System fault - stopped in a live lane of the motorway

[Mazzyh]

What a day!

Charged the car fully last night and set off for 100 mile round trip, which involved motorway about 40 miles. Traffic became stop start at one point, and without any warning. And that was it, the car is stuck in a live lane on the M4.

Recovery couldn't move the car initially, so I suggested disconnecting the battery and reconnecting it, at which point it worked. It worked. They drove it onto the lorry and then drove off the motorway and left me at the side of the road to the AA came.

The AA checked the car and the 12 volt battery was absolutely fine and they could find no faults at all. Fair play to the guy, because he said I will follow you all the way home but we won't go on the motorway. So we drove on the A4 back towards Reading and I got to a pedestrian crossing which went red, so I stopped and then the car wouldn't move again.

He then undid the battery and it gave me the ability to move the car which I drove for probably about another 200 yards and then the system fault appeared again. But this time as I was driving and the moment I stopped the car it wouldn't move.

After that I had to be recovered all the way to the dealership and no matter how many times you connected or disconnected the battery it wouldn't do anything, it just says system fault. We've had to leave the car there and it was closed by the time we got there.

It's been reliable up to now with no problems whatsoever so I don't know what's happened to it and he couldn't get any codes on his equipment.

I know people have had this happen to them before and disconnecting the battery seems to be the thing that solves it, but clearly that isn't working anymore and it just will not move full stop.

Obviously I'll hear from the dealership on Monday but I wonder if anybody's got any ideas what it could be?

Car is still showing 88% charged and the battery is at 13.8 volts going up to 14.1 when I'm driving.

It's not being a great day and to add insult to injury, unfortunately I smacked my head on a door that had swung back open and have managed to put a massive gash in my forehead. I think I'll go back to bed!

 

[salty]

WOW! Nightmare. Sorry to hear about that. Hope it's easily sort.

 

[Alb]

Worst time of the week for this to happen too.
Hope your dealer treats it as a priority.

 

[JohnV6]

Please keep us updated on this horror story

 

[Mazzyh]

It gets better ..not.

The dealership are not able to do anything with the car for about 6 weeks due to being down a couple of engineers and also bring fully booked. However they are very helpful and suggested I put a new battery in it. So armed with my voltmeter, I went to the car and tested the battery without anything on. It was 12.2v. I tried to connect my booster charger to it but it shuts off the boost after about 5 seconds, so I cannot close the bonnet and get into the car before it goes off. They think it all points to a failing battery - and it's still on the original 3.5 year old Saic battery.

So I'll do that. One query. AGM or stick to flooded? They said I don't need an AGM and I've read on here that the car is set up for flooded and AGM can therefore give the BCM bad readings (ie it thinks it's better than it is and so doesn't always recharge until it's really low). Any advice would be helpful.

However the big shock is MG has no record of any servicing being done on the car. It was an Enterprise Rental car (I confirmed with them today) and they use their own mechanics I believe. So getting any records will be difficult which means, if there is a major failure, the warranty is not valid unless I can prove it has been serviced to MG's schedule. All a bit worrying!

Again, advice would be welcome.

Apparently Enterprise by a huge number of these every year and then sell them off after they go over 3 years old - which is exactly what has happened here.

It's a bit of a fingernail biting moment!

 

[Everest]

You say the AA checked the 12V battery and found no faults - do you know if they just measured the open-circuit voltage or did they use some load test equipment on it (hopefully, the latter). If so, I'd say its unlikely to be the 12V battery, from the symptoms you've described. Having said that, maybe worth a punt if the alternative is to be without the vehicle for 6 weeks.

Regarding the warranty - did you not check the service history prior to purchase? Was it bought through an MG dealership or other dealer - if so, do you have written confirmation of service history or warranty status?

As you say, worrying time

 

[Mazzyh]

No, he basically attached some jumpers to it from a jumper pack which also tells him the voltage and he said it was fine, which I did think was a bit odd, but he may have had the car on in which case the DC DC converter would have been boosting the voltage. The fact that the actual battery itself is only at 12.2 volts, the dealership said is a major problem for the relays to shut, particularly the moment that he tries to release brakes or the heat is on or whatever electrical is running, and it gets a drain and it just can't do it.

As for service history, no, I didn't check because I presumed that nobody would be stupid enough to have a new car and not get it serviced. Although it will have been serviced. I just don't have a record of it because it will have been done through Enterprise's own servicing. Still it's not over yet, I'm going to try to get as much information as I can.

 

[Mazzyh]

Anyone have an opinion about the battery? AGM or flooded? Also, I've been quoted to versions: 027 (what I thought it was) and 075.

Thanks

 

[MickeySw]

The fact that the actual battery itself is only at 12.2 volts, the dealership said is a major problem for the relays to shut, particularly the moment that he tries to release brakes or the heat is on or whatever electrical is running, and it gets a drain and it just can't do it.

The 12V aux does not serve any purpose (all low voltage power is provided by the CCU) when the car is READY, you could actually remove it??

The fact that the car started just fine using the 12V aux means it's OK.

Disconnecting/reconnecting the aux does a full HW reset, which ‘fixed’ the underlying problem for a while??

I went to the car and tested the battery without anything on. It was 12.2v. I tried to connect my booster charger to it but it shuts off the boost after about 5 seconds, so I cannot close the bonnet and get into the car before it goes off. They think it all points to a failing battery - and it's still on the original 3.5 year old Saic battery.

12.2V is not great but OK (60% SoC). The booster shutting off either means the aux doesn’t ‘need boosting’ or a bad connection, ever tried to jumper it the old fashion way?

 

[Mazzyh]

It's a quirk of this jumper pack. It turns on and turns off. I've had it with totally flat batteries on my classic car and it just goes off after shoot 5 to 10 seconds. I didn't have an alternative.

I also get all the warnings about various systems not working, which is another sign of a low battery.

I've called another MG today to see if I can get a battery from them and confirm finally is this car is AGM or not. The original battery is still in the car and it's now 3.5 years old, so has probably survived longer than it should, according to what others say about the original battery.

Again, I'm only going in what I've been told by the AA guy (who was an EV only breakdown guy) who said he's seen this on lots of MG5s and hence why he then told me about most of them being Enterprise cars, which turned out to be correct about mine. Also the service department of MG where the car is told me the same thing too, it's just they have no capacity to look at it for 6 weeks.

From what I was told, the 12v needs to be above 12.4v in order for the contactor to close, otherwise once power to other systems kicks in, lights, brake etc, it puts a drain on the battery (also if it's weak this is even more pronounced) and the overall voltage drops well below the level to make the contactor work.

I guess I'll find out later today when I replace it. I'm hoping it sorts it else I'm then into the big money territory but without any warranty to rely upon.

Suggestions are DC to DC converter. The motor and main battery appear to be ok, and hence why I could drive until stopping.

I'll report later when I've managed to source the correct battery.