Armagedon:
Chaversdad…a Mercedes mechanic…please buddy,excessive laughing I am told will endanger my health…Mercedes do not have mechanics they have fitters and there is a massive difference which is why he did not do as I have stated.
maybe, but the point i,m trying to make is there was no almighty bang or ecu,s being fried, the truck was exactly normal, and i have to admit on the twice i,ve jumped it off {after xmas hols} i,ve just pulled the forklift up next it and jumped it straight off with no probs at all, so maybe i was just lucky 3 times
We had several blown bord computers at about a grand a pop so doing it my way put my mind at rest at least. I carried my own jump leads and do it the way I was told, maybe we were unlucky several times:lol:
Chaversdad…you may be right or at least lucky but the guy who looks after my rig is rather good at it and when a local dealers mechanic burnt out 3 ecu’s jump starting a rig he knew what caused it and advised me how to jump a modern rig which is all I have passed on here.
When my Merc went flat after i waited for a collection for a few days i decided to read the manual for it because the batteries are at the rear of the unit (under the trailer) and i wanted to know if there was an alternative way to access them or the terminals. Sure enough there was, there are two terminals just alongside the adblue tank specially for jump starting. No mention of headlights on in the instruction manual, and nor did i put them on. It started straight away no problem. I’m struggling to understand the logic of a slave battery blowing a CPU,ECU or whatever they are. Why is that supposed to happen?
To be honest i’ve never known batteries conected up properly to blow ecu’s - the worst things are jump-packs or worse the “start” function found on some battery chargers.Most of the ecu problems we have encountered have been at bodybuilders or understandably once when someone put the leads on round the wrong way which resulted in about 5 smelly ecus.
Never had a problem starting trucks just by connecting the leads up properly.
Best thing I can suggest is whether you use another vehicle or a stater pack is connect the leads up with the ignition off on both vehicles and leave it for 10 -15 seconds at least so that some charge can be passed to the dead battery. It is better to connect the negative lead to an earth point on the chassis of the dead vehicle.
In theory this minimizes potential for damage, turning the lights on IMO doesn’t do much if the dead unit is completely flat.
The only times I have seen an ECU pop is when some moron has connected the leads the wrong way round. FIZZLE FIZZLE!!!
I had to jump start an 05 TGA cabbed ERF last week at a customers premises, and we used the 58 plate Scania next to it with no problem and no turning of lights or electrics on.
when the fitter jumped my DAF i had to turn all my lights on before i he turned on the battery pack
as when we did it in the yard and did not turn on all lights and turned battery pack on and started engine, a red warning message came on the screen saying something like
“alternator voltage too high” or something like that.
Armagedon:
For the benefit of Conor…switching on the ignition is merely bringing into play a power source which is already in place
Why for my benefit? Related technical qualifications:
O level Physics with Electronics
O level Control Technology
BTEC HND in Electronics Engineering
CGLI 383 Pt2 Repair & Servicing of Road Vehicles.
Related experience:
Bench engineer Euromax Electronics dealing with circuits far more delicate than anything now that took a damned sight bigger spike than hooking up jump leads
Auto Electrician and Vehicle Mechanic in REME
Auto Electrician at Halfrauds
Mechanic at Arncliffe Nissan, Hull
Why do you think your comment is of any benefit to me?
…attaching jump leads is introducing an external source
And? Until the ignition key is turned on, the voltage and current flowing to the ECU is zero. When the key is turned, the voltage will be whatever the potential difference is between the two battery leads and the current flowing will only be that which the ECU wants to draw. You can’t force more current into the ECU than it wants to take and the voltage will only be that of the battery, the output of the alternator on the rescue vehicle or the recovered vehicle whichever is higher.
ask your pro mechanics what they do
Most of them nowadays are just fitters. The last “mechanic” I called out was from a Scania main dealer. Because his laptop was flat, he couldn’t diagnose the fault. I had to teach him how to use the dashboard warning lights to read the fault code.
Marmon:
I always thoght the best way was to turn off the battery masterswitch first, then connect jump leads, turn back on master switch then start up,.
We have several winners with the same comment.
And the fact that battery master switches don’t blow ECUs when you turn them back on is proof that Armageddon hasn’t got a flaming clue WTF he’s on about.
Armageddon, stick to being a spanner monkey fitter and leave the diagnosis to real mechanics who actually have a clue.
al_P:
turning on all the lights and gadgets would actually cause a power surge due to the massive amount of draw caused by everything been switched on , remember electricity is not pushed its pulled so if everything is switched on it will pull a massive amount of electricity , just like when the power comes on after a power cut at home everything goes bright for a few seconds.
The force which pushes the electrons causing them to swap atoms orderly and in the right direction is a potential difference placed across a conductor. This force ( electrical pressure ) is more commonly known by its unit of measurement VOLTAGE.
This is what happens when you read Wikipedia without actually knowing anything about the subject you’re commenting on.
I lost an eye jump starting a truck, the battery blew up in my face, it seems the vent holes on the water filler caps were blocked this caused a build up of gas in the battery. The spark from attaching the jump lead was enough to cause the explosion
al_P:
turning on all the lights and gadgets would actually cause a power surge due to the massive amount of draw caused by everything been switched on , remember electricity is not pushed its pulled so if everything is switched on it will pull a massive amount of electricity , just like when the power comes on after a power cut at home everything goes bright for a few seconds.
The force which pushes the electrons causing them to swap atoms orderly and in the right direction is a potential difference placed across a conductor. This force ( electrical pressure ) is more commonly known by its unit of measurement VOLTAGE.
This is what happens when you read Wikipedia without actually knowing anything about the subject you’re commenting on.
I did not have to go to wikipedia before commenting on this subject as i’m a mechanic by trade, just pointing out the original comment was incorrect, P.S. HAPPY JUMP STARTING
Armagedon:
protected from the sudden surge of 24 volts and this is done by switching on all the lights on the DEAD unit BEFORE jump leads are attached.
Surely you wouldn’t be able to turn the lights on if the battery is flat.
Armagedon:
protected from the sudden surge of 24 volts and this is done by switching on all the lights on the DEAD unit BEFORE jump leads are attached.
Surely you wouldn’t be able to turn the lights on if the battery is flat.
strangely if the battery not strong enough (or “dead”) to krank the starter motor it will power the lights, even on full beam they require less voltage i am assuming
IMHO a flat battery will, once the engine has been started pull a huge amount of current from the alternator, which it will not do under normal circumstances. This could cause an imbalance in the normal workings of the ECU which could cause a problem in this delicate and expensive piece of kit. Turning on lights, fans and everything else you can thing of will “pull” extra current through other parts of the electrical circuits and reduce that imbalance.
Me, I’ll always turn on everything when jump starting it really could save you or your boss a lot of money in the long run.
P.s. why do you think so many units run around with a sign on the back saying “DO NOT JUMP START” It’s to stop people doing it incorrectly and blowing the ECU.
Cruise Control:
strangely if the battery not strong enough (or “dead”) to krank the starter motor it will power the lights, even on full beam they require less voltage i am assuming
Less current yes, but current is not the same as voltage. The starter motor is by far the greatest drain on the battery set. Just think how much power is required to spin a 12 litre diesel engine over at high speed using an electric motor…
To differentiate between current and voltage, just think of two rivers, a little one and a big one.
Water flows down both rivers at two feet per second, that’s voltage.
Far more water passes down the big river, that’s current.
Cruise Control:
strangely if the battery not strong enough (or “dead”) to krank the starter motor it will power the lights, even on full beam they require less voltage i am assuming
Less current yes, but current is not the same as voltage. The starter motor is by far the greatest drain on the battery set. Just think how much power is required to spin a 12 litre diesel engine over at high speed using an electric motor…
To differentiate between current and voltage, just think of two rivers, a little one and a big one.
Water flows down both rivers at two feet per second, that’s voltage.
Far more water passes down the big river, that’s current.
Nice one Harry saved me from going into the big pipes little pipes plumbing analogy.
OK, I have read enough nonsense now, here is how you jump start a stricken truck.
Park within reach of your jump leads, with both ignition systems turned off then remove the battery covers.
Ideally, turn off both battery isolaters. If you have an analogue tachograph, this will cause a spike on the card, write on the back of the card later why this is.
Clean around the battery terminals with kitchen towel until you can clearly identify the positive and negative stamps on the top of each battery.
Connect the red jump lead from one positive terminal to the other. Wiggle the crocodile clips a bit so they bite through the dirt and muck and make a good connection.
Connect one end of the black jump lead to the negative terminal of the stricken vehicle, then connect the other clip to a good earth on the donor vehicle, facing away from both battery sets.
You should see a good strong spark, don’t worry, it can’t hurt you.
Turn both battery isolators back on, start the engine of the donor vehicle, run it for two or three minutes to send some Oomph across, turn on the ignition on the stricken vehicle and check the voltage, which should now be 26+ volts, then start the engine.
Allow it to run for a minute then disconnect the jump leads in reverse order.
they require less voltage i am assuming 
it would be quicker walking 