HS PHEV - Hybrid Fault and complete shut down

[John WS]

HS PHEV - Hybrid Fault and complete shut down.
I have a late 2021 HS PHEV which has been dealer serviced from new, I have been watching this site since we got the car and have not seen anything like the issue we now have.
Last January (2024) the car coasted to a halt on the A30 on our return from Cornwall with a 'Hybrid Fault Warning', it lost all power and the systems shut down, the MG Assist/AA reset the faults and we continued for another 80 miles until the fault reappeared. We were then trailered home and arranged for the local MG dealers to fix it. It took a couple of weeks for MG to tell the dealers what parts to change (HV leak in the the HVAC pump) and the car was returned as fixed.
In March I replaced the original 12V battery as this suddenly refused to hold charge, a known problem.
Everything was then ok until our next drive to Cornwall in June (2024).
On our way back we got to the M25 and the 'Hybrid Fault Warning' came back and the car completely shut down. Got trailered home again and sent the car to the MG Dealer where it is serviced. They have had the car since June and have changed several parts under MG's guidance, even replaced the complete transmission/motor unit. They had thought they had fixed it several times but it has failed on the test drive each time, MG and the dealer are still looking for the fault.
Has anyone had a similar 'Hybrid Fault Warning' problem???
I will update when we do finally get the car fixed.

 

[Malcolm Evans]

On the 6th. October after shopping at our local tesco my MG HS PHEV refused to start, it then started (electric I believe) but 200 yards later stopped. Attempted to start it again but the noise sounded as though the gear box had disintegrated . Called Green Flag who trailered me across to local dealer Brindley MG in Cannock.
Diagnostic located faulty part which was took 5 days to reach Cannock. Three hours to fit and after ---- car would start in electric mode but would not then transfer to petrol.
STILL AWAITING FOR MG LONGBRIDGE TO COME UP WITH AN ANSWER.
Local dealer Brindley have helped all they can.
Have been told by Longbridge customer services department - that they will not discuss technical issues with me - as it is against the law. Also been told by them that I AM NOT TO CONTACT THEM FURTHER.
Now coming up to FOUR weeks with out MY car.

 

[John WS]

Malcolm, Sounds like a similar fault!! Our's can't be the only two tho'?
Our PHEV is still with the dealer who is now working with their SECOND MG Tech @ MG, they're still trying different fixes to get it going.
We didn't have any 'noises' or starting (EV or ICE selection) problems after the Hybrid fault appeared as it was completely non-startable, it would turn off and on from the START button on the dash but brought up 'many' fault lights on start-up but after a few seconds showed 'Hybrid Fault' then disconnected the HV battery and refused to do anything else but turn off.
A bit of investigation using the ZS OBD2 software showed a stored HV Insulation fault (HV to chassis leak), which makes sense of the originl fault when they changed the HVAC pump.
The MG PHEV trained Tech at the Dealer is very good and is trying hard to get a fix done. One thing he has said is that he is not allowed to dismantle or investigate any parts MG get him to change and they have to go back to MG for analysis, this prodcess does not help the dealers Techs get any experience in fault-finding tho'.
Last update was they are changing out some other parts and after another session on the rolling road they are going to try a long test drive. Fingers crossed we have a positive outcome soon.
The Dealer has been very good in loaning us their 2019 ZS runabout since our PHEV went in for repair and that has now done another trip to Cornwall and back, the 120 mile max range sucks tho'!

 

[John WS]

Another update, it's still broken!
The Long Test drive was ok on the way out but failed with a 'chistmas tree' of warning lights on the way back.
MG have now visited dealer to investigate themselves and the car is now going away to have the battery taken out and investigated internally by MG next week. Lets see what comes from that!

 

[John WS]

Whoop!! The car's back and running again !!!
Collected it from repair yesterday and we had a long chat with the technician who has been working on it since it went in for repair. He explained his job sheet and the repairs he had attempted under MG's instructions and also updated us on what was done when the battery was remotely investigated.
Parts replaced by the dealer; EDM, PEB, Transmission/TM (included another PEB), OBC.
It then went away for internal investigation of the battery and they changed the HV Relay unit, the HV/12V charger and lastly the HV BMS. Changing the HV BMS cleared the fault and it has not returned during their testing- P0AA6-00.
The fault was very intermittent when it went in for repair but became more repeatable as various parts were replaced and the car was recoded for the new parts.
The fault was narrowed down to the circumstance where - the vehicle had been driven for a while and then brought to a standstill, when pulling away from standstill (Auto or EV mode) the fault occurred and the HV battery disconnect happened (a safety protocol) = dead car.
They never found an actual HV leakage to the body but a faulty BMS/software fault that had triggered the shutdown.
As MG took back all of the original parts as they were replaced, we now have an almost completely replaced HV system including a new drive motor and transmission.
Hopefully this will be my last post on this particular problem!

It's just a shame it took so long for MG to diagnose and fix the problem (they did have four different MG technicians involved), this would have been a real issue for us if Apple MG had not been so generous with their supply of a courtesy car during the repair.
Thankyou Apple MG.

 

[AntC]

Well, that's interesting. I have a 2021 model bought second-hand from the dealer in Launceston, Tasmania. Mine has shut down twice, been trucked to the dealer's Service Centre and, once there and after a night's rest, the car started up OK. A mass of errors had been reported but (apparently) too many to help diagnose the problem - which had "gone away" anyway.

After the second tow to Service Centre (this time in Hobart) and another mechanic checkover after the car started up as if nothing had happened, again no problem was found. We were faced with a 200 kilometre journey back home. After 50-60 ks a set of fault messages appeared and then the car decided to limit itself to 90 kph. We kept going as everything sounded OK, all warnings were off and we simply had limited power. On a 110 kph highway we became a mobile chicane. I was not game to stop along the way while we were still moving and we made it home.

I left the car overnight and started it the next morning. All OK - System Ready. Full power was back and there has been no further trouble for 4 weeks and 350 kilometres.

With no fixed faults to diagnose the problem, my plan is to keep my fingers crossed every time I start it !! No, seriously, I'll get the 12V battery changed in the new year and see if that fixes the problems.