UKC

Evening all

My son in law bought a second hand car from a private garage about a month ago.

After a week it broke down. He tried to jump start it with leads to no avail so the AA were called who couldn’t start it.

They called the garage owner who graciously came out and collected it and offered them a lift home.

The next day he phoned and said it was electrical and had my son in law tried to jump start it, which he admitted he had.

A week ago the car was returned with a new CPU and battery and a bill for £200( half of the cost to repair apparently) which they paid.

All well and good until yesterday when it wouldn’t start again.

Theyve spoken to the garage owner and asked for a full refund to which he’s replied ‘it’s not that simple due to the overload that happened when you jump started it.’

Given that he can’t prove that the attempted jump start caused the issue as the car was already broken down, how would you approach getting a refund and any legal proceedings if necessary?

The car has an AA approved sticker on it, would this be an avenue to pursue?

thansk a lot

Dave

Jump starting needs to be carried out using the correct sequence otherwise damage to the electronics is fairly guarenteed on any vehicle less than 20? years old.

Ideally your son in law would know the correct method and be able to convince the garage that he had so done .

I believe the dealer is on the hook for up to six months, ie the dealer will have to prove the fault was not pre existing at the time of sale which of course is tricky to do.  The ECU issue muddies the waters but since replacing it didn't fix the car, that sounds like a red herring. So my understanding is the dealer is obliged to give a refund, less any charges for depreciation/usage. I get the impression that dealers are not keen to go to court as the law does not look on them favourably, so stand your ground in spite of any initial bluster.

Easy for me to say, I know.

If the car worked fine after they replaced the ECU then either jump starting it did no damage, or any damage caused was fixed by replacing the ECU.

He can't claim that the jump start has had some long lasting intermittent damage. Cars are jump started all the time. That car may well have been Juno started multiple times before you bought it.

It worked fine when it was last fixed so the jump start is water under the bridge at this point.

Sounds like he put the leads on the wrong way around and fried the ECU. Seems the garage repaired it at a very reasonable price so I don’t think you’re in buy back territory there. 
what’s the reason for the current non start?

Sadly my experience suggests that it is not as simple as that.

Many modern cars have multiple ECUs handling different electrical systems and an incorrect jump start procedure can easily damage more than one of them.

Putting the leads on the wrong way round (i.e. connecting positive to negative and vice versa) would produce such a massive spark and make the cables very quickly get very hot - nobody could do that and not notice.

(I know you're meant to connect negative to bodywork rather than the negative battery terminal, but I was always of the understanding that that was to protect the battery rather than anything to do with not frying the ECU).

I wondered this, but would it still spark if it was a completely dead battery? never tried so no idea.

I could see there being a battery drain issue that was the original fault.

Maybe the jump start blew the ECU, but usually, I'd expect to blow a power train fuse and not an ECU.

But let's say ECU blew, replaced, all good, but you've still got the parasitic drain issue. If that's the case warranty should be honoured.

These kinds of threads can be a bit of a pain, as you so often get descriptions like "it broke down". What does that means, was it a crank no start, just ticking, any electrical life at all?

It sounds like it ran for a week with no issue. Had an issue occurred with another ECU at the time of the jump surely this would have been immediately obvious after the first offending ECU was replaced.

My gut is telling me it's a dodgy alternator regulator or similar that's causing spikes and blowing things. It really wouldn't surprise me if an ECU was replaced as a trial and error before realising it was a fuse or relay.

It is almost impossibel to tell without knowing what the full symptoms are or access to the fault codes/live datastreams from the vehicle.

I have got away with non-textbook jumpstarts many times and would have assumed that it was unlikely to be the jumpstart that caused the problem if I hadn't got involved in the long and painful process of diagnosing a whole string of faults caused by regular poor jumpstarting on someone elses car last year.

Some cars appear to be great when it comes to isolating and protecting the different electrical systems from our incompetence, others can be an absolute nightmare in this respect.

It happens a lot, and is more likely to cause ECU or injector damage than not applying loads to the system. I don’t know if the person noticed it or not, just my opinion on the most likely cause. 
Yes, that is the correct way I believe, with electrical loads switched on so as not to cause a spike. 
I have personally never had an issue jump starting and feel you’d have to do something very wrong to cause issues like that

Same, although my Lexus hybrid specifically says not to jump start.

It doesn't have an alternator and instead uses DC-DC to charge, so not sure if it's to protect the charger from a high demand that it can't regulate.

Or may it can't handle noisy alternator electric.

Either way, I reckon you could jump start it with the other car switched off with no issue. Maybe. 

Even then I'm often still left scratching my head with electrical issues.

using same key?

A spike in what?

Short of connecting the leads the wrong way round I'm struggling to see how you damage anything. I can see things reporting low/unstable supply fault codes but I doubt that would result in worse than a check engine light.

jk 

Obviously not the case here, but the only other thing that can go wrong is a spark lighting gas from a battery. Pretty rare.

Most of the "rules" around jump starting are to avoid an accidental ignition or accidently dropping the positive cable on the chassis.

I always connect directly +ve and -ve to terminals on both ends. Connect the dead battery first, then the jumper battery. I find my clips are less likely to ping off compared with finding some unpainted lump of metal. 

All this about needed to most direct -ve connection is just nonsense (assuming you don't have a bad earth). 

Saying this, all bets are off on newer stuff that has a BMS. I've not learnt yet what you can and can't do with them.

I agree, and the only time I’ve come across an isssue is when the leads have been connected the wrong way around. 
 

in terms of a spike, the line at Ford was that you’re suddenly introducing around 15v to electrical components designed to run on 12v. As I say, never had an issue jump starting a vehicle. 

It's increasingly common for modern cars to be fragile and behave in what appears to be badly designed ways (perhaps it's intentional design?) but simple things like jump starts, disconnecting and reconnecting the battery incorrectly can damage a growing number of modern cars, this is "progress"

The modules are clearly all designed to run at the elevated charging voltage rather than the nominal. The difference in inrush current will be neither here nor there to devices capable of surviving the rigors of normal operation and the utter chaos of an actual start.

Playing devil's advocate to my sceptical side, I suppose the inductance of the leads and the arcing as you make connections to a dead battery will result in some nasty high voltage fast transients but again, this is expected, understood and accounted for by regulation/design. And a working car will do just the same as you open and close the starter solenoid.

jk

i've just had to do most of this to replace a battery! (didn't trust halfords

youtube.com/watch?v=zJin9McPkLE&

I used our Transporter to jump start my tractor and something happened which damaged the abs module, I had to replace it, the leads were connected properly, the garage said it must have been a surge as the tractor started, if I have to jump start now I make sure I have the lights and heater blower on so there is already a draw on the alternator, it could be because the vehicle has a smart alternator maybe. 

You may be right in terms of the jump start and it not being possible to spike an ECU, like I say it’s not something I’ve experienced and I only know what I’ve been taught by manufacturers in that respect. Maybe it’s a myth. 
 

I wouldn’t assume though that everything is designed to run at a higher voltage, because it’s not. 

It really is.

Everything connected to the vehicle's '12V' supply (almost always simply the battery in an ICV and typically more like 13V than 12 at rest) has to be able to withstand operation at the normal charging voltage, so around 15V for a 6cell lead-acid, plus some overhead so the input filters aren't dissipating significantly in normal operation.

Plus of course surviving/rejecting any fast transients one could reasonably expect on that supply. The compliance tests for this are brutal!

jk

You can believe that if you like, but it’s not true

Weird. 12V tractor, right?

jk

Specifically which bit is not true?

There is simply no way anyone would design for 12V maximum operation knowing it would be connected to a basically unregulated supply that swings between <10 and >15V in normal service.

jk

not everything on a car is unregulated voltage and not everything is designed to withstand battery voltage as not everything is supplied directly by the battery. 
All makes and models are different with varying levels of technology. 
i get your opinion, there’s clearly a lot of knowledge behind it and maybe we are at cross purposes. 
 

Is the tractor running an alternator? If so, wonder if it's faulty. Could explain why it needed jumping in the first place. If it's throwing out high voltage spikes, other than shortening the life of your battery it may well go unnoticed on an old tractor (assuming it is an old tractor).

Yes but I was quite specifically talking about equipment that is connected directly to the battery derived nominal 12V supply.

jk

Thanks John

He and a friend bought a new set of leads and having never jumpstarted a car, they read the clear instructions on the box, so it is incorrect for some, including the seller, to conclude that he did it incorrectly causing damage. The AA man also tried to jump start it and the seller asked if HE had done it correctly.

It sounds like the seller is clutching at straws  

The car has started today and he is going to drive it back and ask politely for a refund or start legal proceedings.

thanks

Dave

Jkarran is right. You can't damage electrics/electronics in a car by jump starting it.

Anything that needs protecting or regulating will be protected and regulated.

And everything is supplied from the battery and/or alternator. Where else do you think the electricity is coming from?

The reason you are supposed to earth to the chassis when jumpstarting in newer cars is so as not to bypass the BMS that is in the battery negative. Connect clamp to chassis, chasis connects to battery negative via BMS. If you connect directly to battery negative the BMS don't see that current going into the battery.

But how would you know? Unless your fully up to date with all makes and models. 
An ECU might expect a 12v wake up signal at key on, engine off. What happens if there’s already 15v there on a part of the system that was never designed to see operating voltage. 
I’m just speculating there I don’t know the answer 

What did the car need to start today? Any idea what was wrong with it?

Yes it is running an alternator, pretty sure there is nothing wrong with it as it was about 8 years ago and everything has been fine with the tractor since then, I think the battery was low before I fitted it to the tractor  and yes it's old, 1983 Ford 1210.

I never suggested he was wrong although I do think it’s interesting and would like a more definitive answer. 
 

just like jkarran, you are incorrect about power supply if you are suggesting that everything runs on 12v directly from the battery. 

there maybe not much wrong with it. you need to describe the fault in more detail. eg a friend couldn't start her car (engine turning but no start) because her key fob had fallen apart and she didn't put back the chip..

You are barking up the wrong tree.

Everything runs from the battery or alternator. There is no other source of electricity on a car. There is no magic electricity trees floating in the air waiting to be used.

The voltage coming off them isn't constant and will vary between 10.5v (flat battery) and 14.5v (alternator powered up coupled with a full battery). There is not such a thing as a 12v battery pushing 12v. In fact a lead acid battery has a safe useable range of 12v to 12.7v with 12.7v being full and 12v somewhere in the 35% to 50% range depending on make/model/type/chemistry

All the electrical system on a car is designed to deal with that range of voltages, and all electric or electronic components run on differing voltages. Some on a set voltage, some on a range. Some at 5v, some at 1.2v, some at 12v, some at 17v, some in some cars even at 40v or 60v, some at any voltage it happens to be available.

Each component will have its own form of power regulation to grab that electricity from the battery/alternator, at whichever voltage it happens to be, and convert it to whichever flavour of voltage it desires. By means of regulators, buck/boost converters, and even 3 phase high voltage set ups.

The ECU for example, has it's own power distribution unit, and will work with anything between 7v and 17v+. It will take that, and then feed specific voltages to specific modules and components.

All of the above, comes exclusively from the battery and/or alternator.

It does not matter if the battery is under the hood or under another car's hood. And it doesn;t matter if that battery/power source is giving out 11v or 15v, becuase that's what the battery under the hood would be doing anyway

I wouldn't but I design electronics for a living, have built cars and have a reasonable understanding of how their electrics work. Details differ but the basics of a non-hybrid haven't changed much.

How would jump starting achieve that?

Me either!

Jk

I think you’re misunderstanding what’s being said. I have never suggested there’s another source of electricity on a car, I said not everything has a 12v supply directly from the battery and I am correct. 
 

i think they’re very different, brand to brand, but we’re obviously looking from different angles  

achieve what? 

Jim 

Ay, probably.

Wrong power in the wrong place.

Jk

I’m not sure why you think it would be the wrong power in the wrong place. I feel like we’re at cross purposes again. 
 

anyway, to summarise. I didn’t disagree with your opinion that a jump starting cannot spike an ECU, I’ve never known either way. But now knowing your profession I’m tempted to agree with you. 
 

I corrected you on a statement about everything being supplied directly from the battery when it’s not. I accept that probably isn’t quite what you meant. For my part, I never assume things will be as I expect them to be, and my statement read as such. 
 

Mr Lopez also got involved and misunderstood what was going on and I’ve remembered why I don’t argue with people on the internet. I’ve got a rucksack to pack and a wall to point and no time for this shit. 
 

Hopefully everyone gets out climbing this weekend and has a good time. 
 

cheers

jim

I don't think that would result from jump starting but that's what you appeared to be suggesting.

I never said everything is directly powered from the battery.

Everything is ultimately powered from the battery or at least the alternator but that's probably more of a philosophical point than a practical one in this context. Everything that is powered from the battery or connected to the 12V system is designed tough to be connected to what is a very ugly chaotic supply. To me it simply goes without saying that many of the electronic circuits are indirectly powered from the battery in as much as they sit behind filters and voltage regulator(s) and in some cases, galvanic isolators. Almost all modern digital circuits run at 5V, 3.3 or 3.0, often an ugly mix. I know full well there are different power busses in most vehicles, my kitcar for example provides a nice clean +5V power line out into the engine loom for sensors but that's not of interest when considering the damage an unstable, 'spiked' battery voltage could do because if the filters and regulator are working they protect the stuff on the 5V bus from chaos on the '12V' supply, if they aren't working then it's the ECU where that regulator resides which you would consider to have been damaged and that is connected directly to the battery (and indirectly via relays and switches). Another example everyone will be familiar with is the USB ports many modern cars have for charging, obviously a 5V supply intended for 5V devices but still ultimately powered from the 12V system.

Sure, there is also some niche stuff out there we might not consider properly hybrid but that has higher voltage circuits available for/from starter/generator/hybrid-drive other high power systems systems but it will tend to be robustly isolated from the '12V' system for safety. Big diesel BMWs for example run a 48V (IIRC) starter/generator system which provides reliable stop-start in traffic and also operates as a low speed parallel traction motor to backfill the torque curve while the ludicrously complicated turbo system spools up.

When talking about stuff the 12V supply could damage which is what we're discussing in the context of jumpstarting it doesn't make sense to consider the components hiding from it downstream of regulators and isolators.

jk

Is it not possible for these regulators to be fried by a voltage spike? 

It occurred to me the other day why a voltage spike may result from jump starting. When cranking the dead car, the alternator on the jumper car is going detect the voltage drop, and work to it's maximum capacity. Starter motor being the biggest demand it's going to make the alternator work hard.

This isn't going to happen when you just start a car normally as the alternator isn't doing anything productive.

Dead car starts, starter motor disengages, and there will be a period where the alternator is still working at full capacity with almost no load on it. I assume this could then result in a dump load.

I would assume regulators for ECUs etc are designed for such load dumps, but perhaps if the jumper car is being revved high so the alternator can create maximum power it's just beyond what these components can handle, once they've had a decade of aging.

If the above has any merit, then make sure the jumper car is revving hard when the donor is cranked, and/or, turn some lights on, or, if the dead battery has enough life left in it, only jump to charge, knock the jumper car off, leave the cables connected, and then try and crank the dead car.

Yes.

Being an inductive device it's not possible to instantly shut down an alternator's excitation or output current when a load is suddenly removed and that will tend to result in a sudden increase in output voltage. I'd assume if the alternator's output impedance and the car battery as load were insufficient alone to clamp that within safe limits there would be a a Zener output clamp built into modern alternator regulators. I don't see it on the generic schematics a quick google throws up but that doesn't mean much.

There is a reason there is a whole class of automotive qualified electronic devices, it is a nasty messy power supply (and often a hot vibrating environment) but that is well known and accounted for.

Equipment connected to the 12V supply will certainly be designed to handle significant transient overvoltage and absorb that power but with a working regulator on the alternator it should only ever be transient.

If the '12V' bus voltage significantly exceeds the maximum design voltage for a significant time period it's a race to the death between the input filter/clamp circuits in each module and the vehicle fuse feeding them but that's not likely what we're thinking about with a jump start gone wrong.

jk

Politely remind the dealer of the Consumer Rights Act https://www.legislation.gov.uk/ukpga/2015/15/contents/enacted) Right to Repair or Replacement clauses especially relevant here, and his obligation to repair (fully at his own expense) within the first six months after sale. Since you've already paid him £200 for a repair which didn't work, you're already in refund territory.

He is making claims about the jump start causing the damage: he might even be right but this is very hard to prove (ask him to show you proof from diagnostic codes, etc.)

Do all communication in writing and ask for a reply in writing as you may need to provide this to Country Court do not let the dealer talk round stuff on the phone.

If he blocks this avenue, then tell him that you are taking it elsewhere for repair, but you will claim the cost back in the County Court through a small claims process.

My own experience of this was that it took a long time - nearly a year from the car breaking down - but I eventually got him into court, negotiated an agreement for about 2/3 payment, and a court order to pay it within two weeks, and it was paid. This was for the full cost of a replacement engine at £6000+.

Thanks kmsands and all

Heres where they are at.

Car repaired last week and it wouldn’t start again when they got it home.

AA man came and he could only start it by pressing the battery relay.

The car was dropped at a garage that the owners son asked them to take it to, and my daughter asked for a refund. The son said he would ask his father.

The man at the garage ( not owned by the seller) advised my daughter to look at consumer rights and was perturbed that they had been charged £200 for the original fix of the ECU.

My daughter had a phone call from the sellers father( they are independent car sellers) and he was quite aggressive saying that it was the key and that he had started it ten times in a row.

He has said he is going to get a new key cut and ignored the refund request.

Are they still within their rights for a full refund or do they have to go along and try the new key?

thansk a lot

dave

 Took a few fried alternators for people who installed lifepo4 batteries, charged with a dedicated alternator, and had the BMS triggering battery shut down, to figure out that dropping a lead acid battery in the bank is enough to suppress the spike.

 And as the running alternator is in the donor car you'd expect any damage if there were to be any, to be done in the donor car as much as in the jumpstarted one

I'm no expert, but when I had a problem which turned out to be the key - it clearly registered as a fault on the diagnostics.

So it would seem odd that the fault wasn't spotted when they first had it back, and should have run diagnostics?