When starting a vehicle, if the automatic transmission is not in neutral or park, the neutral safety switch will prevent the engine from starting.
How does the neutral safety switch work?
To protect the vehicle, there is a switch installed on most automatic and dual clutch transmissions which disallows the engine from starting when the transmission is not placed in neutral or park. Some models use input from the transmission control unit to determine the vehicle's transmission position, but others use a physical switch. Both systems function to interrupt the starting circuit when the transmission is not in park or neutral.
If the engine will not turn over with the key in the start position, the Neutral Safety Switch may need to be replaced.
What are the symptoms related to a bad neutral safety switch?
When the neutral safety switch fails, the vehicle will either start in any gear, or will not start in any gear. In many cases, the vehicle will start in neutral, but not in park. Some vehicles may store on-board diagnostic (OBD) trouble codes which reference the transmission, but, most commonly, there will be no diagnostic trouble codes stored in the vehicle's memory for this issue, as the computer cannot recognize this failure in most cases.
Can I drive with a neutral safety switch problem?
Driving with a faulty neutral safety switch is generally impossible , but if the vehicle will start and change gears like normal, driving should not pose any issues. If the vehicle will not start, it will require a tow to a repair facility.
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How often do neutral safety switches need to be replaced?
MAF sensors do tend to fail sometime in many vehicles. Failure rates are highest between 100,000 and 150,000 miles, but this is only an average. The sensor can also be damaged by road debris in many vehicles, or anytime the transmission is serviced or repaired. Lastly, a collision may cause a physical or electrical fault in the neutral safety switch. Vehicles with internal neutral safety switches will benefit from proper maintenance, and may fail prematurely when the transmission is neglected.
How are neutral safety switch issues diagnosed?
The neutral safety switch is quickly diagnosed by testing the switch, and related components attached to the gear selector inside the vehicle. A faulty neutral safety switch will most likely be removed and bench tested for confirmation of failure.
It is important to properly diagnose any no-start issues. A dead battery, starter, or other components may prevent an engine from turning over. The Neutral Safety Switch is only one possibility.
How is a neutral safety switch replaced?
Replacement of a steering knuckle on most vehicles is an advanced DIY repair that requires tools, equipment, and experience necessary to remove pressed hubs and bearings (including snap rings that retain the bearings), and to press the components into the new steering knuckle. The ball joints and tie rod end also need to be separated. The vehicle needs to be safely lifted in the air with a jack and jack stands to perform this repair. If you are not comfortable with these repair procedures, it would be wise to find a professional technician for the job.
When replacing the Neutral Safety Switch, proper adjustment of the new switch is critical.