No Reverse: 2002 GMC Envoy SLT

Here’s the good news, your Envoy is still running and still shifting, in a manner of speaking. But, it’s a big one, there’s a lot wrong with its transmission.

For starters, it sounds like the tranny has gone into limp-home mode. In limp-home mode, you normally lose reverse and most forward gears. Your Envoy will run, after a fashion, but will perform poorly, at best. Symptoms of limp-home include everything you’ve described. Even your statement that the Envoy seems to be revving fits in with this diagnosis.

Your next step would normally be a trip to the local independent transmission shop for a look-see and diagnosis. Since, however, you are looking to save a bit, it might be a good idea at this point to see if you can borrow the diagnostic scanner for your SUV. If you can, put the sensor end into the OBD-II connector on the driver-side of the instrument panel. The OBD-II is located in the area of the kick panel.

Once everything is set up correctly, see if the electronic control module (ECM) has picked up any hard error codes. Hard error codes, like P1700, for example, are generated every time your car’s various computer-controlled systems detect a problem. If the error is serious enough then your SUV’s Check Engine Light (CEL) will come on and stay lit. The reason it stays lit is to tell you something serious has happened. However, since you did not indicate whether the CEL is lit I am assuming it is not and therefore the only way you will know if a hard error code has been generated is by using the diagnostic probe. Once you have obtained any error codes that might have been generated, you can find the general areas that have to be repaired. Or, if you are lucky, the software has been updated to give you the exact areas that need to be checked.

In general, you will find that the OBD-II diagnostic information gives you a broad-brush global view of system problems. And, if no transmission-related error codes have been generated, you will have to have the transmission torn down and checked to find the exact problem. That’s not exactly an inexpensive proposition as the teardown and diagnostic work can take the better part of a day or more. At current mechanic’s rates — which do vary nationwide — and assuming a 10-hour diagnostic, you will be laying out nearly $1,500 just for this piece of the puzzle. Should you invest the money, at this point? If the Envoy is a special vehicle to you or you just want to stay out from under new-vehicle payments, then have the work done.

Assuming, though, that you want to keep the vehicle, at this point, it is likely a good idea to call local salvage yards looking for SUVs like yours with lower mileage and that have working transmissions. If you find one, pay the cost — likely about half of the cost of a rebuilt transmission — and have it poppoed in. If the new transmission is in good shape, then you should have few troubles later on.

If you choose not to go this route, then here are the problems that I think your transmission has. Notice that I said problems. They are likely:

1. The torque converter: When you noted that your transmission clunked it indicated to me that this device has a problem, possibly a bent vane or other damage (damage probably caused by some debris getting shaken loose and which then was sent through the fluid-filled device, causing damage to the converter).

2. The clutches: When you noted that your SUV had no reverse but did have three of its forward speeds, it indicated that the problem might also be in the clutch packs. It is possible that the clutch and band for reverse have failed, causing the problem. I am only suggesting this as a cause as second hasn’t failed. Usually second and reverse share many of the same components.

3. Valve body damage: It is possible that one or more of the runners in the valve body may have been damaged either by hitting a large bump or piece of debris in the roadway that may have shot up and into the transmission. Usually, the valve body doesn’t take hits like that because it is out of the way of most foreign bodies, but it is always possible that it may have.

4. Check-valve failure: Part of the valve body, check-valves open and close in response to fluid flowing through a specific set of channels. These channels define the gearing selection. If the fluid flow is blocked and the check-valves aren’t opening, then your transmission will behave as you indicate.

5. Gearing problems: When you noted in your description that your SUV has lost reverse and is only selecting three of the forward speeds, it naturally indicated to me that your transmission had gone into limp-home mode (I think this is the failure mode you are facing, but that’s beside the point right now, we are looking at possible causes), however, it is also possible that you have had problems with the gears and that reverse gear is gone. Just getting to reverse to replace it will require a major teardown and rebuild.

As you can see, then, there are a bunch of potential problems to deal with. Indeed, your transmission could even have one or more of the problems listed. What you are facing now is a decision. I will tell you honestly that your transmission is quite sick and that you should be thinking about replacing the entire unit. You can’t piecemeal a problem like this because you will end up paying more in the long-run if you attempt to fix it like this.

I know you are worried about price gouging, however, you don’t have to be as the most you will end up spending is about $3,800 to replace the transmission with a rebuilt unit. You can substantially cut that amount with the salvage yard unit so before you invest in a rebuilt transmission and have it put in, look for a transmission in a salvage yard. You’ll likely save about $1,500 on this unit.

There are, of course, a number of possibilit