Dumb question re ACC

Technical Forum for the Porsche Macan
Paul1970
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Post by Paul1970 »

Have just started experimenting with ACC and wondering if anyone knows:

1. When it slows you down does it use the brakes because it feels like the slowdown comes from the engine reducing power, and
2. Do the brake lights come on?

The reason I ask is that I was on the motorway and there was a lorry behind me when someone pulled across in front of me and my car slowed down rapidly via the ACC. I was wondering whether the lorry behind got a warning via my brakes.
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Jon A
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Post by Jon A »

Paul1970 wrote: Tue Dec 21, 2021 9:49 am Have just started experimenting with ACC and wondering if anyone knows:

1. When it slows you down does it use the brakes because it feels like the slowdown comes from the engine reducing power, and
2. Do the brake lights come on?

The reason I ask is that I was on the motorway and there was a lorry behind me when someone pulled across in front of me and my car slowed down rapidly via the ACC. I was wondering whether the lorry behind got a warning via my brakes.
It will use either/or depending on deceleration required. The break lights do come on when breaks are applied (legal requirement) but be aware if you travel within a few miles of a large radar installation, the system will shut down. It will restart again when you are far enough away again but this is because of potential interference with both systems and presumably the government doesn’t want their expensive installations messed with! 😂
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On-Track
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Post by On-Track »

Paul1970 wrote: Tue Dec 21, 2021 9:49 am Have just started experimenting with ACC and wondering if anyone knows:

1. When it slows you down does it use the brakes because it feels like the slowdown comes from the engine reducing power, and
2. Do the brake lights come on?

The reason I ask is that I was on the motorway and there was a lorry behind me when someone pulled across in front of me and my car slowed down rapidly via the ACC. I was wondering whether the lorry behind got a warning via my brakes.
It will also use the brakes on downhill gradients to stop the car exceeding the selected speed. This is a step forward from the standard cruise control which just "pings" if you go over the set speed.

Unfortunately, ACC can react violently to cars pulling out in front. If driving normally and you spot a car acting in a way that indicates the driver is about to pull out you can "lift off" and create space. ACC carries on regardless until said car appears in front.
Peter

Current: 2020 Carmine Red GTS http://www.porsche-code.com/PMST9ZI9
Gone- 2015 Sapphire Blue Diesel
Gone -2013 Cayenne Diesel
Col Lamb
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Post by Col Lamb »

Anyone who is on a Mway or dual carriageway that has the ACC set may find it braking if you are a driver who changes lanes to overtake a bit too lane.

Conversely if some plonker overtakes you and cuts in too early or cuts out in front of you it will brake, the degree of braking is dependent upon how close they are and the setting of the distance control.

As you approach a vehicle you will feel the car braking but if you indicate and move to safely overtake braking will not occur.

With ACC turned on but nit set (greyed out) the automatic emergency braking system is active.
Col
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Neil1911
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Post by Neil1911 »

^^^ the above two and its strict adherence to the set space in front leads it to use the brakes far more than you would yourself and reduces their longevity. Had to have my rear pads replaced after 20k so I have modified how I use the ACC and take over myself if it looks to be lots of speed varation required, reverting to ACC when a greater cruise element returns, be that at 10 or 77 mph.
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Neil1911
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Post by Neil1911 »

Col Lamb wrote: Tue Dec 21, 2021 3:08 pm With ACC turned on but not set (greyed out) the automatic emergency braking system is active.
Col, have you actually experienced this working? Whenever, I've had it that way there's never been a hint of it doing anything, I'm not timid but my nerve always gives way before there's any sign of braking! In the manual I've only seen reference to the car adding brake pressure when the driver is already braking hard and a potential collision is detected. I've been considering a test with a cardboard box but not tried it yet :)
http://www.porsche-code.com/PP37WLA6, a Dolomite Silver S, collected from Stockport OPC on Valentine's Day 2023, after a 399 day wait.
Ex.: Gen2 S, Volcano grey 1/9/19 - 3/2/23 & 39,235 Smiles, RIP
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Post by Tracky »

Neil1911 wrote: Tue Dec 21, 2021 3:20 pm
Col Lamb wrote: Tue Dec 21, 2021 3:08 pm With ACC turned on but not set (greyed out) the automatic emergency braking system is active.
Col, have you actually experienced this working? Whenever, I've had it that way there's never been a hint of it doing anything, I'm not timid but my nerve always gives way before there's any sign of braking! In the manual I've only seen reference to the car adding brake pressure when the driver is already braking hard and a potential collision is detected. I've been considering a test with a cardboard box but not tried it yet :)
On our Seat (which is a cheap Porsche but has ACC as standard) the cruise does not need to be on for the autobraking to work - I know this as I hate ACC so much I never use it and yet it has emergency braked for us before now.
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Paul1970
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Post by Paul1970 »

Neil1911 wrote: Tue Dec 21, 2021 3:13 pm ^^^ the above two and its strict adherence to the set space in front leads it to use the brakes far more than you would yourself and reduces their longevity. Had to have my rear pads replaced after 20k so I have modified how I use the ACC and take over myself if it looks to be lots of speed varation required, reverting to ACC when a greater cruise element returns, be that at 10 or 77 mph.
After dipping my toes into the ACC world today I came to exactly the same conclusion in terms of using only when road conditions dictate that it should remain relatively steady driving. It's a bit nerve racking on a busy motorway when I would have eased off the gas in anticipation of someone pulling in front of me which would involve no use of brakes but the car had to quite forcefully drop from 75ish to 50 before then accelerating back up to speed because it couldn't anticipate the same as I can due to its "tunnel vision". Given the move towards self-driving I presume that the Tesla, for example, has a more intelligent ACC system because instead of relaxing the driving experience I was more on edge.

And also worth noting that the Lane Keep Assist wanted me to drive in the middle of a country road because it couldn't detect that there were 2 lanes rather than one. "Drive in the centre of the road" it kept warning me :o

Really enjoying getting to know the "safety systems"!
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PorscheMack
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Post by PorscheMack »

Paul1970 wrote: Tue Dec 21, 2021 4:01 pm
Neil1911 wrote: Tue Dec 21, 2021 3:13 pm ^^^ the above two and its strict adherence to the set space in front leads it to use the brakes far more than you would yourself and reduces their longevity. Had to have my rear pads replaced after 20k so I have modified how I use the ACC and take over myself if it looks to be lots of speed varation required, reverting to ACC when a greater cruise element returns, be that at 10 or 77 mph.
After dipping my toes into the ACC world today I came to exactly the same conclusion in terms of using only when road conditions dictate that it should remain relatively steady driving. It's a bit nerve racking on a busy motorway when I would have eased off the gas in anticipation of someone pulling in front of me which would involve no use of brakes but the car had to quite forcefully drop from 75ish to 50 before then accelerating back up to speed because it couldn't anticipate the same as I can due to its "tunnel vision". Given the move towards self-driving I presume that the Tesla, for example, has a more intelligent ACC system because instead of relaxing the driving experience I was more on edge.

And also worth noting that the Lane Keep Assist wanted me to drive in the middle of a country road because it couldn't detect that there were 2 lanes rather than one. "Drive in the centre of the road" it kept warning me :o

Really enjoying getting to know the "safety systems"!
Based on your thoughts would you spec it again?
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On-Track
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Post by On-Track »

Neil1911 wrote: Tue Dec 21, 2021 3:20 pm
Col Lamb wrote: Tue Dec 21, 2021 3:08 pm With ACC turned on but not set (greyed out) the automatic emergency braking system is active.
Col, have you actually experienced this working? Whenever, I've had it that way there's never been a hint of it doing anything, I'm not timid but my nerve always gives way before there's any sign of braking! In the manual I've only seen reference to the car adding brake pressure when the driver is already braking hard and a potential collision is detected. I've been considering a test with a cardboard box but not tried it yet :)
I have no idea if ACC changed between the Gen 1 Macan (which is what Col's Turbo is) and Gen 2 but in Gen 2 the EBA (Emergency Brake Assist) and AEB (Automatic Emergency Braking) are provided as part of PAS (Porsche Active Safety). Don't you just love all these TLAs (Three Letter Abbreviations) :lol:

PAS is present if you've specified ACC but apart from AEB using the same radar system as ACC is entirely separate. PAS is "on" by default, unless switched off via the PCM (Still keeping up with the TLAs? :D :D ). If AEB is activated because the car thinks there is a threat there is a loud series of pings and the MFD displays a flashing red warning. If you fail to brake then the car first of all pulses the brake system and, if the threat is still there applies the brakes. I've had it activate twice in 16 months and on both occasions the car thought the threat was greater than I did.

EBA activates if you rapidly move your foot from throttle to brake and press firmly on the latter. EBA then assumes an emergency and powers up the brake application to the maximum possible. It cuts out immediately if you ease the pressure on the brake pedal.
Peter

Current: 2020 Carmine Red GTS http://www.porsche-code.com/PMST9ZI9
Gone- 2015 Sapphire Blue Diesel
Gone -2013 Cayenne Diesel
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