Disconnected battery=Computer Reflash?

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652
Location
RHODE ISLAND
When you disconnect the battery I've read that the computer has to "relearn" it's functions over a few days of driving and you can't take an emissions test, is what the computer goes through after a battery disconnect similar to "reflashing" the computer?
 
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1,904
Location
Canada
No. Flash EPROMs have persistent logic states, in other words, the programming survives removal of electricity. The configuration data that you are referring to, is stored in RAM in the ECU, typically. On a computer, this is colloquially* known as "CMOS" RAM. On most Intel x86 machines, this is accessed during boot-up by hitting a certain sequence of keystrokes. * colloquially, because actually CMOS is a type of semiconductor implementation process, with the characteristic of low power use, and use of FET transistors, as opposed to BJT's found in TTL logic. But "CMOS" is computer-slang for the type of low-power RAM that is installed to retain configuration settings, low-power, as in, it can be run for many years with merely the energy of a small battery. Unless you're an engineer, you really don't need to worry about specifically what CMOS is though :)
 
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4,036
Location
Chicago, IL
like pitzel said: nope - the important stuff is stored in static memory. I do have one truck that does lose its memory if the battery runs low.... but the same truck has no problem when I disconnect the battery for months at a time - so apparently the reduction in voltage affects it adversely. in fact, it forgets how to idle - I have to keep the rpms up myself for a few mins. silly dodge.
 
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1,904
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Canada
tomcat27, try cleaning out your idle air passages, and clean up your idle air control valve. The factory default 'trim' settings shouldn't have a problem keeping the engine idling at a reasonable speed, providing the passages are clean, and the IAC is in working order. Your issue might not be an ECU problem at all, but rather, the IAC having exceeded its maximum 'trim' setting in the ECU due to oil/dirt deposits. Especially with the IAC, designers are reluctant to design an algorithm in ECU firmware that just keeps opening the IAC wider and wider, because this could cause the vehicle to go into a momentary surge condition, and cause physical or property damage. Chances are, the ECU is just fine, and you've hit some sort of limiter. You could use a scan tool to verify IAC setting and trim.
 
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502
Location
Canada
It's referred to as volatile memory. Some (not all) engine related data is stored there. Other data can be stored in nonvolatile memory which remains after a power loss. Many new vehicles store DTC info in nonvolatile memory so that disconnection the battery won't clear codes. Re-flashing usually refers to reprogramming the modules EEPROM with updated info usually to fix problems. Kinda like a BIOS flash in a computer
 
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1,904
Location
Canada
Yeah Rabbler, early Flash EPROMs were only rated for a couple dozen cycles at the most. And in pre-mid-1990s ECU's, the EPROMS themselves were one-time-programmable or UV-erasable. Not modern Flash EPROM parts. Modern parts are rated for hundreds of thousands of cycles, so for the sake of simplicity and minimal design complexity, they may very well be storing 'trim' settings alongside factory microcode. On the same physical chip. BTW, the root cause of an IAC overlimit problem, tomcat, is overly frequent oil changes, which clog up the intake passages. Might want to consider that, especially if it gets cheap dino.
 
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19,479
Location
Chicago Area
After a battery cable removal, or other computer reset, E testing will fail you. A code will be in the computer to tell the E testing that it was recently reset. This is a safety so that someone does not reset a computer with many bad codes, and quickly drive to the E testing station. So it has to be driven a while, with up to 50 starts in some cases. Also, idle and fuel parameters are relearned . Use the AC also during various driving - there are parameters for that.
 
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2,431
Location
Toronto, Canada
 Originally Posted By: pitzel
BTW, the root cause of an IAC overlimit problem, tomcat, is overly frequent oil changes, which clog up the intake passages. Might want to consider that, especially if it gets cheap dino.
Never heard this one, is the reasoning that fresh oil has volatile components that vaporize early on after an oil change and then these vapors enter the intake thru the PCV?
 
Messages
35,994
Location
ME
The term you're looking for is "I/M readiness monitors" and the only way to know for sure is to check with a scan tool. There are lists around on google on how to do it, but you can get it done with 2 or 3 cold starts if you go through a full warm up and various, specific driving cycles. For me, "reflashing the computer" means going to the dealer and having it actually reprogrammed, like to cure an odd driveability thing they hadn't yet discovered at the factory. Another example is adding the factory cruise hardware from another car and needing to reflash the computer to let it know it now has cruise.
 
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19,479
Location
Chicago Area
Before you get a dealer reflash [even a free udpade], check online with others to see if the update hurts or helps. It can work both ways, for sure.
 
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5,532
Location
San Francisco Bay Area
 Originally Posted By: pitzel
Yeah Rabbler, early Flash EPROMs were only rated for a couple dozen cycles at the most. And in pre-mid-1990s ECU's, the EPROMS themselves were one-time-programmable or UV-erasable. Not modern Flash EPROM parts. Modern parts are rated for hundreds of thousands of cycles, so for the sake of simplicity and minimal design complexity, they may very well be storing 'trim' settings alongside factory microcode. On the same physical chip. BTW, the root cause of an IAC overlimit problem, tomcat, is overly frequent oil changes, which clog up the intake passages. Might want to consider that, especially if it gets cheap dino.
Electrical engineer here, so I actually understand these terms. I remember doing programming of UV erasable EPROMs with a quartz window for a UV eraser box. Once for my class project we were each given 10 PROMs donated by a manufacturer. These were programmed like standard UV erasable EPROMS in the same sizes, but with plastic packages instead of the ceramic packages typical with EPROMs. Then there were electrically eraseable (EEPROMs), then flash EEPROMs. And someone used the term "static memory" which probably shouldn't because it has a specific meaning in the electronics industry. Static memory (SRAM for example) is that which maintains its state without periodic refreshes. It tends to be faster than dynamic memory (DRAM), consumes less power when not switching, and and takes up more area per cell. It also loses the state of each memory cell when the power is no longer supplied. As someone else stated, the industry term is "non-volatile memory".
 
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11,247
Location
PA
One cold reset the Audi techs tought me is to just clap the battery terminals together (after being removed). This instantly discharges all the capacitators rather than meerely letting the car sit overnight disconnected. Not for the faint hearted. I do it all the time, on VW/Audis nd the Hondas too.
 
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10,597
Location
Nokesville, VA
 Originally Posted By: pitzel
Yeah Rabbler, early Flash EPROMs were only rated for a couple dozen cycles at the most. And in pre-mid-1990s ECU's, the EPROMS themselves were one-time-programmable or UV-erasable. Not modern Flash EPROM parts.
They may have even been mask-programmed ROMs. These are programmed by the layout of the mask used to make the chip, so in essence they are programmed when they are made.
 
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