2002 Trailblazer XLT 2 wheel drive

I think it’s more than just a single sensor. Indeed, while a sensor problem may keep the transmission from functioning fully, it is more than likely that a bad sensor would put the transmission into limp-home mode so that you would have at least one gear functioning fully to enable you to get to a service area. If two sensors have gone bad, it indicates to me, that there may be an electronic problem that has to be diagnosed, which can be an expensive proposition.

Of course, you do have a leg-up in finding an electronic fault, the OBD-II diagnostic scanner. Using the scanner, you get a full readout of the health of your SUV’s drivetrain — engine, transmission and related components. The readout also shows a number of fault codes. Those codes are important because they pinpoint the areas where the trouble exists.

The one issue that some have with fault codes is that they are not comprehensive enough to give you an exact cause. Instead, they give you a general cause and point to the area of the problem. This is better than the situation just a few years ago when you only received one or two trouble codes that pointed to the transmission or sensors. It is vastly improved.

The improvement is such that I recommend an OBD-II scan first from which you should receive a good idea of exactly what is going on.

Off the top of my head, given what you have described, I would think the problem could be in the clutches/bands and/or the torque converter, gearing, clutches and bands. If the problem is what I suspect it is — major component failure that only a teardown can confirm — then your only solution is dropping in a rebuilt transmission. If you are planning to keep the Trailblazer for at least two to four years more then it is worth the $3,200 to $3,400 you will be investing for the rebuilt unit. However, if you are planning to get out of the Trailblazer and into something a little newer then I would suggest getting it to a dealership so you can use it as a trade. That’s probably the best thing for it.

I know you probably wanted to hear something else, but, I am being honest with you. The good news is that my answer isn’t totally negative as the OBD-II scan could identify the issue and it may just be a combination of sensors and solenoids. If that is the case, then fixing those problems, likely to cost about $800, a lot less than replacing the whole thing. You won’t know what the problem is until you have the scan done. So I think you should make it a priority. Please let me know what is ultimately ailing your tranny.