I can't say specifically about Hondas, but I'll share as much as I know. Some really high-quality Chrysler radios are built by Mitsubishi and they will retain their station presets, but not the clock. Mitsubishi also makes radios for other car manufacturers. Honda is one that will not sell me radio service manuals, so I don't repair them for dealers, and I don't know who makes them. Regardless, there's no way it can keep the clock running when the battery is disconnected. As long as you don't mind resetting the radio, that's one less thing to worry about, unless it has an anti-theft code, which many Hondas do.
Fuel trim data, meaning "short-term fuel trims", (STFT) and "long-term fuel trims", (LTFT), tables will start to be rebuilt as soon as you start driving, without you even noticing. That applies to every computer-controlled fuel-injected engine. Where you can run into trouble is idle speed might be too low. You might have to hold the accelerator pedal down 1/4" for the engine to start and to stay running, and it may tend to stall at stop signs. Chryslers are famous for this. One parameter requires a very specific set of conditions for the Engine Computer to relearn when it must be in control of idle speed. The fix for that is uncommonly simple, but you have to know what to do. It simply requires driving and coasting for a few seconds.
Most programmable computers, especially by 2010 models, retain their customer preference settings. Things like speed-sensitive door locks activated or deactivated, computer chips in ignition keys, horn chirp when locking doors, etc., are usually remembered, otherwise you'd have to run back to the dealer all the time.
The place where most of the frustration stems from is the few manufacturers well-known to design in tricks to force you to take the vehicle back to the dealer to have numerous computers unlocked, and that can require a trip on a flat-bed truck. I hear about these horror stories all the time in training classes. The worst offenders are VW, BMW, and GM. The worst stories I've heard are about VWs. After reconnecting the battery, the engine may not start. If it does start, the engine will only idle when the accelerator pedal is pressed, and it won't come out of "park". The car has to be skidded off the hoist, out the door, and onto a truck for a trip to the dealer to have the computers unlocked. Their argument is if the car is stolen, those computers are worthless. My argument is the owner is more likely to be the one who is locked out of his car for simply replacing a bad battery.
Chrysler has always been the leading manufacturer in coming up with innovations that benefit car owners. GM has been the leader in dreaming up "customer-unfriendly" business practices that benefit GM. Needing to reprogram computers is one of their ways of getting you back to the dealership where your wallet gets sucked dry. BMW has their own tricks. It's bad enough when you know about these tricks and can plan for them, but way too many people get the unpleasant surprise at the most inopportune times.
GM started this with their "Delco-Lock" and "Theft-Lock" radios in the '90s, but you had to actually enter a code of your choice to activate the system that rendered a stolen radio useless. The good news is you didn't have to activate it. The bad news is if you had a stolen radio, all you had to do is visit any dealer's parts department and they would find the code you needed to enter to unlock the radio. It was just another way they could charge a fee.
In the '90s, a lot of VW radios also needed a code to be entered, but only the car owner knew that code. If he wasn't around, all you could do was throw that radio away. Real good planning on the part of the manufacturer.
A lot of Hondas need a code entered for the radio too. Start by looking in the glove box for a card with that code number. If you don't see that, ask at the dealer what the procedure is if the radio becomes locked. Chrysler only had a few models like that, and the dealer that sold the vehicle new has a record of that number in their files, but at the one I worked for, they were only required to keep those for seven years.
If I was working on a GM, VW, or BMW, I'd want to use a memory saver device and the battery charger together because if the memories are lost, I've heard of repair bills over $1100.00 to unlock the computers. Memory savers usually use nine-volt transistor batteries. Those can easily supply the 35 milliamps for the many memory circuits, but a single dome lamp draws close to half an amp, (500 milliamps). Accidentally opening a door could result in too much current for that battery to handle.
I've never had a problem yet with the battery charger, but be aware they do not put out a nice steady DC voltage. It pulses between 0 volts to as high as 18 volts. Keep it on the lowest charging rate to keep that maximum voltage at a safe level. Computers are very intolerant of unsteady voltage, and they will do weird things, but the low-current memory circuits have simple voltage regulators that can use the pulsing voltages. The main parts of the computers are turned off when the ignition switch is off.
There are also memory savers that plug into cigarette lighters but these also have their drawbacks. First, those outlets don't work in a good percentage of cars. The thermal safety cutout can be bad or the fuse can be blown. Also, it is real common to find those lighters only work when the ignition switch is on. If you see a plugged-in cell phone charger or some other accessory turn off when the ignition switch is turned off, those won't work with memory savers. You would have to leave the ignition switch on for them to be connected to the system. As soon as you disconnected the car's battery, the memory-saver battery would try to run all the computers. The nine-volt battery would sweat itself into a puddle!
There's one more clinker to be aware of that first showed up in the mid '90s. Many cars have Engine Computers that need up to 20 minutes to go to "sleep mode" after the ignition switch is turned off. This becomes a real headache when searching for a drain that kills a good battery overnight. These computers can draw up to three amps for that 20 minutes. The catch is if you do anything to interrupt that current, once reconnected, the 20-minute countdown starts all over and it draws three amps again. That interruption can be caused by lifting the battery cable off for a fraction of a second, or even just from rotating the range switch on a digital volt / amp meter.
What I would recommend is connecting your memory saver, keeping the doors closed and a window open, then waiting at least 20 minutes before you disconnect the negative battery cable. Once both cables are connected to the new battery, you can go about your business as usual, and you can remove the memory saver.
We have a dandy list of articles to check out. Click on "Repair Guides" on the top right of this page. specifically, you might find some useful information in this one:
https://www.2carpros.com/articles/how-to-replace-a-car-battery
Thursday, March 14th, 2019 AT 12:05 AM
