what gear can you not start a car in

[JosiahMarie]

You cannot start a car in any forward or reverse gear; it must be in Park (P) for automatics or Neutral (N) with the clutch fully depressed for manuals. Attempting to start the engine while in a drive gear is a primary safety feature designed to prevent the vehicle from lurching forward or backward unexpectedly, which could cause an accident. This is managed by a critical component called the neutral safety switch.

In an automatic transmission, the Park position locks the transmission's output shaft, physically preventing the wheels from turning. Starting in Neutral is also typically possible, but Park is the standard and safest choice. For manual transmission vehicles, the clutch pedal must be pressed completely to the floor. This action activates a clutch safety switch that interrupts the starter circuit, ensuring the car can only start when the connection between the engine and wheels is disengaged.

Trying to start the car in gear often results in nothing happening—no cranking sound—as the safety switches do their job. If your car does start while in gear, it indicates a malfunctioning safety switch, which is a significant hazard that requires immediate repair by a qualified mechanic. The system is designed to protect you, your passengers, and anyone nearby.

The reliability of this safety mechanism is well-documented. The following table outlines common scenarios and outcomes based on data from vehicle service incidents.

Scenario (Transmission Type)	Gear/Clutch Position	Expected Result	Typical Repair Cost for Switch Failure (USD)
Automatic	Park (P) or Neutral (N)	Engine Starts Normally	-
Automatic	Drive (D), Reverse (R), etc.	No Cranking / No Start	$125 - $300
Manual	Clutch Depressed (Any Gear)	Engine Starts Normally	-
Manual	Clutch Not Depressed	No Cranking / No Start	$80 - $200
Faulty Switch (Any Type)	Any Position	Engine May Start in Gear	$100 - $350

[OmarRose]

Look, it's simple: just keep it in Park. That's what it's for. On my old automatic, if I accidentally bump the shifter out of Park, the key won't even turn. It's a built-in "don't be stupid" feature. My dad learned the hard way years ago on his manual truck—he forgot the clutch and the whole thing jumped and stalled in the driveway. Scared him half to death. So, Park for automatics, clutch in for sticks. Always.

[McDylan]

From an engineering perspective, the prohibition is a fundamental safety interlock. Starting in a drive gear would apply immediate torque to the wheels, causing an uncontrolled launch. The neutral safety switch in automatics and the clutch initiation switch in manuals are simple but critical components that complete the starter motor circuit only under safe conditions. This prevents undue stress on the starter motor and the transmission itself, avoiding potential damage and ensuring predictable vehicle behavior upon ignition.