BMW 135i Relay Location Guide: Fuse Box and Relay Positions Explained

BMW 135i Relay Location Guide

The BMW 135i relay location guide helps you identify where key relays sit in the car and what systems they support.

If you are tracking down a no-start issue, fuel pump problem, or accessory fault, knowing the relay layout can save time and prevent guesswork.

The 135i uses a mix of front and rear electrical distribution points, so the relay you need is not always in the same place as the fuse that protects the circuit.

Understanding that layout is the fastest way to diagnose common electrical complaints.

Where Are the Main Relay Locations in a BMW 135i?

On the BMW 135i, relays are typically found in a few core areas depending on model year and chassis generation.

The most important locations are the front fuse and relay distribution area, the glove box fuse panel, and the luggage compartment electronics area.

• Engine bay distribution box: Often contains relays for power management and high-load engine circuits.
• Glove box fuse panel: Common location for interior electrical protection and some control relays.
• Trunk or rear electronics area: May house relays or integrated control modules related to body electronics.

BMW often integrates relays into modules rather than using standalone plug-in relays, especially on later vehicles.

That means a “relay problem” may point to a module, wiring, or fuse issue rather than a single removable part.

How to Access the Fuse and Relay Areas

Glove Box Area

Open the glove box and locate the fuse access panel or trim cover.

On many BMW 1 Series models, the fuse layout is behind or near the glove box, and related relay components may be adjacent to that area.

Before removing anything, turn the ignition off and wait a few minutes for the vehicle to enter sleep mode.

This reduces the chance of setting fault codes or waking modules while you work.

Engine Bay Area

Lift the hood and look for the power distribution box near the battery positive terminal or along the rear side of the engine bay, depending on engine and production year.

This is where you are likely to find high-current electrical components tied to the DME, fuel system, or cooling system.

Rear Electronics Area

Some BMW 135i models place electrical control units and related relays in the trunk area, often behind trim panels.

This area can be important when chasing issues with central locking, lighting, or power supply faults.

What Do the Relays Control?

Relay assignments vary by chassis, engine, and option package, but several systems commonly depend on relay-controlled power delivery.

If one of these systems fails intermittently, the relay should be part of your inspection.

• Fuel pump circuit: A faulty fuel pump relay can cause long crank, no-start, or stalling symptoms.
• Starter circuit: Starter relay issues may create a no-crank condition even when the battery is healthy.
• Cooling fan operation: The cooling system may rely on relays or integrated control stages.
• Ignition and accessory power: Interior electronics, radio power, and convenience features can be affected by relay or module faults.
• DME and power supply circuits: The digital motor electronics system depends on stable electrical supply for proper engine management.

In BMW terminology, the DME is the engine control unit, and electrical supply faults here can mimic sensor problems, ignition problems, or fuel delivery failure.

How to Identify a Bad Relay

A relay can fail mechanically or electrically.

Common signs include clicking without activation, intermittent operation, melted terminals, or systems that work only when the relay is tapped.

Look for these symptoms:

• Intermittent no-start: The engine cranks but does not fire consistently.
• No power to a specific circuit: A system such as the fuel pump or blower fan stops working.
• Random cutouts: Electrical accessories fail and return without warning.
• Heat damage: Discolored plastic or burnt contacts indicate excess resistance or overload.

If a relay is suspected, compare it with a matching relay in another circuit only if the part numbers and amperage ratings are the same.

Swapping the wrong relay can create more problems or damage a protected circuit.

Relay Location Versus Fuse Location

Fuses and relays are related but not interchangeable.

A fuse protects the circuit from overcurrent, while a relay acts as an electrically controlled switch that sends power to the load.

In BMW electrical troubleshooting, both must be checked.

For example, if the fuel pump does not run, the fuse may be intact while the relay, control module, wiring, or pump itself is faulty.

A visual fuse inspection alone will not confirm that the relay side of the circuit is working correctly.

Best Tools for Diagnosing BMW 135i Relay Problems

You do not need a full workshop to begin diagnosis, but a few tools make the process much easier.

A digital multimeter, test light, and BMW-capable scan tool are the most useful starting points.

• Digital multimeter: Checks voltage, continuity, and ground quality.
• Test light: Helps verify power delivery under load.
• OBD2 scan tool: Reads fault codes from engine and body modules.
• Relay diagram or fuse chart: Confirms which circuit is assigned to each slot.

BMW diagnostic software such as ISTA can be especially helpful because it may identify power supply faults, control module communication issues, or relay-related activation problems.

What If the Relay Is Not a Separate Part?

Many BMW 135i electrical systems use integrated control units instead of traditional plug-in relays.

In that case, the relay function may be built into a junction box, fuse carrier, or body module.

If a circuit fails and no standalone relay is present, check the following:

• Related fuses and fusible links
• Battery condition and charging voltage
• Ground points and corrosion
• Harness damage near the affected component
• Fault codes stored in the DME or body module

This approach is important on modern BMWs because a missing relay slot does not always mean the circuit is simple.

The vehicle may be using solid-state switching or module-based control instead.

Common Symptoms Linked to Relay or Power Supply Faults

Electrical issues in the BMW 135i often show up as drivability complaints before a warning light appears.

Paying attention to patterns can help you narrow the fault quickly.

• Engine starts only after multiple key cycles
• Fuel pump primes inconsistently
• Starter clicks but does not engage
• Dashboard warnings appear and disappear
• Interior electronics reset unexpectedly
• Cooling fan runs at the wrong time or not at all

Because BMW uses sophisticated electronic power management, a weak battery or poor ground can imitate relay failure.

Always test the battery and charging system before replacing parts.

How to Use the Relay Location Guide Safely

When working on the BMW 135i relay layout, disconnect the battery only if the repair requires it and you understand the vehicle’s power management system.

Avoid forcing connectors, and never bypass a relay unless you are performing a controlled diagnostic test.

Label removed relays and covers so they go back in the correct position.

If you are unsure about a relay’s function, use the owner’s manual, factory wiring diagram, or BMW service information before replacing it.

A careful relay inspection combined with fuse testing, voltage checks, and scan data is usually the fastest path to finding the root cause in a BMW 135i electrical issue.