High speed brake fail + ghost braking

[Deleted member 9277]

Hi all,

I've just seen some posts from @Bamboo and @RichRead about brake issues with their ZS EVs, thought I'd add our experience as well as this doesn't seem to be a small issue.

We've got a 2021 ZS EV bought in June from new. For the first 7 months the car was fine. We'd noticed that sometimes there would be a crunching sound coming from what we assumed was the emergency braking system, prepping in case of a crash however the brakes hadn't been affected.

However in March this year, we were leaving the motorway from 70 mph and started slowing down for the junction, but the car seemed to only be regen-ing as opposed to braking. As I realised we weren't slowing down enough, I fully stood on the brakes, body off the base of the seat and the car acted as though I wasn't even touching the brakes. ABS didn't kick in, we just narrowly avoided rear ending another car by a fingers width.

Naturally scared by this encounter, we turned off all of the safety assistance and then the car acted as normal for the remainder of our drive. I took it to our local MG authorised dealer and they couldn't find a fault with the car, said they'd done a software update to see if that would help.

We carried on using the car but fast forward three months and the same thing happened again as we approached a (fortunately empty) roundabout. We drifted into it as the car wasn't stopping. I then got the car to a safe place and tested emergency braking twice back to back and it worked fine, ABS kicked in as I would have expected.

So my concern is the brakes very intermittently don't work, which is what I assumed happened to the other two members of the community I mentioned. Were fortunate enough to have not hit anything whilst the car brakes aren't responding, but we're currently left in a position where we've got this car on finance, MG again can't find a fault and we just want rid of it as I'm genuinely concerned and don't feel safe driving it. I think there must just be a faulty batch of these cars.

I will mention as well, we've also experienced the main display completely crashing when driving and fading to black and all of the sensors from TPMS to lane assist and AEB saying they're "unavailable" when we've not touched anything. Also, I will say this is not that I've accidentally had my foot on the go pedal at the same time as on long drives I will drive barefoot so would have known I was on two pedals. I'm 100% certain I was not on both.

We also get the random emergency braking happen others have described. Can be a completely empty 3 lane road and it'll still happen.

I think MG need to properly investigate these cars but head office after sales just say "speak to the dealer" I've really not been impressed by how much they don't seem to willing to investigate more.

 

[TassieDi]

This sounds pretty scary. I'm about to take delivery of a 2022 model so I truly hope this is not a common problem!

 

[sgt4hed]

That is scary, I have experienced the noise of the brakes prepping in my 2022 MK2 but have not had a brake failure yet... What I would say though and this is probably telling granny to suck eggs, but DO NOT sell this car privately knowing that there is an intermittent braking fault. My advice would be to get a dashcam fitted and then use that to record the evidence if/when it happens again and give that to MG for them to sort it out. This is always the problem with faults, they have to be present for them to be diagnosed, if the fault isn't there when they have a look at it they can't tell you whats broken.

 

[Kithmo]

I've noticed a couple of times on a fast approach to a roundabout, the brakes don't seem to bite as much as I'd expect for the pedal pressure applied, it's as if the change from regen to hydraulic is a bit slow a bit more pressure on the pedal has always stopped me though.
The brakes have never actually failed on me so I put it down to a characteristic of the system and drive accordingly.
A fast press of the pedal, activating the EBA, bites straight away.
FWIW, SWMBO's MG5 brakes are much keener than my ZS's

 

[Coulomb]

I wonder if it could be a dodgy auxiliary battery, or something else in the 12 V system. That would explain the dash going crazy, as well as the lack of power assisted brakes (the 12 V system is needed to power the vacuum pump).

Some of these cars spent unknown periods of time sitting idle waiting for parts, who knows what happened to the lead-acid battery over that time. Of course, the DC-DC should keep the 12 V system at a good voltage once the car is "booted" (in ready mode), unless the battery has suffered something like one or more collapsed cells (a lead-acid 12 V battery is really six 2-volt cells in series). That might make it impossible for the DC-DC to keep the 12 V system running. But then I'd expect to have problems starting the car, more so than intermittently when the car is driving.

Or of course, the battery might be fine but the DC-DC is not working, which will quickly ruin the auxiliary battery as well, unless it's an intermittent fault. If the DC-DC is intermittent, that could explain the symptoms.

Some automotive technicians might not be thinking along these lines. An EV seems to be more reliant on a good auxiliary battery than the average ICE car. I wonder if some sort of "lemon law" could kick in here. I can understand you not wanting to use it. I think it needs to find its way to some nerd's garage, where they can tinker with it, and get a nice cheap, reliable car when they've eventually sussed it out and fixed it. But in the mean time, they have another vehicle to use.

 

[RamseyLewis]

In teslas if your brakes fails you can hold the parking button to stop the car. I wonder what will happen in mg evs.