Disconnect and Reconnect the Battery

Disconnecting the 12 V battery on your Subaru WRX / WRX STI (2015–2021) — the VA generation — is a job most owners can do on the driveway with a single spanner. You’ll need it for battery renewal, before winter storage, when working near the airbags or seat-belt pretensioners, or to recover the electrical system after a flat. The VA carries plenty of electronics — the digital dash, the infotainment head unit, the memory in the engine and transmission control units — so it will drop a few learned settings when the power is cut. That is completely normal. Take the terminals off and put them back in the right order and the car relearns everything cleanly, usually within a short drive.

Where the 12 V Battery Is

The 12 V battery sits in the engine compartment, usually toward one front corner and often under a plastic cover or trim panel. Lift the bonnet, prop it securely, and look for the two terminals. The negative (−) post wears a black cap or lead and carries the earth strap that bolts to the body or engine; the positive (+) post is capped red and feeds the main harness. Identify both before you touch anything — getting them the right way round is what keeps the job simple and safe.

Before You Start

• Switch the ignition fully off, take the key well clear of the car, and close the doors so nothing wakes the electrics back up.
• Turn off the lights, climate fan, heated seats and stereo so there’s no load on the system.
• Note down your radio station presets and any personal settings you’d rather not re-enter from scratch.
• Give the car a couple of minutes with everything off so the control modules power down before you pull a terminal.
• Have the correct spanner ready, plus gloves and eye protection — a battery can arc if a spanner bridges the posts.

Disconnecting

1. Confirm the ignition is off and everything electrical is switched off.
2. Loosen the clamp on the negative (−) terminal first and lift the lead clear, tucking it aside so it can’t spring back onto the post.
3. Now loosen and remove the positive (+) terminal.
4. If you’re working near the airbags or seat-belt pretensioners, wait a couple of minutes after disconnecting before starting that work, so any stored charge in the restraint system has bled away.

Reconnecting

1. Fit the positive (+) terminal first and nip the clamp up snug.
2. Fit the negative (−) terminal last and tighten it.
3. Check both clamps are firm — a loose earth is the usual cause of odd faults afterwards — then refit any cover.

What You’ll Need to Reset Afterwards

With power restored, a handful of learned settings need to come back:

• Clock and radio — re-enter the time and your station presets.
• Power windows — if one-touch up/down stops working, hold the switch fully up until the glass tops out and hold a moment, then fully down and hold, to relearn the limits.
• Steering-angle and stability control — these settle after a short drive with some gentle steering; a VDC or steering light usually self-clears once they do.
• Engine idle — the turbo boxer may idle or pull slightly differently for the first few miles as the ECU relearns its trims; this smooths out on its own.

If a Warning Light Stays On or the Car Feels Off

• Recheck that both clamps are tight and clean, especially the negative earth.
• Drive a few gentle miles so the steering, stability and idle relearns can complete.
• Repeat the window one-touch relearn if it didn’t take the first time.
• If a light is stubborn, rule out a genuinely tired or flat battery — a weak one throws odd faults.
• Read any stored trouble code and look it up on autodtcs.com.

Frequently Asked Questions

Where is the battery on a Subaru WRX?

In the engine compartment, typically toward a front corner and often under a cover. Raise the bonnet and look for the red-capped positive post and the black negative post.

Which terminal do I disconnect first?

The negative (−) terminal comes off first and goes back on last. On reconnection the positive (+) goes on first. Doing it this way avoids a short if a spanner touches bodywork.

What needs resetting after I reconnect?

Mainly the clock and radio presets, the one-touch window function, and a short settling period for the steering-angle, stability control and engine idle. Most of it clears itself within a few miles of normal driving.

Does a new battery need coding on the WRX?

A like-for-like replacement of the correct size and type generally needs no coding. Fit the same specification as came out; if your car has stop-start, match the AGM or EFB type it was built with.

Will disconnecting the battery clear fault codes or the service light?

It can clear some temporary codes, but it is not a proper service-light reset and it won’t fix an underlying fault — the code simply returns if the problem is still there. Diagnose the cause rather than relying on a power cut.

Can I jump-start it instead of disconnecting?

If the aim is just to recover a flat, a jump-start avoids losing your settings. Disconnecting is only necessary when you’re renewing the battery or working near the airbags and electrics.

If a warning light stays on after reconnecting, read the stored code and look it up on autodtcs.com.