Customers with complaints of not shifting, wrong gear starts, late or early shifts are considered to have shift timings issues.
For an automatic transmission to shift, there are two things that need to be known: 1) How fast the vehicle is moving. 2) How hard the operator is depressing the accelerator.
Sorting out the source of the issue can be complex. The first step in finding the truth is to separate the command to function from the transmission ability to function. The “Command” observation centers on the vehicle speed vs throttle position state. The simplest way to do this is with a scanner that reads, codes, and provides observable data. We observe the Power Train Control Module command a shift while watching the transmission’s ability to make the shift.
If a command to shift isn’t occurring we diagnose it as a problem outside of the transmission. If the command to shift occurs but the transmission doesn’t change speeds, we conclude that the problem is with the transmission.
Whether the problem is inside or outside the transmission, there are possibly minor or serious problems.
This writing is not intended to accurately diagnose a problem. Rather, it is to give the reader some insight into the complexity of diagnosing modern vehicles and instill some confidence that our processes will serve people needing this type of service.