
  • SA7 – 30A – Radiator shutter / active grille control
  • SA8 – 40A – Alternator excitation / voltage regulator
  • SA9 – 20A – Lambda sensors, exhaust temperature sensors
  • SA10 – 20A – Ignition coils supply
  • SA11 – 10A – Throttle body, electronic throttle
  • SA12 – 10A – Camshaft adjustment valves (TFSI engines)
  • SA13 – 15A – Injectors (petrol engines)
  • SA14 – 20A – Glow plugs relay (diesel TDI engines)
  • SA15 – 30A – Diesel particulate filter (DPF) heating element
  • SA16 – 20A – AdBlue/SCR dosing unit (3.0 TDI)
  • SA17 – 10A – Turbocharger wastegate solenoid
  • SA18 – 10A – Secondary air pump
  • SA19 – 30A – Starter motor relay
  • SA20 – 40A – Main fuse, battery positive terminal feed
  • SA21 – 30A – Heated windscreen washer jets
  • SA22 – 20A – Headlight cleaning system pump
  • SA23 – 30A – Rear window demister
  • SA24 – 20A – Heated front windscreen (optional)
  • SA25 – 5A – Under-bonnet lighting

Right Footwell / Behind Glove Box Fuse Carrier – Full Fuse List

  • SC1 – 5A – Front camera (lane keep assist)
  • SC2 – 5A – Radar sensor, front (ACC)
  • SC3 – 5A – Radar sensor, rear left (blind spot)
  • SC4 – 5A – Radar sensor, rear right (blind spot)
  • SC5 – 10A – Driver assistance systems central module
  • SC6 – 5A – eCall / emergency call module
  • SC7 – 5A – Audi connect, SIM/LTE module
  • SC8 – 10A – Wireless phone charger (optional)
  • SC9 – 5A – USB hub, front
  • SC10 – 5A – USB hub, rear
  • SC11 – 10A – Electric parking brake (EPB) motor
  • SC12 – 5A – Brake booster vacuum sensor

How to Identify a Blown Fuse on the Audi A4 B9

Always switch the ignition off before inspecting fuses. Use the fuse extraction tool stored inside the dashboard fuse carrier lid. Visually inspect the metal bridge inside each fuse – a break or discolouration confirms failure. Use a multimeter set to continuity or DC voltage (12V on one terminal with ignition on, 0V on the other confirms a blown fuse). Never replace a fuse with a higher amperage rating than specified – this risks wiring damage or fire. If a replacement fuse blows immediately, a short circuit exists in that circuit and must be diagnosed before fitting another fuse.

Fuse Box Diagram Location in the Vehicle Documentation

The official fuse assignment chart is printed on the inside of the dashboard fuse carrier cover and in the Owner’s Manual, Chapter ‘Technical data – Fuses’. On B9 models from 2019 onward with the updated MMI system, the fuse list is also accessible via Menu > Vehicle > Service > Fuse assignment on the infotainment screen.

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