Jump start kils ECU

Sounds like a make to avoid, then, with such badly designed electronics.

Applies to all makes without a load dump suppressor. Switching the headlamps & rear demister on before disconnecting the jump leads avoids most of it.

Not really; last vehicle I had direct experience of in this regard was a VW.

Chris

This is a classic case of a correlation NOT providing proof of a causal relationship. For example - many people whose vehicles won't start will keep trying until the battery is too flat to turn the engine. The next thing they try is a jump start... An ECU fault may have been the reason for the original non-starting - but it is subsequently interpreted as having been *caused* by the attempts to jump start.

It is possible that jump starts are the major cause of ECU failure but it would take more than an anecdotal account of a correlation to provide good evidence for the causal relationship.

But in this case, it would be a huge coincidence that the non-start was caused by ECU failure; the battery was clearly flat before the non-start condition.

In the other case that I have knowledge of, the vehicle was left for a number of weeks, and the battery was too flat to start it also, so there was a reason other than ECU failure for the non-start.

The AA are not noted for spending money unnecessarily; they are a commercial operation, after all. They invested heavily a number of years ago in devices to prevent spiking ECU's when jump-starting, and patrols were threatened with disciplinary action if they failed to use them.

Chris

Load dump suppressor? Is that a polite name for a voltage regulator?

I didn't express a view about whether or not this particular case might have been related to jump starting. However, the flat battery might, for example, have been due to a loose battery terminal with intermittent disconnects or a defect in the battery itself, either of which can also cause voltage spikes and ECU damage in an unprotected ECU.

So that's a sample size of 2 from your experience. Both vehicles with possible dodgy batteries or connections. Hardly the basis for a generalisation.

The AA example proves nothing. I didn't say that a jump start could

*never* cause an ECU fault. I simply disputed that the *evidence presented* was sufficient to support the view that jump starts are the main cause of ECU failure. It might be true but one would need better evidence before coming to that conclusion.

Most people dont have a clue how to jump start a vehicle correctly anyway.

you should never connect the earth (usally negative) directly to the battery

If they provide jump start points use them

When you have connected the cables up correcttly allow the donor vehicle to run for approx 10 minutes to partially charge the dead vehicles battery

No, the voltage reg controls the field coils, the suppressor either directly trys to clamp the peak voltage or just crowbars the output.

On Thu, 28 [...]

As I explained, in the first case the battery was flat having been used to bleed through a diesel that had run out of fuel, and in the second case it was a vehicle that had been unused for a number of weeks.

No dodgy batteries/ connections. (See above.)

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Why not? Why would they invest in extra equipment and training if they hadn't seen spiked ECU's caused by wrong jump-starting? I'm not trying to

*prove* anything BTW; just perhaps save someone some unnecessary expense.

Re-read my original post; It's addressed 'To the nay-sayers...'

There are some regulars who post here who in the past *have* said that jump-starting cannot spike an ECU.

I never said that jump-starts are the *main* cause of ECU failure; I said that the company that repairs them finds that it's a common reason for such failures.

Chris

I'm talking about the voltage regulator in the ECU. The design of that should be perfectly capable of handling any spikes - even although I'm not convinced they occur. If it can't, it's badly designed. And how come it's always the ECU that suffers - not any of the other electronic equipment on the car? How come they seem to be designed to cope with these 'spikes' or whatever - but the most essential bit, the ECU - can't?

In that case they're all badly designed, they all regulate the field current. Look up load dump, Bosch have published quite a lot on them, there's a whole set of standardswritten

Nobody else has suggested they don't affect other things.

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The problem is that when you make the last connection the two systems are at different voltages, so a spark may occur. It's likely that both batteries are gassing, so there's a *very* small chance of an explosion.

Standard advice is to make the final earth connection directly to a point on the engine block, and as far from the battery as possible.

I understand your thinking, but in practice leaving them connected for a while seems to cause no problem. It's disconnecting under the situation that the two batteries have greatly different states of charge that cause the problem. Leaving them connected and running mitigates that to some degree.

A completely flat battery would usually need more than 10 minutes of running at tickover in order to have sufficient charge to restart the vehicle. Even twice that time might be insufficient.

I doubt that you've jump-started as many vehicles as the motoring organisations do in a year, and they deem the problem to be of sufficient magnitude to make it worth while taking precautions.

Bear in mind the key factor in mass-market car design is cost; if a designer can save a few pounds on every car, even at the expense of some reduction in service life or reliability, (s)he would be hailed as a hero!

Chris

You are saying every single new car has the alternator controlled by the engine management system? I find that very hard to believe. I know it is done with some. But in any case it makes no difference - a well designed one would provide protection on that input. After all, jump starting isn't exactly uncommon.

Quite. A battery has a very low impedance so why add to this by not connecting directly to it? Some cars - like BMW - do have dedicated jump start points under the bonnet - but this is just for added convenience since the battery is in the boot.

With some alternators, if a battery is totally fooked, they wont produce a charge. And if they do and it is, may produce rather more than the nominal

12 volts. The best way is to charge the flat battery off the donor car for a few minutes, if it has shown no signs of life. Then disconnect, and see if the flat battery has taken a charge. if it has, proceed as normal. If not, don't attempt a jump start.

Other thing is just how ready some makers are to produce a snap answer to a failure by blaming it on the user.

FFS, a battery doesn't 'gas' when flat. And when did you last see an 'open' type anyway?

No, you've just come up with that. Most aletrnator have the voltage reg built in, but they've never regulated the output, they regulate the current in the field coils to control the output, so there's a lag.

& has instructions on how to do it that are generally ignored.

They gas when they're knakered & charging though, and you normally disconnect whilst they're charging.

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Just about every Ford made since 1998 has.

But it's not something a car manufacturer particularly cares about.

Ford cover themselves by detailing in their handbooks the method for protecting against the disconnect surge.

Chris