Push-button start does nothing: brake switch, fob or module

Press the button and nothing happens — no crank, no click, sometimes not even a dashboard response. That is a different problem from an engine that turns and does not fire.

Related: car won’t start diagnosis.

What must be true before it will crank

A push-button start checks several conditions, and any one of them failing produces silence:

1. The key is detected inside the cabin.
2. The brake pedal is pressed — or the clutch, on a manual.
3. The transmission is in Park or Neutral.
4. The immobiliser has authorised starting.
5. The battery can supply cranking current.

Silence usually means one of those five, not a failed starter.

The brake switch

The most common cause, and one of the cheapest.

The system requires the brake pedal pressed before it will start. If the switch does not report that, nothing happens.

The free test: look at the stop lamps. If they do not illuminate when you press the pedal, the switch is the fault — and you have found it without tools.

Two specific causes:

A missing pedal pad. Many vehicles have a small rubber or plastic pad on the pedal arm that the switch plunger rests against. It degrades and falls out, often found on the footwell carpet. Without it the switch reads permanently pressed, which also drains the battery through the stop lamps.

Adjustment drift. The switch is adjustable, and the bracket flexes over years.

P0571 brake switch circuit and P0703 and P0706 brake switch and range sensor.

The key not detected

Try the emergency method. Nearly every keyless vehicle can start with a dead fob battery by holding the fob against a marked location — the start button itself, a spot on the steering column, or a cubby in the centre console.

Find out where that is on your car now, while parked at home.

Causes of non-detection:

• A flat fob battery: key fob range dropped.
• Interference inside the cabin — a phone or a charger next to the fob.
• A failed interior aerial.
• A dead spot in the detection zone; try moving the key.

Transmission not in Park

On an automatic, the range switch must report Park or Neutral.

Try Neutral instead of Park. If it starts, the range switch is misadjusted or failing — a diagnosis in five seconds: P0705 transmission range sensor.

On a manual, the clutch switch must report the pedal fully down. Press it right to the floor.

The immobiliser

The tell: a security or key symbol on the dashboard. That is the system explicitly saying it does not recognise the key.

Car won’t start: immobiliser troubleshooting and immobiliser key learning per brand.

The vehicle battery

A battery too flat to crank can also be too flat to run the modules that decide whether to try.

The signature: complete silence, and dashboard lights that dim or do not illuminate. Different from rapid clicking, which means the battery has some charge but not enough.

How to jump start a car correctly and battery terminals corrosion.

On a car with a start button, jump starting still works — locate the designated jump points, which on many vehicles are not the battery itself.

The button

Least common, but it is a switch pressed thousands of times. Contacts wear.

The tell: it works sometimes, or works if pressed harder or held longer.

In what order

1. Look at the stop lamps while pressing the brake pedal.
2. Check for a security lamp on the dashboard.
3. Try Neutral instead of Park.
4. Hold the fob against the emergency position.
5. Check the dashboard lights — dim or absent means battery.
6. Check for the pedal pad in the footwell.
7. Press the button firmly and hold if it is intermittent.

Check battery voltage and brake switch status — an ELM327 adapter and the free tier of the app are all it takes. Those two readings cover the two most common causes of a start button that does nothing.