The only thing that can be done with computer memories is to erase anything they've learned. That puts them back to the initial state they left the assembly line in. From then on, the computer updates with every shift cycle it goes through. In the case of the original computer-controlled transmission developed by Chrysler for 1989 models, it immediately learns the volume of fluid it takes to apply each clutch pack. Those volumes, called the "clutch volume index", (CVI), updates as the fiber clutch plates wear. That ensures the clutches are applied sooner before the previous one was released, to maintain the nice crisp shifts it had when it was new. The downside is we no longer get the two or three years of sloppy or mushy shifts that told us a rebuild was in the near future. Now we go from a solid shift yesterday to defaulting to limp mode today, with no warning.
All other manufacturers now have their own version of Chrysler's computer-controlled transmission. If you want to "reset" a computer thinking that is going to solve some problem, all you have to do is disconnect the negative battery cable for half a minute. Once you start driving again, the relearning will take it right back to where it was, usually within two to three miles or a half dozen shift cycles. Disconnecting the battery will also erase any stored diagnostic fault codes. That is the last thing you want to do. Those codes provide information on where to start the diagnosis. You don't want to lose that valuable information until after those codes have been read and recorded. After that, the codes can be erased, but that doesn't make the problem go away.
Sometimes diagnostic fault codes are set by accident when we're unplugging things while the ignition switch is on. When we suspect that might have happened, it is customary to record the codes, erase them, then drive the vehicle to see which codes come back.
Also be aware, related to those fault codes, there is always a real long list of requirements that must be met for a code to set. One of those requirements is certain other codes can't already be set. For that reason, it is often necessary to diagnose and repair the current problem, then the computer's self-tests will resume. That is where a different, new problem might be detected. That sets a new fault code, and we have to start all over with a new diagnosis. This gets to be very frustrating for car owners and mechanics. You think the first problem wasn't diagnosed correctly or repaired correctly. We had no way of knowing a second problem existed, and we really don't like having to tell you more work is needed than we originally knew about.
As for the dealer telling you they "reset" something, that's likely because that's what car owners expect to hear. You want to be told something was done that will solve a problem. Disconnecting the battery, or wiping the learned data with a scanner, will put the computer back to its original state, but that doesn't make other problems go away. Much of this thinking goes back to the late '80s to mid '90s when GM had a huge problem with Engine Computers. Sometimes they could be unlocked by disconnecting the battery, so today, that's what we remember, and incorrectly think it applies to all computers on all car models.
You didn't say what kind of problem you were having or how it was resolved. Understand too there are often software updates provided by the manufacturer to address common issues. While that's usually a good thing, I have known people at dealerships who look on that as an embarrassment and don't want to admit they updated a computer. Instead, they make up a line to keep us happy, such as "we reset something." My reply would be why did something need to be reset?
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Friday, July 22nd, 2022 AT 3:57 PM
