B12C5 Engine start/stop switch failure (Honda, Acura)

Start/stop button failure, car may not start

B12C5 in short

On Honda and Acura, B12C5 means the engine start/stop switch has failed. The car may not start on the first press, and the display may show a message. Honda extended warranty on some Fit, HR-V and Acura NSX models. It is usually safe to drive, but have it checked soon so you are not stranded.

The start/stop button is a switch that the computer reads each time you press it. B12C5 is stored when the computer decides the switch itself has failed.

Honda bulletins and owner letters from late 2020 and early 2021 cover 2015 to 2017 Fits, 2016 to 2018 HR-Vs and the 2017 Acura NSX. They extend warranty coverage for the keyless start system on these cars.

One HR-V service record describes a car that fails to start or stop on a single press.

Pick your make

B12C5 is a manufacturer-specific code: its meaning depends on who built the car.

Other makes: meaning not verified. Check with a scan tool that reads manufacturer definitions.

Most likely causes

  1. Engine start/stop switch

    Supported by vehicle data
    Why it ranks here
    Honda and Acura bulletins and owner letters name B12C5 as an engine start/stop switch failure, and HR-V complaints quote dealers replacing the switch.
    What would change this
    Rises if the button needs repeated presses and the key fob battery is good. Falls if a new switch does not clear the code.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read the stored codes with a scan tool and note any message on the display.

    Low riskTool: OBD-II scan tool

    • IfB12C5 is stored

      It meansHonda and Acura bulletins treat this as a start/stop switch failure.

      Go to step 2

  2. Give your VIN to a Honda or Acura dealer and ask whether the keyless start warranty extension covers your car.

    Low risk

Symptoms

  • Start/stop button needs several presses before the engine starts
  • Warning message on the display
  • Car will not start at all Gets more serious: stop and have it checked.

How to fix

  1. Ask a Honda or Acura dealer whether the keyless start warranty extension covers your VIN before paying for the switch.

Parts and cost context

  • Engine start/stop switch:Honda extended warranty on some models, so check coverage first. Labour varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Honda

  • 2016–2018 · HR-V

    Supported by vehicle data

    Honda extended warranty on the keyless start system for B12C5, and an HR-V owner reports the switch replaced after the car stopped starting reliably. Whether the extension still applies is not verified.

  • A20-098Status unverified

    Start/stop switch failure, DTC B12C5

    2015–2017fit · issued · NHTSA 10184317

    Warranty extension for the keyless start system on Fit models that may not start on the first press.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

No curated relationships for B12C5 yet.

All Body electrical codes

Sources and review

  1. Honda A20-098: vehicle may not start on first press of the ENGINE START/STOP button, DTC B12C5 (Engine Start/Stop Switch Failure); warranty extension (2015-2017 Fit) — American Honda Motor Co. ,
  2. NHTSA complaint ODI 1666455 (2017 Honda HR-V) — NHTSA Office of Defects Investigation
  3. Honda owner notification letter: may not start on first press of ENGINE START/STOP, DTC B12C5; warranty extended (2016-2018 HR-V) — American Honda Motor Co. ,
  4. Acura B20-050: vehicle may not start on first press of ENGINE START/STOP, DTC B12C5; warranty extended (2017 NSX) — American Honda Motor Co. ,
  5. Acura owner notification letter: may not start on first press of ENGINE START/STOP, DTC B12C5; warranty extended (2017 NSX) — American Honda Motor Co. ,
Last reviewed
Written by
Saurabh K.
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Used once to identify your engine; not stored.