I took our 2003 Toyota 4Runner to the dealer for four things:
Battery I would theorize.
I would have said battery but who knows. Assuming they used a memory minder, the battery shouldn’t have caused everything to go back to default. The important point is they fixed and even more miraculous it didn’t require a new appointment and the tech knew what to do.
You are all better mechanics than I am. It was the battery. My guess, when I took the car back was something had happened when changing out the brake fluid that caused a problem in the antilock brake system which is related to the traction control system.
I have used an inexpensive battery tender when I have had to disconnect a battery.
I have almost become paranoid about doing my own automotive repairs fearing that I will mess something up. It used to be that the only thing that would happen in disconnecting and reconnecting the battery is that the clock would stop. A friend called me because she had driven 25 miles into town and couldn’t start her Toyota Prius. I knew it had a little 12 volt battery as well as the main high voltage battery. I did try to jump the 12 volt battery in the Prius with no results. After 15 minutes, the Prius wouldn’t start and when I used my volt meter, the battery voltage was only 8.6. At that point, I was whipped. I reasoned that replacing the battery might not solve the problem as it should have charged up on the 25 mile trip to town and I was hesitant to take my friend to a place where she could buy a new battery. I convinced her to have the Prius towed to the Toyota dealer and take my van back to her house.
I did go home and read up on hybrid electrical systems. The problem in my friend’s car was the 12 volt battery. I really am embarrassed that I haven’t kept up on today’s technology.
If I had done the work on the 4Runner myself, I would have saved myself another problem. Our Toyota dealership always washes the car after doing service work. When we picked up the 4Runner it was clean and I was embarrassed as to how dirty our Sienna was. I took the Sienna to an automated car wash. The carwash wouldn’t accept my credit card, so I put in a $20 bill for a $10 carwash. I got my change–40 quarters. I had to gather up the quarters and put them in my hat.
When i still owned my 1977 Corolla I did most of my own maintenance with two exceptions: 1. There was a local tire shop that had a cheap price on oil changes so I took it there. 2. I never did my own brake work. A coworker who was a shade tree mechanic insisted that installing brake pads was a cinch but I told him I refused to drive a car with brakes I had installed. 
Nobody wants those things now. They tell me the casinos are open with the proper social distancing but they rarely take quarters now. And parking meters don’t use them now either. I used to keep a bag of them in the car for the meters but alas they use cards now. I did find a self serve car wash that still takes quarters and was able to get rid of some washing my lawn mower off, but if you need some more I’ll send a bag full. Bank doesn’t want them either. Maybe the grandkids will take them.
It’s like the late,great Groucho said " I wouldn’t be a member of any club that would have me as a member".
@Bing The self serve carwash I used does take quarters. The carwash will get them back when I go for another carwash.
What was their explanation? If the ABS controller had lost steering angle sensor calibration or yaw rate calibration during battery disconnect, the ABS and brake warning lights should also have been on.
If only the Trac Off light was on then I suspect that they pushed the Trac Off button a second time to switch it back on.
@Nevada_545 This was what was written in the service order:
“trac off lights come on once moving
Caused by
found zero point calibration needed
recalibration performed. all is working as designed”
There is no button on the selectable 4 wheel drive 2003 4Runner to turn off the traction control, although the 2 wheel drive 4Runner does have such a button. I checked this out in my owner’s manual.
The only thing the manual says for my four wheel drive version is to “see your dealer” if this warning light comes on.
The button to turn the traction control on and off was the first thing that came to mind as I do have an on/off button for the traction control on my front wheel drive 2017 Sienna. There is just a blank cover on the four wheel drive 4Runner that I own where the manual shows the trak off switch is on the 2 wheel drive 4Runner.
At any rate, the system works as it should. I did spin the tires purposely and the traction control activated when I got the 4Runner back.
You probably have a good start on a 50 State quarter collection, It will occupy your time and keep your car safe.
@oldtimer_11 I may use the quarters to go gambling. I don’t need to go to Las Vegas. I can travel two miles to the university campus where I taught for 44 years and play the vending machines. When I used to play the coffee vending machine, the odds were in the favour of the machine that the cup wouldn’t drop down and the coffee would go down the drain. When I played the machine that dispensed candy bars, often my selection would stick in the machine and I would get nothing. The next person who selected the same candy bar would then get two candy bars. One time during my 44 year tenure, I was the lucky winner and got two candy bars. Unfortunately, I didn’t quit playing the vending machines and ultimately lost many quarters.
Years ago, Mrs. Triedaq and I went to Las Vegas by Amtrak. It stopped at the Union Plaza hotel where we had reservations. While Mrs. Triedaq went to the powder room, I put a penny in the penny slot machine. I won 7¢ and didn’t gamble the rest of the trip. When I was a kid, I used to gamble on the gum ball machines. More often than not, I would put in my penny and the machine wouldn’t give me a gum ball but I would play the gum ball machines anyway. These were Ford gumballs.
If I was a rich man, I might try the autovend machines that dispense cars. My selection would probably stick in the machine and I wouldn’t get a car and the next purchaser would get two cars, but I might get lucky as I did the one time in my 44 year career when the vending machine dispensed two candy bars when I just paid for one.