This problem has really surfaced in the past few years with the 4T65E transmission and will catch you off guard for seemingly no reason.
Here's the scenario-
You are driving along just fine and no reason to suspect any problems. You make a stop at the gas station or grocery store and when get back to your vehicle you start the engine and put the shifter into Drive and nothing happens. Not believing that this is really happening you move the shifter between Park and Drive again and still nothing. If you have tried moving the shifter around more you will have found that the vehicle moves fine in Reverse and will also pull away in 2nd and 1st ranges.
If you have ran into this problem then you likely have a broken Forward Apply Band. I see more of this on the 00-02 model years but it does occur on other years as well. Unfortunately a broken forward apply band means a full rebuild to replace as it is one of the last parts to come out of the transmission case during teardown. There are numorous thoughts and opinions as to why this happens but there really isnt a definate answer, and being that this is more of a year related condition that makes it more difficult to track down the cause. High line pressure is going to be brutal on transmission parts, and I am not just referring to WOT driving conditions. Pressure problems in general in this transmission are going to cause trouble at some point in time. Code P1811 puts the transmission in max line pressure once it sets and can be another culprit and maybe why it is not found as often on the 03+models because there was a newer designed pressure control solenoid used that didnt have near as many problems as the earlier versions. Regardless the route cause of WHY the band broke, it is broken and needs to be replaced. Below are a few pictures of forward apply bands and how you can tell if yours has broken or not. One picture is of a good band, a fractured band that was on its way to failure, and a broken band. Sometimes you may find about a 1" piece of metal from the band laying in the lower transmission pan when you drop it for inspection. Other times the lug will tear on the band where it is brazed on.
The first picture below shows you where to inspect in the transmission case to identify the problem. This picture shows what a GOOD forward apply band looks like in regards to where the apply pin pushes on it
This next picture is the same view but the forward band is broken and missing the entire lug section that the apply pin pushes to engage it.
The next picture shows 3 different Forward Apply bands. From left to right you will see a band with a broken off and missing apply lug just as the above picture shows, next a fractured band, and to the right is a band in good condition.
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