Hybrid C350 High Voltage Pyro Fuse Blown after reversing into a bollard.

[Shaun_Boland]

The vehicle in question is a C350 Hybrid reversed into a bollard, hitting the high voltage charging point. As a consequence, the seat belt tensioners activated, and the Pyro fuse was detonated in the High Voltage Battery pack. (No Airbags went off) There is a tennis ball size dent in the bumper

The Mercedes dealer has quoted £11k, and an authorised insurer repairer £15K. It is clear to me they are not taking any risks and the estimates are a bit short in detail of work

Question. Has anyone cracked open the HV Battery and replaced the Pyro Fuse?

I have 30 years plus of experience in electronic and electrical engineering, so it is well within my skill set, and I have an MB Star diagnostic, having taken a smart car apart.

The intention is to purchase the vehicle from the insurer and repair it.

Comments and advice, please.

 

[Craiglxviii]

Wear rubber gloves and best of luck to you!

 

[harrye500]

Me, I would be wanting to buy it from the insurers for very little ££ as I'd imagine the repairs will be complex but maybe with your experience you can get it back up and running!

 

[alexanderfoti]

There is quite a lot of "MB" specific stuff to get the HV system safe (xentry procedure and a small lead that needs to be be removed in the engine bay to peremantely de-engericse the contactor in the HV system.

Once the pack is out of the car, it can be split into lower voltage sections to make it safe(er) to work on. The biggest issues are:

1. Where to find a repalcement pyro fuse, as its likely a bespoke part for the battery back.
2. Whether the system writes a crash event into the BMS preventing it from being re-enabled, even after replacing the pyrofuse. This one may need some clever firmware modification or flashing.

 

[Shaun_Boland]

There is quite a lot of "MB" specific stuff to get the HV system safe (xentry procedure and a small lead that needs to be be removed in the engine bay to peremantely de-engericse the contactor in the HV system.

Once the pack is out of the car, it can be split into lower voltage sections to make it safe(er) to work on. The biggest issues are:

1. Where to find a repalcement pyro fuse, as its likely a bespoke part for the battery back.
2. Whether the system writes a crash event into the BMS preventing it from being re-enabled, even after replacing the pyrofuse. This one may need some clever firmware modification or flashing.

I think you have it about right. A get-out-of-jail card would be to buy a secondhand high voltage battery pack at a cost of £950 and swap the battery for the original know-good ones, or buy a know-good secondhand one at £3,000. However, if the battery pack is on the used market, it is likely to come from an accident-damaged car, and you are back to the same problem. If the BMS has an EPROM given time, I could reverse engineer it but would take a lot of time effort and testing

 

[alexanderfoti]

Yes exactly. Bms is likely vin locked as well.

Some ECUs are virtual eeprom so cannot be read/written to easily.

 

[Shaun_Boland]

Yes exactly. Bms is likely vin locked as well.

Some ECUs are virtual eeprom so cannot be read/written to easily.

Suspect, I am running into the right-to-repair territory. Had the same issue with VINs when I replace the ECU in a Smart Car

 

[alexanderfoti]

Suspect, I am running into the right-to-repair territory. Had the same issue with VINs when I replace the ECU in a Smart Car

Assume you are in the USA, in the UK We get bent over. No right to repair. We can bypass OEM implied "locks" in most cases, but some are hard (mostly key or drive authorisation related items that have encyrpted firmwares or require seed keys. )

 

[Shaun_Boland]

Assume you are in the USA, in the UK We get bent over. No right to repair. We can bypass OEM implied "locks" in most cases, but some are hard (mostly key or drive authorisation related items that have encyrpted firmwares or require seed keys. )

In the UK. You are saying the right words, "unfortunately". The insurance company has valued the car at £21k and wants £8k as a buyback, so need to start thinking if it is worth it

 

[alexanderfoti]

It is almost certainly fixable, you just need the right person.

If you cannot repair it, you can break it for more than £8k, but is it worth the risk/hastle?

 

[Shaun_Boland]

It is almost certainly fixable, you just need the right person.

If you cannot repair it, you can break it for more than £8k, but is it worth the risk/hastle?

Thank you for your help and input, it confirmed my suspicions. The info about swapping it out is very useful. Will keep you updated.

 

[harrye500]

This is a very interesting thread, early days in motoring terms for these sorts of complex and 'brave' repairs, will be genuinely interested in how you go in terms of feasibility and cost. If it can be done to reasonable cost then the car seems generally surely too good not to rescue. Will the insurer consider an offer on the 8k? Every £ saved would go towards repair of course so primarily all about gathering the known costs and then adding a bit of 'bunce' for unforeseens to your budget to conclude if it is justified?

 

[Nicklas_Hidegard]

Scary though to think that a small shunt from behind can write your car off..

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[Blobcat]

Scary though to think that a small shunt from behind can write your car off..

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Agreed.... they don't tell you that when you sign on the dotted line do they... anyone would think they don't wish you to know...

I'm sure it could all be recycled carefully by artisans and not just crushed and sent to the docks for melting down outside of the visible environment...