Where is the main relay on a Subaru Impreza?
The main relay in most Subaru Impreza models is located inside the vehicle, not in the engine bay. It powers the engine-control unit (ECU) and fuel pump, and a failure can lead to a no-start or intermittent starting problems. This guide explains where to look and how to verify its function.
What the main relay does
The main relay (often labeled M-relay or MAIN) supplies power to critical engine-management components when the ignition is on. If it fails, the ECU and other vital systems may not receive power, causing the car not to start or to stall unexpectedly. Understanding its role helps explain why locating and testing it matters during a no-start diagnosis.
Where to look for the main relay in an Impreza
In most Impreza models, the main relay resides in the interior fuse/relay box rather than the engine bay. The exact location can vary by year and market, but two common spots are:
- Behind the glove box on the passenger side, inside the interior fuse/relay box. This is typically the most common setup for many U.S.-market Impreza models from the late 1990s onward.
- Under-dash area on the driver's side knee panel or a nearby lower dash panel, in an additional fuse/relay block. Some early or non-U.S. variants use this location.
Because layouts can differ by year and trim, consult the owner’s manual or service diagram for your exact vehicle. When inspecting, ensure the ignition is off and the battery is disconnected before handling any interior fuse panels.
Model-specific notes
Exact placement can vary between generations and markets. If you’re unsure, refer to the factory diagrams or a reputable repair guide for your year range, or ask a Subaru technician for the precise location on your specific car.
How to identify and access the main relay safely
Access typically involves removing a small panel or door to reveal the interior fuse/relay box. Take precautions to avoid shorts or shocks, and use the correct tools to prevent damaging plastic covers or wiring.
- Turn the ignition off, remove the key, and engage the parking brake.
- Disconnect the negative battery terminal to prevent accidental short circuits.
- Open the interior fuse/relay box area (glove box side or knee panel) and locate the relay labeled M, MAIN, or ECU, per the diagram on the panel cover.
- Inspect for signs of damage, such as melted plastic, corrosion, or bent pins. If in doubt, test with a multimeter or swap with a known-good relay of the same rating.
- If swapping resolves the issue, replace the faulty relay and reassemble. Reconnect the battery and perform a test start.
- If the problem persists after replacement, broaden diagnostics to the ECU, fuel pump, or wiring harness, or seek professional help.
Note that some symptoms may mimic other component failures. A systematic approach helps confirm whether the relay is the root cause or if another system is involved.
What to do if you can't locate the relay
If you cannot find the relay by inspection, consult the owner's manual, a factory service manual, or a Subaru dealer. Community forums and model-specific guides often include labeled diagrams for the exact year and market of your Impreza.
Summary
The main relay on a Subaru Impreza is generally found inside the interior fuse/relay box, commonly behind the glove box on the passenger side or in an under-dash knee panel on the driver’s side. Locating and testing this relay is a key step when diagnosing starting or ECU-power issues. If you’re unsure about the location or procedure, seek guidance from a qualified technician or official manuals.
