Unexpected Power Surge

Faults and Technical chat for the Volvo XC40
wilkia2
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Joined: Mon Nov 30, 2020 12:10 pm

Post by wilkia2 »

While parking my automatic petrol XC40 yesterday, the car suddenly surged forward, as if I had hit the accelerator instead of the brake. While I am sure it is possible to press the accelerator instead of the brake, I don't think its possible to do it and not realise afterwards. So that's a mystery.

Maybe it's possible accidentally to resume Cruise Control by brushing the button on the steering wheel with your sleeve whilst turning to park. But the Cruise Control hadn't been used on that journey.

There is also the question of why the automatic braking system didn't cut in.

The car hit a grass bank and dented the passenger side front bumper. Impact speed was slow, no seatbelt burn (and certainly no air bag deployment). Damage looked superfical, so I drove home.

On the way home, the radiator fan started running and it subsequently turned out that the coolant had all leaked away. There was no other sign of a problem, certainly no coolant warnings. When I did check the coolant, I also discovered that it drained away within a minute of being topped up. So not a slow leak.

This morning, I started the car (but not the engine) and there is now a coolant warning.

Car will be collected later today and looked at by the garage.

All in all an odd and worrying episode.
* why the sudden power surge?
* why no auto braking?
* why no coolant warning?

wilkia2
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Joined: Mon Nov 30, 2020 12:10 pm

Post by wilkia2 »

Well, it has happened again, but this time no damage was done. The circumstance was similar, driving from chalk/gravel onto grass in a car park. I am thinking that the change of surface caused the traction control to privde additional power, although this is exactly the wrong thing to do under these circumstances.
Deleted User 3359

Post by Deleted User 3359 »

CC won't resume or work at low speeds (<20mph???)
blastpipe
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Post by blastpipe »

Sure it's not the autobrake releasing and jumping you forward...and you adding extra revs?
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Greggspies
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Post by Greggspies »

Is it possible that you caught the side of the accelerator pedal with your shoe while your foot was on the brake? It could happen without you feeling it.
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Chris John
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Post by Chris John »

Turn auto brake off…..
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wilkia2
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Post by wilkia2 »

Cruise control wasn't on, but even so adaptive cruise control does work a low speeds (for example in queueing traffic).

Could be autobraking, but there were no obstacles about on the second occasion, which why I suspect traction control. On the first occasion, there was a grassy bank to hit and collision avoidance braking did not prevent me hitting it. Garage said the bank would have been too low to trigger it.

I am as sure as I can be that it is not accidental pressing of the accelerator.
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Greggspies
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Post by Greggspies »

Traction control reduces power or applies selective braking - the opposite of what you experienced.
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wilkia2
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Post by wilkia2 »

Hmm. In that case I am out of ideas.
blastpipe
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Post by blastpipe »

I'd bet it is the auto parking brake applying..then releasing when you pressed the accelerator to move forward again. In tight manoeuvres you are much better off releasing the parking brake manually if it has autoactivated before pressing the accelerator..gently. Otherwise what you have described can happen - I know as I've got close to hitting something. Nothing to do with cruise control.
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