2004 Tahoe Transmission/Harness Replaced – Shifter Problem

This sounds like a problem with the shifter itself. There are any number of reasons that this might be happening. Here’s a list of the possibilities:

— A shifter problem: It’s possible that the shift mechanism could be wearing out and needs to be replaced. It might keep your transmission stuck in Park and not shifting at all. You may need to have the shifter mechanism replaced.

— A shifter lock problem: When you slam the shift into Park, you not only set the pawl that locks the output shaft and keeps the transmission from spinning, but you also effectively lock the shifter as a special lock engages. The lock usually releases when you press the brake after you start, but sometimes it doesn’t. It’s a fairly easy fix that involves popping the tab of the shift lock override unit and pressing the button beneath, while your foot’s on the brake. Your shift will slide out of park and you will be able to start but you will have to get to a service area before you can engage Park again. The override unit is the tiny button-like access panel you will find on the gearshift console near the unit.

— A neutral-start problem: The switch might be wearing out. This switch, which works with the shift interlock solenoid, requires you to press the brake before you can release the shifter. This could be sticky or the solenoid could be failing. Also, there might be a wiring problem.

— A shift interlock solenoid problem: The shift interlock solenoid which requires you to press the brake before you can engage the shifter may be failing. It might be a wiring problem or a problem with the solenoid itself. It’s something that you should have your mechanic check.

— A gearshift cable problem: The gearshift cable may be stretched and may, at times, bind, preventing the necessary take-up so that you can shift out of Park.

As you can see, there are a bunch of possible problems that may be affecting your SUV. For my money, I would check the gearshift cable and the interlock solenoid. Either one can cause the problem you describe — as can the others but not so intermittently — and can keep your transmission locked up.