OK to disconnect battery for a while? What cable?

[e9999]

I am planning to put in a battery disconnector, both to stop a runaway starter and also to provide some additional level of security when leaving the truck someplace unattended for long periods of time. I have to decide whether to disconnect the whole electrical circuit from the battery or just the starter. There are pros and cons to each security wise, but wanted to check the issue of computer memory etc.
I've read here that if you disconnect the battery for more than a few minutes you lose some memory storage, like the CEL codes etc. And probably also whatever fine tuning the computer has generated for your driving / gas conditions etc. I also remember reading that the ECU has charts stored so that it can go back to default settings after a power interruption.

So, how bad -or not- would it be if I were to disconnect the battery for several days, say, on a routine basis? No effect, rough engine afterwards, what?

And, there is no advantage to disconnecting the neg side instead of the +, right?

Also, I imagine that the big cable going to the battery serves only the starter while the smaller ones do everything else. That right? There is one thick cable plus one bundle with fusible link boxes (?) connected to the + post.

 

[Scamper]

So many questions...so little time

You have already enumerated the potential issues you'll see, except for one: if you've set a security code on your radio, you'll have to reset it each time you disconnect the battery.

Otherwise, I think you've covered the basics.

 

[e9999]

OK, more specific then:

- will the engine run rough or the mpg decrease if I disconnect the battery for a while?

 

[Junk]

e - every time I leave my rig at the airport etc I turn the marine switch to off. In my pos setup, the marine switch dictates which batt sends juice to the starter. Is it a fool proof theft plan? No, but it's another obstacle for them to deal with.

 

[elmariachi]

OK, more specific then:

- will the engine run rough or the mpg decrease if I disconnect the battery for a while?

Your truck has no way of knowing if you left the battery unhooked for 1 day or 30.

Seriously, the memory in your ECU is non-volatile, meaning the important programming stuff doesn't get erased by power termination. Otherwise, ECUs couldn't lay disconnected on the shelf in parts departments and Toyota's warehouse. Other than the radio security code, the only thing you will notice if you had your battery disconnected (regardless of 1 day or 30) is a high idle on startup, but that will go away in a matter of seconds.

p.s. It oughta be against Mud rules for BOTH moderators to be lurking in the same thread at the same time. This leaves thousands of unsupervised posters running amuck in other threads.

 

[e9999]

Your truck has no way of knowing if you left the battery unhooked for 1 day or 30.

Seriously, the memory in your ECU is non-volatile, meaning the important programming stuff doesn't get erased by power termination. Otherwise, ECUs couldn't lay disconnected on the shelf in parts departments and Toyota's warehouse. Other than the radio security code, the only thing you will notice if you had your battery disconnected (regardless of 1 day or 30) is a high idle on startup, but that will go away in a matter of seconds.

p.s. It oughta be against Mud rules for BOTH moderators to be lurking in the same thread at the same time. This leaves thousands of unsupervised posters running amuck in other threads.

a) that would depend on how long it takes for the volatile stuff to be lost
b) what about the info on timing etc per the octane rating being run, is that non-volatile also?
c) what's this high idle resulting from?
d) we can multitask (and the amoker, the better for us anyway... )

 

[Cruiserdrew]

OK, more specific then:

- will the engine run rough or the mpg decrease if I disconnect the battery for a while?

No-It takes 3 start stop cycles to relearn everything, but it runs fine on the default settings. You are worrying way too much again.

 

[Junk]

c - high idle is due to ecu resetting
d - speak for yourself. I can only do one thing at a time. Want to know what I'm about to do?

 

[e9999]

snip
d - speak for yourself. I can only do one thing at a time. Want to know what I'm about to do? %$#@^

Noooooooooooooooooooooooooooo!

 

[turbocruiser]

Maybe I missed it above but to answer one of the questions, always disconnect the negative cable first then the positive ( normally I dont disconnect the postive at all unless I have to like if I have to remove battery or wire or re-wire something). The reason for this is that if you slip some and touch a tool to the vehicle while you are on the negative terminal, nothing will happen cause you are already at ground. If however you ground between the positive and the vehicle you just created a hand held welder with yer wrench! HTH

 

[elmariachi]

a) that would depend on how long it takes for the volatile stuff to be lost
b) what about the info on timing etc per the octane rating being run, is that non-volatile also?
c) what's this high idle resulting from?

Some helpful reading on ECM and OBD2 and how they operate is at http://www.4x4wire.com/toyota/4Runner/tech/OBDII_ECU/:

Long Term Trim Long Term Trim is a learned value over time which changes gradually in response to conditions such as fuel oxygen content, engine wear, air leaks, variation in fuel pressure, altitude and so on. Long term trim is a component of what Toyota technical literature refers to as the "Basic Injection Duration". Basic Injection Duration data is stored in a nonvolatile RAM and is not erased even when the engine is shut down. This information is used during warm up and wide open throttle conditions.

Short Term Trim Short Term Trim is instantaneous correction value determined from the oxygen sensor readings. Under normal conditions it cycles rapidly around the 0 percent correction value and is only functional during closed loop operation. Short term trim is a component of the "Corrected Injection Duration". Corrected Injection Duration is used only during closed loop operation and not during open loop conditions. When Short Term trim exceeds plus or minus 10 percent for to\o long, the Long Term trim begins shifting, changing the Basic Injection Duration to bring the Short term trim back within the plus or minus 10 percent range. Short term trim can vary as much as plus or minus 20 percent, but the above correction mechanism works to keep it within plus or minus 10 percent.

 

[e9999]

Some helpful reading on ECM and OBD2 and how they operate is at http://www.4x4wire.com/toyota/4Runner/tech/OBDII_ECU/:

Long Term Trim Long Term Trim is a learned value over time which changes gradually in response to conditions such as fuel oxygen content, engine wear, air leaks, variation in fuel pressure, altitude and so on. Long term trim is a component of what Toyota technical literature refers to as the "Basic Injection Duration". Basic Injection Duration data is stored in a nonvolatile RAM and is not erased even when the engine is shut down. This information is used during warm up and wide open throttle conditions.

Short Term Trim Short Term Trim is instantaneous correction value determined from the oxygen sensor readings. Under normal conditions it cycles rapidly around the 0 percent correction value and is only functional during closed loop operation. Short term trim is a component of the "Corrected Injection Duration". Corrected Injection Duration is used only during closed loop operation and not during open loop conditions. When Short Term trim exceeds plus or minus 10 percent for to\o long, the Long Term trim begins shifting, changing the Basic Injection Duration to bring the Short term trim back within the plus or minus 10 percent range. Short term trim can vary as much as plus or minus 20 percent, but the above correction mechanism works to keep it within plus or minus 10 percent.

aaaaah! a good precise tech answer (to a vague question). Excellent. So, it seems like the info on gas etc is stored in non-volatile mem. So, disconnecting the battery should not affect the mpg then. Good to know.

 

[e9999]

Maybe I missed it above but to answer one of the questions, always disconnect the negative cable first then the positive ( normally I dont disconnect the postive at all unless I have to like if I have to remove battery or wire or re-wire something). The reason for this is that if you slip some and touch a tool to the vehicle while you are on the negative terminal, nothing will happen cause you are already at ground. If however you ground between the positive and the vehicle you just created a hand held welder with yer wrench! HTH

sorta makes sense.

you're not saying that I should put the disconnect switch on the - side, though, are ya?

 

[turbocruiser]

sorta makes sense.

you're not saying that I should put the disconnect switch on the - side, though, are ya?

No, I did not pay any attention at all to the disconnect switch part of the post, doh!!! I was answering what i thought the title asked, now that i read the real post, I can see I was answering a question you did not really ask, double doh!!! Pardon me for that, but still, to answer the title about if its okay to disconnect the bat, yes it is and AFAIK it makes no matter whether you disconnect it for 1 minute or 1 year, and to answer the title about which cable to disconnect, disconnect the negative for the reasons I listed above. Sorry for not paying attention, smack, to myself!!!

 

[elmariachi]

sorta makes sense.

you're not saying that I should put the disconnect switch on the - side, though, are ya?

I'm not sure it will matter, but I would do the + side. An interrupted negative is easily overcome with a jumper cable to ground. What would be real slick is to locate one of the switches with the removable key under the mish-mash behind the battery box. If you brought the cable out of the back of the battery box like normal and down to the hidden switch, you could really slow down a would-be thief.