Uncommanded Parking Brake activation after a stop?

[Wallyo]

I will say every time I manually activate parking brake it releases itself when I hit the accelerator. Seems yours isn't doing that?

I will try that tomorrow.
I hardly ever apply the parking brake, we are in the flat of the valley So at home I never put it on. The area it happened in is in the Foot Hills.

I know my daughter's Bronco does that but she has a manual!

The thing here is I am not some guy complaining about a rattle, or a buzz when the Ac is on this is a major safety issue.

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[CLT-PB]

How

Just asking because although I do NOT enable auto-Hold, but rather use the steering wheel controls to initiate a brake-hold at a traffic stop, I have experienced the emergency brake being engaged if a brake-hold request results in a long enough hold time.

In other words, if the truck is being brake-held by the PCM, rather than my foot on the brake pedal, after a certain elapsed time the truck will apply the electric parking brake and notify me on the instrument cluster.

Do you think that "elapsed time" might be a participant in your scenario?

How do you use the steering wheel controls to initiate a brake hold? Never heard of that.

 

[Snakebitten]

How


How do you use the steering wheel controls to initiate a brake hold? Never heard of that.

If you are behind another vehicle at a stop, you can hit the set+ or set- button on the steering wheel. It will set cruise control to 15mph and then after a couple of seconds, sets the brake-hold. You can release your foot from the brake.

Once the train passes or the light turns green, you can either press the throttle or hit the resume button and the vehicle will release the brake hold.

However, as mentioned earlier, if the train lasts too long, the pcm will set the emergency brake and release the brake-hold. I never measured the time, but I have had it happen at trains a few times.

 

[KTM753]

However, as mentioned earlier, if the train lasts too long, the pcm will set the emergency brake and release the brake-hold. I never measured the time, but I have had it happen at trains a few times.

I didn't know this but it makes sense why it switches. There is no vacuum brake booster on our trucks, it's electric assist and a long enough draw will bring the battery down too much. Probably why it switches to parking brake application.

I wonder if the original posters issues have anything too do with low battery SOC... I wonder if the brake hold switch to parking brake is not a time limit but a battery SOC or low voltage limit?

 

[Snakebitten]

I honestly don't know. But with a Powerboost there is no 12V battery drain at a stop. No belt driven alternator necessary.

 

[Rinn69]

I didn't know this but it makes sense why it switches. There is no vacuum brake booster on our trucks, it's electric assist and a long enough draw will bring the battery down too much. Probably why it switches to parking brake application.

I wonder if the original posters issues have anything too do with low battery SOC... I wonder if the brake hold switch to parking brake is not a time limit but a battery SOC or low voltage limit?

Ah, look.....another example of the "sucks the sweat off a dead man's balls" BMS system....can't even keep a fairly important (sarcasm) system working... AS/S and the BMS system needs some serious overhauling, and soon !!!
At least I know now, that when my 24 arrives, I need to turn off the auto hold feature

 

[SilverPigeon]

A number of things (I never use auto-hold because sometimes I need to creep forward and stop, creep forward and stop etc. to get the front close to an obstacle. With auto-hold, the amount of accelerator needed to overcome auto-hold will travel the truck too much for my needs.):

1. For those experiencing the problem, disable auto-hold and see if the issue ever appears again. If it doesn't, it's auto-hold software/logic getting confusticated at times. Could be interaction with wheel speed sensors or a number of other interactions.

2. I don't see how this could possibly related to battery or SOC, because, from the reported descriptions, the engine is running at the time of the event. At this time, surely the alternator is providing as much current as required and a steady 14.7 / 14.8 volts. Check the voltage at the + battery terminal and chassis ground and also + and - battery terminals. This should eliminate BMS as an issue.

3. It's vital to check for any DTCs (in this thread, dealers have not reported to customers any DTCs found, or those with the issue have not mentioned any).

4. Report all instances of the event to the safety authority (NHTSA?) in your country to get it on record.

 

[KTM753]

2. I don't see how this could possibly related to battery or SOC, because, from the reported descriptions, the engine is running at the time of the event. At this time, surely the alternator is providing as much current as required and a steady 14.7 / 14.8 volts. Check the voltage at the + battery terminal and chassis ground and also + and - battery terminals. This should eliminate BMS as an issue.

If that was the case, there wouldn't be tons of battery related issues threads all over the place here and other spots. If the alternator can't charge a battery to full SOC over the course of a 5 or 10 minute commute done repeatedly, why would it in a brake hold scenario like a train crossing?

The brake booster and power steering on these truck is electric versus hydraulic on the previous generation. They both have very high current draw. Additionally the transmission pump during auto start/stop can draw 35 amps on its own. Combine all 3 at this train crossing example and I venture to guess the alternator isn't keeping up with battery draw. I could be wrong but looking at the system it's plausible...

Additionally if its not a battery draw issue the electric brake booster doesn't have a 100% duty cycle rating. It's meant to be used intermittently and give the system time to reject heat generated during operation. So auto hold hits a duty cycle limit and times out the booster, forcing the PCM to switch to parking brake. Also plausible.

 

[SilverPigeon]

If that was the case, there wouldn't be tons of battery related issues threads all over the place here and other spots. If the alternator can't charge a battery to full SOC over the course of a 5 or 10 minute commute done repeatedly, why would it in a brake hold scenario like a train crossing?

My point is that the engine is running at the time of these events. Unless the battery has completely failed (in which case the truck won't start) it should still have enough capacity to pass-through any required current/voltage demands. Also, unless changed with FORScan, the BMS won't allow a charge to 100% SOC anyway. So I can't see it as being relevant to the events.

The brake booster and power steering on these truck is electric versus hydraulic on the previous generation. They both have very high current draw. Additionally the transmission pump during auto start/stop can draw 35 amps on its own. Combine all 3 at this train crossing example and I venture to guess the alternator isn't keeping up with battery draw. I could be wrong but looking at the system it's plausible...

I agree that this is possible but again, even with a crappy H6, if it can still start the truck, it will most likely be good enough to supply needs while the engine is running

Additionally if its not a battery draw issue the electric brake booster doesn't have a 100% duty cycle rating. It's meant to be used intermittently and give the system time to reject heat generated during operation. So auto hold hits a duty cycle limit and times out the booster, forcing the PCM to switch to parking brake. Also plausible.

But all of these events are infrequent, to the level of someone who would use their parking brake even twice a day

 

[Snakebitten]

The shortcomings and influences of a low SOC 12V battery, at least on a Powerboost, don't really apply while the truck is energized. (Ready Mode)
Note: Even in Accessory Mode, a low SOC 12V battery isn't being taxed, since the DC/DC converter is engaged.

Yellow markup is showing the HV battery being taxed for 1.8 amps by the DC/DC converter
The DC/DC converter converts that to 42 AMPs of low voltage current, of which 3 amps is excess charging current for the AGM (green)

Even if the BMS isn't supplying adequate battery charging current, the current demands of the truck itself are being met by the DC/DC converter.

Below:
This is what you see if you turn the truck off but you haven't opened the door. The DC/DC converter shuts down, so anything/everything still on in the truck is depending solely on the AGM 12V battery.

Notice it can only provide 12.6V now, without the assistance of the DC/DC converter Yellow (Powerboost alternator).
And the AGM current is now a negative integer of 19 amps. Green

 

[SilverPigeon]

In addition, for non-PBs, if a battery were functional but FLAT, and the truck was jump started, all systems get their required power needs once the engine runs, so there's that

 

[KTM753]

In addition, for non-PBs, if a battery were functional but FLAT, and the truck was jump started, all systems get their required power needs once the engine runs, so there's that

But they don't... hence all the battery threads... look at the BMS video by Fordtechmakeuloco. His own 2021 F-150 has a 5% SOC just from his own short commute. Add in very high current draw events in this brake hold scenario and the alternator isn't keeping up. Most likely why the PCM applies the parking brake and removes the brake booster application.

 

[SilverPigeon]

But they don't... hence all the battery threads... look at the BMS video by Fordtechmakeuloco. His own 2021 F-150 has a 5% SOC just from his own short commute. Add in very high current draw events in this brake hold scenario and the alternator isn't keeping up. Most likely why the PCM applies the parking brake and removes the brake booster application.

Apologies; I mustn't be explaining myself well. I don't know what else to say except that I'm not talking about batteries themselves, but that as the events are happening while the engine is running, and the truck stays running after the event, the alternator must be keeping up with power demands. If this were not true, the truck would be exhibiting the event much more frequently, and the truck would also be experiencing many more electrical issues while driving, or stalling completely

EDIT: I've seen the video. His vehicle starts and runs for his trips. The alternator is keeping up with the demands of the running truck. The alternator/BMS strategy is NOT keeping up with charging the battery to the desired SOC I agree. But that is irrelevant to the case here as the truck is running.

It will be interesting to see what the final rectification of these events turns out to be.

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