[saket77]

Though the correct procedure to jump start is connecting the negative lead from the booster battery to any unpainted metal part of the dead car, which is also a grounding point; but I still wonder why the car went into limp mode when you connected the negative leads of the batteries itself. Because the negative terminal is anyways grounded to the car or chassis frame and it is one and the same thing. As the screen shot of the manual states, it is advisable to use a grounding point (read away from the battery) is to avoid creating sparks near the battery which may be a hazard.

But why the limp mode, I cannot fathom.

[R2D2]

Originally Posted by phamilyman

I had to waste 5 hours on Sunday to get it rectified at the F.A.S.S - the faults were low battery voltage (service warning) and TCM voltage surge (due to the wrong way of jump starting)

I believe the reason the ECU went into limp mode was due to the voltage surge caused by attaching a fully charged battery to a low voltage system (by comparison) in your car & not due to the connection location of the jumper cables.

Which is a good idea if you consider surges and static can damage sensitive electronics. Better a limp mode than a busted & very expensive ECU that will instantly result in a non-functional car. Yes, going into limp mode is a major inconvenience but I'd be hopping mad if my car's ECU were to be fried.

3 things you could do:

a) Keep an eye on the battery. You get inexpensive voltage monitors that plug into a cigarette lighter socket to make you aware of the battery voltage every time you switch on the ignition. If the battery drops to <12.25 V overnight you have a battery problem.

b) Bench charge the battery and perform a battery Sp. Gr. and load check. My guess is the battery is not being charged fully and as a result running down sooner than expected even with light loads.

c) Get the alternator voltage and amps checked. Most alternators are tested at about 2000-2500 engine RPM with all auxiliary loads switched off to begin with and then with headlamps, AC and other loads switch on.

[Sutripta]

Originally Posted by phamilyman

The hits don't end there. The engineering stupidity is so galling, even a college student would find it laughable. All these cute lights are ON, but I can't crank my car!
Attachment 1819528
Attachment 1819529

Safety trumps cranking! Hazards - safety item. Cranking - On the ground huge safety item - in a courtroom - no. Product liability lawyers will rule in this case.

(In a similar vein, what do you think of the fact that in many cars actuation of an airbag also immobilises the car).

Originally Posted by R2D2

I believe the reason the ECU went into limp mode was due to the voltage surge caused by attaching a fully charged battery to a low voltage system (by comparison) in your car & not due to the connection location of the jumper cables.

+1

3 things you could do:

a) Keep an eye on the battery. You get inexpensive voltage monitors that plug into a cigarette lighter socket to make you aware of the battery voltage every time you switch on the ignition. If the battery drops to <12.25 V overnight you have a battery problem.

b) Bench charge the battery and perform a battery Sp. Gr. and load check. My guess is the battery is not being charged fully and as a result running down sooner than expected even with light loads.

c) Get the alternator voltage and amps checked. Most alternators are tested at about 2000-2500 engine RPM with all auxiliary loads switched off to begin with and then with headlamps, AC and other loads switch on.

d) Don't use hazards for extended periods of time!

Regards
Sutripta

[audioholic]

Originally Posted by phamilyman

TL;DR - Puny battery can be discharged in 2 hour of hazard lights. ECU prioritizes cute lighting over cranking engine. Don't get a local battery guy to jumpstart the car - wait for roadside assistance.Jump starting the wrong way puts ECU in limp home mode limited to 30 kph.

My dad had a similar experience two weeks back in our Celerio AMT. But in his case, he had left the car ignition in ON position and sat in the car for half hour with the music system, AC blower and alas, after that the car refused to crank. He has done this earlier with his SX4 even though the battery of it was older. But the major difference he wasnt aware of(which I was but hadnt explained to him ) is that in the Celerio AMT when you have the ignition in ON position without engine running, the transmission hydraulic pump runs every half a minute or so replenishing the oil pressure by a small amount. This drained the battery and then my dad had to call Maruti RSA or whatever. They came in 20 minutes and jumpstarted the car for 500 rupees. Steep, but he didnt want to take the risk of some random mechanic trying stuff and I too am not in station from quite sometime.

Two year old battery and neither me or him expected it to happen. But once we thought of the transmission pump we realised where the culprit was.

In the case of your Ford DCT, have you looked at this angle? I am not sure if the DCT is hydraulic or completely electric, but hazard lights alone might not drain the battery so much is my feeling. I can be wrong too.

[sgiitk]

My own 'algorithm' is. Positive to Positive, start the engine or the donor. Positive to Negative and then crank the dead vehicle. Disconnection is reverse. First negative out, then negative.

Some people also connect both, before starting. I had a case of a totally dead battery, so not connecting both the terminals may have helped.

[Aroy]

Originally Posted by sgiitk

My own 'algorithm' is. Positive to Positive, start the engine or the donor. Positive to Negative and then crank the dead vehicle. Disconnection is reverse. First negative out, then negative.

Some people also connect both, before starting. I had a case of a totally dead battery, so not connecting both the terminals may have helped.

Yes it is wise to start the donor engine before finishing the connection.

By the way, I guess you meant Negative to Negative and Not Positive to Negative.

[Jeroen]

Before you jump start a modern car, it makes sense to check the owner manual if there are any special requirements with respect to where you attach the jumper cables. I know most owners don’t, but it avoids having to troll the internet for suggestions

Usually positive to positive from the donor car battery to the dead battery.

But the negative cable is rarely connected to the dead battery terminal.

So for instance, I just checked the manual for our little Ford:

Connect the negative cable to a bare metal part of the car. As far away as possible from the battery, and the fuel injection system. Or attach it to one of the ground/earth points.

One reason for not have the negative cable connected to the dead battery terminal is to avoid any chances of battery gasses exploding due to sparking.

But it also provides better protection to surges if any.

Jeroen

[Miyata]

I have had to jump start quite a few cars in friends and family circles. Have given them a tutorial on how to do it too so next time they won't have to rely on me. Good thing is the tutorials here go with demonstrations.

Positive to positive.

Negative to some metal part under the hood a little away from battery.

Make sure to gently sandpaper scratch the place you are connecting the cables at.

Crank up the healthy car. Run it a while. Then try cranking up the dead car. Idle them for a few sec.

Remove the cables carefully without shorting them. Negative first then the positive.

And hence, among other things one keeps on a car, some sandpaper is good to have as well.

OT - I have tried engaging our apartment complex folks in trying to be helpful and setting up a tutorial for anyone interested, but I guess everyone learns when they really want to - not everyone can be a BHP'ian!

[Sutripta]

Originally Posted by Jeroen

One reason for not have the negative cable connected to the dead battery terminal is to avoid any chances of battery gasses exploding due to sparking.

But it also provides better protection to surges if any.

Jeroen

How?

Regards
Sutripta

[Jeroen]

Originally Posted by Sutripta

How?

Well, that is what some internets claim.

Me, I believe it makes sense as the return current does not have to flow all the way through the dead battery negative terminal and cable and then to the jumper cable.

Going from ground straight to the jumper cable ensures less Voltage drop. Does it make a huge difference? Not quite sure. I have never taken the trouble to measure it.

The explosion risk is real, although with modern sealed battery probably not an issue anymore. But on this sort of stuff better safe than sorry.

Jeroen

[Sutripta]

^^^
We were talking of surge, not ohmic drop.
Surge as seen where? And working backwards from there, how?

Regards
Sutripta

[Jeroen]

Originally Posted by Sutripta

^^^
We were talking of surge, not ohmic drop.
Surge as seen where? And working backwards from there, how?

I don’t know, maybe the internet was wrong?

Jeroen

[Sutripta]

^^^
Always a possibility. (Spotted errors in Wikipedia also!)

Regards
Sutripta

[Aroy]

Recollecting my college level physics.

The longer the path the greater the resistance (how ever small it may be). Further longer paths have a bit more capacitance and induction compared to shorter path. All this goes towards reducing the surge without substantially dropping the voltage.

[Miyata]

I think you folks are complicating this simple phenomena of electrical sparking - In most cases the sparking itself is unavoidable, but its consequences are avoidable. To avoid any unpleasant consequences is why we place the negative far enough away from any readily combustible gases (like hydrogen that might emerge from battery chemistry).

What is the electrical spark - just local gas/air ionization as a consequence of high enough electric field causing the breakdown.

It typically can happen with the very last connection one makes. There is a sudden surge of charge that flows when the final contact (negative to metal) is made that can cause the spark depending on the amount of charge flowing in and nature of the contacts (hence the need for good electrical contacts in those regions).

Really, there isn't much else to it.