Hey, I brought my car (1998 BMW 328i - Automatic) in for an oil change, and also to have them look at my battery, heres the story.
day 1, battery died because I left lights on, had it jumped, ran the car for 2miles, was on for maybe 15mins, shut car off.
day 2, went to start car, battery died again. jumped car, brought to mechanic to look at battery and to do the oil change.
day 3. no one touched car.
day 4. mechanic when to drive car into shop to do the oil change, car wouldn't start. he charged the battery to full, did the oil change. everything looked good.
day 4.5. I went to go pick it up a few hours after he fixed it. (he said he disconnected the battery and he charged it to full and everything looks good) I started the car, started up no problem at all. But when I was going to shift it from P - R - N - D, it felt a little different, it kind of felt like the gears weren't shifting correctly because I could feel the back end of my car going down and up when shifting gears. not very bad but I said ok..... so I drove it about 15mins back to my location, while parked I decided to look a little more into it. I put it from park back into N, then from N to drive. I felt the car kind of bouncing lightly (just the body going up and down when shifting) the RPMs started to kind of go up and down also when shifting from the N to D. RPMs were steady around 0.6 when I had the car idling in park. when I was doing this shifting the RPMS jumped pretty weird. they would go from 0.6 to 1.2 then down to 0.3 then up to 0.7 then sit around there moving very little. it did this every time I went from N to D. I let it sit in D for about 1min just idling (foot on break) and then the RPMs went crazy, 0.6 to 1.2 down to 0.3 down to 0.1 up to 1.2 then it went to 0.1 and died. car shut off. all electronics still on (radio, lights, dash lights). I started the car back up, and the RPMs stopped going crazy, they were pretty steady back to normal, I couldn't reenact what I did before. everything just seemed to be fixed? I have no idea what was happening, I tried to get it to do it again for about 3-4mins but it wouldn't, the RPMs wouldn't go crazy it just seemed to have fixed itself.
In the mean time I told my mechanic about this and he said that I may need to "relearn the battery" because he had it unplugged for a little bit.
Heres what he told me.
1. Keep car in N for 1min and let it idle.
2. Shift into drive for 1min and let it idle (foot on break)
3. Accelerate only using 20%-50% throttle until the car auto changes gears to the highest gear.
4. Cruse in the car only using "light to medium" throttle for 1min.
5. Come to a light stop and allow the car to down shift automatically until its fully stopped.
He says this will fix the ECU and the battery.
Is this anything I should be worried about, Could this whole situation after the battery be related to this Re-learning of the battery, or do you think this guy was wrong.
whenever a battery is disconnected, the fuel trim parameters and shift parameters are reset to 'default' values. depending on how the engeneers designed the mapping, your actual 'defaults' may vary as the vehicle accumulates mileage. regardless, your vehicle will have to go through a resetting to fine tune the fuel trim. this may take more or less time depending on how and where you drive, the condition of the vehicle, and your sensitivity to the vehicle. (trust me, i have been in vehicles that felt like they had square wheels and the driver never even noticed it)
you should be fine, though. and it isn't the 'battery' that needs to relearn, (they're pretty stupid, really), it's the dme and trans module.
I dont understand why the car keeps dieing. Also that mechanic sounds like a tool himself. Is he half retarded? One thing for sure is dont go back there. If he told you that a car needed to "relearn" a battery and you didn't tell him hes a jack@$$ when he said it, then he thinks you know nothing about cars. Chances are he will tell you next time the blinker reservoir was broken and leaked all the blinker fluid out. If your alternator is messed up and surging on and off that could be an issue also. Check your battery with a multimeter and then start and check the voltage. You should have 13.5+ when running.
well, really, it's a little know secret outside of the auto technician world that when blinker fluid leaks out that it causes the battery to forget what it knows...true story...
seriously though, there is a 'relearn' process whenever the battery voltage (be it from a low battery or improperly charging alternator) drops too low, the powertrain control module will start back at a preset 'square one' when the voltage is returned. this is where erratic idles, shutters, stalls, and goofy driveability gremlins can come from when dealing with a battery replacement or jumpstart from leaving lights on. the good news is that most of these will smooth themselves out as the vehicle is driven and the parameters are adapted for the current driving conditions. if they persist, then i would suspect a charging system malfunction.
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