Why wont my 1997 Tahoe shift into gear when I press down the brake pedal It has automatic transmission.could it be netural safety switch?

It's highly likely the problem is related to the neutral safety switch (NSS), also sometimes called the neutral start switch. This switch prevents the engine from starting unless the transmission is in Park or Neutral. Since your Tahoe won't shift into gear, the same mechanism that prevents starting in gear is likely malfunctioning and preventing shifting.

However, there are a few other possibilities to consider:

* Faulty NSS: This is the most probable cause. The switch might be worn, corroded, or have a broken wire.

* Transmission linkage: The linkage that connects the shifter to the transmission could be broken or adjusted incorrectly. This would prevent the transmission from receiving the correct signal to shift.

* Transmission problems: While less likely given the specific symptom, internal transmission issues *could* prevent shifting. This is more likely to manifest as other issues as well, such as slipping or hard shifting.

* Brake light switch: While less common, a faulty brake light switch *could* be involved if the system uses the brake pedal signal for more than just lighting. It's connected to the safety system, and if that's not functioning correctly, the NSS will not function properly.

* Low Transmission Fluid: Extremely low transmission fluid can lead to bizarre shifting problems.

Troubleshooting Steps:

1. Check the brake lights: Make sure your brake lights work properly. If not, the brake light switch is a suspect.

2. Check the transmission fluid level: Ensure the transmission fluid is at the correct level and condition. Low or dirty fluid can cause many transmission problems.

3. Inspect the linkage: Look under the vehicle (safely!) and visually inspect the linkage connecting the shifter to the transmission. Look for any broken or disconnected parts. This often requires removing underbody coverings.

4. Test the Neutral Safety Switch: This is the most difficult to do without some automotive experience and tools. You'll likely need a multimeter to test for continuity in various positions. This is best done with the help of a repair manual or a qualified mechanic.

5. Have a mechanic diagnose it: The safest and most efficient approach if you lack experience in auto repair is to have a qualified mechanic diagnose and fix the problem.

If you're not comfortable working on your vehicle, it's best to take it to a mechanic immediately to avoid causing further damage. Attempting repairs on a transmission system is not for the inexperienced. A misdiagnosis could lead to very costly repairs.