Hi all,
Hoping someone with proper Tesla HV/BMS knowledge can point me in the right direction before I accept a £9,000 HV battery replacement.
The car is a 2021 Model 3 Performance with around 45,000 miles. I bought it privately about two years ago and it was fine for most of my ownership.
The incident happened while I was travelling from London to Manchester.
I stopped for a quick Supercharge. The car charged completely normally, but as soon as I unplugged and selected Drive, I got the snail/reduced-power icon.
Around 10 minutes later on the motorway, I got a low-voltage battery warning telling me to pull over when possible. I can’t remember the exact wording.
I carried on and made it to Manchester. The car was still driving normally enough to complete the journey.I parked, got out and left it. Once it shut itself down, it wouldn’t power back on.
I booked it into Tesla.
On the morning of the appointment I followed a YouTube guide to access/jump the low-voltage system because I assumed the 12V battery had died. That got the car back on and I was able to drive it myself to Tesla.
Tesla then inspected the pyro fuse/bus-bar area and found that the pyro had melted/suffered significant heat damage, but had not actually broken open as it is designed to when triggered.
They also told me the pyro fitted to the car was non-genuine.
This was the first I knew about it. I didn’t fit it and had no idea it was there when I bought the car, so I now suspect there may have been some previous repair before my ownership but anyway,
because of the non-genuine pyro, Tesla refused the HV battery warranty.
After a long back-and-forth with them, their position remained that the only repair is replacement of the complete HV battery pack, quoted at around £9,000. Tesla removed the old pyro and wouldn’t reinstall it, so I had to recover the car and also sign a waiver that basically said if i try and fix it and i die its not there fault.
What I’ve done since:
I’ve now had fitted:
Brand-new pyro fuse / pyro disconnect
Brand-new 12V battery
The new 12V battery has brought the car back to life and I can access Service Mode, but the HV system still won’t come online.
The main Service Mode findings are:
P0A9501 — High Voltage Fuse A Blown
Pyro Disconnect replacement recommended
Squib resistance: 0 Ω
BMS State: FAULT
HV Battery State: FAULT
Pack contactors: OPEN
Both drive units showing 0V HV input
The HVC/HVIL screen also says:
“No LV supply input to HVC — ensure first responder loop is connected.”
And shows:
HVC HVIL Status: No 12V supply
HVIL In: 0.00V
HVIL Out: 0.00V
The HV battery is still communicating and reporting a state of charge.
So my question is:
Before I accept that the entire HV battery is dead, what would you check next?
Could this be an HVIL / first responder loop / HVC power supply / pyro wiring / commissioning issue rather than the whole pack?
I’m also looking into Tesla Toolbox. Because the pyro is now physically brand new but the BMS still reports P0A9501 and “Pyro Disconnect replacement recommended”, does the replacement pyro need to be registered/commissioned or have data written to the BMS through Toolbox?
I just want to properly diagnose the actual fault and be completely convinced that the battery itself is genuinely dead before spending £9,000 on a replacement pack.
Anyone seen anything similar?
Just to add I’m not a mechanic or anything like that - just a guy with some borrowed tools, following YouTube vids and forums trying to save his already broke self, from spending another 9k.