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Imagine that you diagnose a transmission failure in a 2004 Mitsubishi Galant
For the Mitsubishi Galant Fortis, see Mitsubishi Lancer.

The Mitsubishi Galant is an automobile manufactured by Mitsubishi Motors since 1969. The name was derived from the French galant, meaning "chivalrous".
. The customer authorizes the work, so you remove the box and send it to the most reputable automatic trans specialist in your area. Later, you carefully install the rebuilt trans and erase the existing trouble codes with your scan tool. (To cover your bets, you had removed the PCM (1) See phase change memory.

(2) (Plug Compatible Manufacturer) An organization that makes a computer or electronic device that is compatible with an existing machine.
 fuse and left it out while the trans was away in order to clear the computers learned values.)

Although you're feeling very confident about this job's outcome, the road test turns ugly. The Galant This article is about the musical style. For the Mitsubishi automobile, see Mitsubishi Galant.
In music, Galant was a term referring to a style, principally occurring in the third quarter of the 18th century, which featured a return to classical simplicity
 shifts terribly; the transmission performs so badly that you're convinced you either damaged a connection or left something unhooked during the installation. But you don't find any obvious mistakes when you double-check your work. To add insult to injury, the PCM has reset the same trouble codes that you already cleared! Perhaps The Great Technician in the sky is punishing you for some past transgression.

Unfortunately, this job taught you a tough lesson about something called nonvolatile memory See non-volatile memory. . In short, this is a situation where you have to command the PCM to erase its existing learned values and start over from scratch. The only way to issue this command is with the appropriate scan tool. A predicament like this poer-srufting Galant could cost an unsuspecting technician dearly, so pay attention here.

First of all, I'm not a computer whiz and many of you reading this column probably aren't, either. At the risk of oversimplify- ing, I'll be as brief and basic as possible. Let's start by relating it to a common personal computer or laptop. An itty-bitty battery inside the computer maintains memory containing vital pieces of data about the computer's characteristics and operation. If the battery ever failed, your computer would revert back to certain default settings and values. In the process, for instance, it would forget the correct date and time as well as such things as the number and types of drives inside that computer.

A capacitor is similar to a battery in that it stores energy. Traditionally, automotive computers such as an ECM (1) (Enterprise Change Management) See version control and configuration management.

(2) (Error Correcting Mode) A Group 3 fax capability that can test for errors within a row of pixels and request retransmission.
, PCM or TCM (1) (Trellis-Coded Modulation/Viterbi Decoding) A technique that adds forward error correction to a modulation scheme by adding an additional bit to each baud. TCM is used with QAM modulation, for example.  have relied on capacitors to maintain vital bits of memory such as learned driving characteristics-often called adaptive or learned operating values. If battery power for that computer is lost for any reason, the capacitor does its best to maintain the adaptive learning (algorithm) adaptive learning - (Or "Hebbian learning") Learning where a system programs itself by adjusting weights or strengths until it produces the desired output.  memory. Over the years, you may have noticed that if you work quickly, you can replace a car's battery (without using backup power An additional power source that can be used in the event of power failure. See UPS and backup.

A Half Minute of Backup
This roomful of lead acid batteries stands ready to drain itself entirely in less than a minute.
 or a memory saver of any kind) with no ill effects on engine and trans performance.

On the other hand, some of us have seen a vehicle run poorly after its battery was left disconnected for a fairly long time. But simply driving this vehicle restored normal operation by allowing its ECM, PCM or TCM to relearn Verb 1. relearn - learn something again, as after having forgotten or neglected it; "After the accident, he could not walk for months and had to relearn how to walk down stairs"  its adaptive operating values.

Sometimes these computers do a remarkable job of keeping the vehicle running in spite of some failed components or sensors. But the obvious drawback to this capability is the fact that the learned values end up skewed skewed

curve of a usually unimodal distribution with one tail drawn out more than the other and the median will lie above or below the mean.

skewed Epidemiology adjective Referring to an asymmetrical distribution of a population or of data
 far in one direction or another. For instance, just look how far a failing mass airflow Mass airflow may refer to:
  • Mass Airflow Meter
  • MAFless Tuning

macrophage activating factor.
) sensor can push long-term fuel trim!

Anyway, we want the affected computer to relearn normal operating values as quickly and seamlessly as possible after a repair. After all, the customer just shelled out money for us to make the car run like new again, right? He may not be eager or willing to tolerate any "break-in" behavior.

Consequently, some technicians hasten the relearning re·learn·ing
The process of regaining a skill or ability that has been partially or entirely lost.

re·learn v.
 process by erasing a computer's existing adaptive memory. Sometimes, pulling the computer's fuse and leaving it out while you repair the vehicle does the trick. Other times, the tried-and-true way to erase adaptive learning is to disconnect the battery cables and touch them together for a minute or so. When you short the battery cables together, you ground out that capaci- tor, draining off the voltage that maintains adaptive memory. This is the fastest, most effective adaptive memory-erasing trick for some computers. Obviously, the downside is that disconnecting the battery clears out memory of other components.

Now let's return to the seemingly goofy Galant I described earlier. It has a PCM, so one module is controlling both the engine and trans. Since approximately 2004, Mitsubishi has been updating its vehicles to PCMs fitted with nonvolatile memory. At the very least, our sources said, this changeover has occurred every time a vehicle line is updated to CAN bus capability. So the Galant received CAN bus and nonvolatile memory in 2004, the Eclipse got them in 2006, the Outlander in 2007 and the Lancer in 2008. However, the nonvolatile adaptive learning memory also appears on some Mitsu vehicles that don't have CAN.

As I already explained, you can't erase this nonvolatile memory by pulling a PCM fuse, disconnecting the battery and/or shorting the battery cables together. Instead, you need a scan tool that's capable of commanding a learned value reset. We know that the Mitsubishi OEM (Original Equipment Manufacturer) The rebranding of equipment and selling it. The term initially referred to the company that made the products (the "original" manufacturer), but eventually became widely used to refer to the organization that buys the products and  scanner shown in the photo on page 12 performs this function. If your scan tool cannot do it, then you'll have to budget the time and dollars to have the local Mitsubishi dealer reset the learned values for you.

Mitsubishi specialists emphasize that you should perform the learned value reset after you repair the engine, trans or their control systems. You should also do it after erasing DTCs or reprogramming Reprogramming refers to erasure and remodeling of epigenetic marks, such as DNA methylation, during mammalian development[1]. After fertilization some cells of the newly formed embryo migrate to the germinal ridge and will eventually become the germ cells  a PCM. They explain that unless you reset (essentially, zero out) the existing adaptive values, the PCM continues using them after you've repaired the vehicle. For instance, this could cause a new trans to shift very harshly or allow engine rpm to flare during shifts. Equally distressing is the fact that the existing adaptive values can cause those codes you cleared to recur during your road test.

So how much, if any, latitude do you have with this reset requirement? Thus far, it appears there's precious little latitude here when the PCM has made sizeable changes in learned values. For now, we recommend searching for reset capability in a scan tool. If the proper equipment is not available, budget the time and bucks to have the local Mitsu dealer perform this memory reset before you return the vehicle to your customer.

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Author:Dan Marinucci
Date:Dec 1, 2008
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