Battery Management System Reset

[Diocletian]

I had 'on brake idle hunt' and Lund tuned it out.

I've been fighting with them for 8+ months. They refuse to do anything more than raise my idle RPM which did nothing. First they blamed my O2 sensors, now it's my MAF readings that are going crazy.

I'm happy to report that after disconnecting my BMS that the problem went away, analyzing the logs shows the voltage is smooth as glass. I did not have any idle issues at all today.

They still state my MAF readings are wacky and told me to replace my filter...I am now on my THIRD air filter(had a K&N first, then aFe dry flow, now back to stock)

I have even gone ahead and cleaned my MAF as well, but I'm at the end of my rope for sure. For now, I'll leave the BMS disconnected as that is the only thing that made a difference.

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[Bahndvr]

I've been fighting with them for 8+ months. They refuse to do anything more than raise my idle RPM which did nothing. First they blamed my O2 sensors, now it's my MAF readings that are going crazy.

I'm happy to report that after disconnecting my BMS that the problem went away, analyzing the logs shows the voltage is smooth as glass. I did not have any idle issues at all today.

They still state my MAF readings are wacky and told me to replace my filter...I am now on my THIRD air filter(had a K&N first, then aFe dry flow, now back to stock)

I have even gone ahead and cleaned my MAF as well, but I'm at the end of my rope for sure. For now, I'll leave the BMS disconnected as that is the only thing that made a difference.

They were reluctant to retune mine but it was while I was stopped and foot on the brake.

Best of luck, hope you have it resolved and enjoy your ride.

 

[Diocletian]

They were reluctant to retune mine but it was while I was stopped and foot on the brake.

Best of luck, hope you have it resolved and enjoy your ride.

Yeah thats exactly when mine does it

 

[wireeater]

Bump. So I recently installed PMAS Cai and pbd e85 tune and I have the idle stumble as well. I checked all the connections and everything seems fine. The car drives perfect it's just idle. I was going to check the BMS as troubleshooting however I could not for the life of me find the second sensor. The one off the negative was easy. I used various posted images to try and locate it and non were correct to what I see. I have a 2019 Mustang GT. Can someone give me an idea. Is it possibly wrapped in tape on the harnesses.

 

[wireeater]

Nobody with a 19-20 unhook these sensors yet?

 

[Elp_jc]

So there are 2 BMS sensors??? I thought there was only one; the circle around the negative wire harness, right in front of the battery box. What's the second for? That's news to me. I just did the BMS reset because of battery replacement. Don't know if it was that, or simply the battery change that triggered all kinds of weird gremlins in my 2019 Bullitt, from the left mirror bouncing at the top adjustment, to the rearview mirror not having power (but windows do, which are on the same fuse), to the reverse bulb lighting up all the time (but not the reverse camera).

 

[GT Pony]

^^^ BMS reset not required depending on how the battery is charged, or how long the car sits undisturbed after a battery is connected or charged.

https://www.mustang6g.com/forums/threads/battery-management-system-reset.106897/page-6#post-2642693

 

[Elp_jc]

Supposedly it charges the battery less and less as it ages, and since I have FORScan, nothing to lose with resetting it, so did it right after changing the battery. But will read the thread you linked later on, out of curiosity. Thanks for the heads up, anyway.

 

[Bit_the_Bullitt]

So there are 2 BMS sensors??? I thought there was only one; the circle around the negative wire harness, right in front of the battery box. What's the second for? That's news to me. I just did the BMS reset because of battery replacement. Don't know if it was that, or simply the battery change that triggered all kinds of weird gremlins in my 2019 Bullitt, from the left mirror bouncing at the top adjustment, to the rearview mirror not having power (but windows do, which are on the same fuse), to the reverse bulb lighting up all the time (but not the reverse camera).

Hi Elp_jc, I remember you from other posts within the Bullitt comments, so I figured I'd drop in.
I have some weird electrical gremlins in my Bullitt now also. Have a dash cam that's hard wire via fuse tap, but should shut off at a certain voltage. I don't know if I have it set to cut off too high or what, but yesterday car wouldn't start after weird lights blinking, etc. Sat for 4 days without being driven.
Do you have any accessories etc in your car that it's doing these things?

 

[Elp_jc]

Hey, how is it going? Well, turns out I only had 1 gremlin, which was the mirror bouncing up after replacing the battery. Hasn't happened again. The other stuff was the reverse LED bulb not being CANbus compatible, AND that I wired the negative cable to the reverse ground, so when I turned the detector on, it didn't work, and was sending voltage to the LED, and since it didn't have resistors, it was partially lit. I have a new cable in the garage, but it's super hot still, so waiting until it gets cooler to install it. Also have located the appropriate ground, so everything should work out fine after that.

As far as your issue, at least you know what it was. I honestly would NEVER connect anything to constant power on a modern car brother, especially this Mustang, with such a marginal battery already. I'd relocate the fuse to a switched one, and buy a battery for that purpose (they sell them). Then you can connect that battery to the switched source, so it recharges when you're driving. That way you never have to worry about a depleted car battery anymore.

 

[Bit_the_Bullitt]

I get what you mean with modern cars. However, I had a 2018 Accord with manual, had a hard-wired kit for a StreetGuardian (similar to my current Viofo) dual cam setup and it worked flawlessly, never drained the battery.

So I think there's some issue with my current '19 Bullitt.
Due to quarantine I drive only about 1x/2x a week now. I drove on Wed or Thu, then tried to start the car on Sunday and it was completely dead.

I thought that it was the dash cam that was draining the battery. Unplugged it for the last couple of days, got a trickle charger and a portable jump starter (since wife drives a hybrid and can't jump with her car).
Even with the dash unplugged and the car sitting for barely over a day without being driven in a warm garage, the trickle charger said it was charging up from 35%!! I don't know how in the world it's gone down that low.
When I bought my car, it had a check engine light due to battery (CEL hasn't come back) and they put a new battery in. I wonder if these Ford Motocraft batteries are just junk?

How do you have your V1 done? I assume that's a radar detector...

 

[Elp_jc]

I have it connected to the mirror, but it's switched, so it only has power when ignition is on. I tried the correct ground and it worked, and reverse light stayed off, so I'm good. But will still replace the cable maybe tomorrow, so I can use the car again if needed.

As far as the battery, my car sat for months before I bought it, and my battery was toast too. Just didn't hold a charge for long. I thought it was the original battery, but it wasn't. When I replaced it with an AGM from Advanced Auto, I was expecting to see a July or August 2019 date, but it was March 2020, so 2 months old by the time I bought the car. The problem is dealers don't charge them, so they sulfate in that time, and since they're so marginal, you need a new one. Check the date sticker on yours; it might have been an old battery, even though it was new to you. If your alternator is putting around 13.5 volts, it is fine, meaning the issue is the battery. I recommend you get an AGM, like I did. They're better than flooded cells, and much safer, so the difference in price is well worth it IMO. I could have gotten a free replacement, but didn't want the same junk again.

 

[Bit_the_Bullitt]

I have it connected to the mirror, but it's switched, so it only has power when ignition is on. I tried the correct ground and it worked, and reverse light stayed off, so I'm good. But will still replace the cable maybe tomorrow, so I can use the car again if needed.

As far as the battery, my car sat for months before I bought it, and my battery was toast too. Just didn't hold a charge for long. I thought it was the original battery, but it wasn't. When I replaced it with an AGM from Advanced Auto, I was expecting to see a July or August 2019 date, but it was March 2020, so 2 months old by the time I bought the car. The problem is dealers don't charge them, so they sulfate in that time, and since they're so marginal, you need a new one. Check the date sticker on yours; it might have been an old battery, even though it was new to you. If your alternator is putting around 13.5 volts, it is fine, meaning the issue is the battery. I recommend you get an AGM, like I did. They're better than flooded cells, and much safer, so the difference in price is well worth it IMO. I could have gotten a free replacement, but didn't want the same junk again.

I think I'm going to have to go with the route of the switched-only, I'm hoping the hard-wire kit (that's made for switching between switched/acc and constant-on fuse) is capable of running just accessory, would really not like to run another wire.

 

[19 RKT PONY]

Good Info just reset mine w/ ForScan

 

[Elp_jc]

My battery is getting drained an inordinate amount after just a few days. Don't remember that being the case before (at least not that fast), and it's not the battery, since it's new. It wasn't as fresh as I wanted it, since it had an AUG '20 sticker (rather than Sep), and I bought it Sep 26, but it shouldn't be bad (it had 12.52V). And it's an AGM (DieHard). And fully charged it before installing it. And everything is off. After 3 days installed, it had 12.48, so it discharged more in my car in 3 days, than almost 2 months by itself.

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