# New car battery: how long till the computer is good on a Subaru

**URL:** <https://boards.straightdope.com/t/new-car-battery-how-long-till-the-computer-is-good-on-a-subaru/750575>\
**Category:** Factual Questions\
**Created:** [March 29, 2016, 10:01pm UTC](https://boards.straightdope.com/t/new-car-battery-how-long-till-the-computer-is-good-on-a-subaru/750575 "2016-03-29T22:01:57Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![salinqmind](https://avatars.discourse-cdn.com/v4/letter/s/3ec8ea/32.png) [@salinqmind](https://boards.straightdope.com/u/salinqmind)\
**Post date:** [March 29, 2016, 10:01pm UTC](https://boards.straightdope.com/t/new-car-battery-how-long-till-the-computer-is-good-on-a-subaru/750575/1 "2016-03-29T22:01:57Z")

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I have 2 more days to get my 2011 Subaru inspected. This morning 8 a.m. I found the battery was dead dead dead. Called AAA and got a new battery put in, called the garage. He said I have to drive it around a few days (!) so the computer will turn on and gather information, it won’t pass inspection till then. Well, I’ll be dipped. I never knew about this.

So just drive around for a while? How long? How fast? I’ve read complicated formulas for stop and go driving (I really don’t do highways - I can go 50 MPH after morning traffic for a few minutes down the road.)

Son of a beeyotch.

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**Author:** ![westhou](https://avatars.discourse-cdn.com/v4/letter/w/f1d935/32.png) [@westhou](https://boards.straightdope.com/u/westhou)\
**Post date:** [March 29, 2016, 10:22pm UTC](https://boards.straightdope.com/t/new-car-battery-how-long-till-the-computer-is-good-on-a-subaru/750575/2 "2016-03-29T22:22:27Z")

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GM says about 100 miles

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**Author:** ![core](https://avatars.discourse-cdn.com/v4/letter/c/d26b3c/32.png) [@core](https://boards.straightdope.com/u/core)\
**Post date:** [March 29, 2016, 10:25pm UTC](https://boards.straightdope.com/t/new-car-battery-how-long-till-the-computer-is-good-on-a-subaru/750575/3 "2016-03-29T22:25:21Z")

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You will need a cheap OBD II scan tool to see when the emissions status changes to ‘ready’. Unless you just want to pray and go to the inspection. I’m not sure I understand “I really don’t do highways”. You don’t have anywhere near you with a speed limit that high?

Here’s what Subaru apparently says about getting the readiness set in the shortest time (lifted from another site, can’t vouch for accuracy):

> [@](#):
>
> 1. Make sure the fuel tank is between one-quarter and three-quarters full; half a tank is ideal.
> 
> 2. Start the engine and immediately drive the vehicle for at least 15 minutes at a speed greater than 50 mph. During the warmup, try to avoid sudden acceleration, hard braking and/or lane changes.
> 
> 3. Drive the vehicle at a steady 55 mph for three more minutes. During this stage of the drive cycle, it’s crucial that you keep throttle angle changes to a minimum.
> 
> 4. Bring the vehicle hack to the shop, hook up the scan tool and look at the status of the readiness monitors. Repeat the drive cycle, if necessary.

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**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\
**Post date:** [March 29, 2016, 10:57pm UTC](https://boards.straightdope.com/t/new-car-battery-how-long-till-the-computer-is-good-on-a-subaru/750575/4 "2016-03-29T22:57:57Z")

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> [@core](#):
>
> I’m not sure I understand “I really don’t do highways”. You don’t have anywhere near you with a speed limit that high?

My mother drove for 50 years, and never went over 25. Some people wouldn’t know how to get on/off a highway, or how to drive on one. Good thing they stay off.