Warning! Jump-starting may damage your ECU

With reference to the recent post by Stuart ‘vrcorrado’ ‘Help, my 2003 TD4 won’t start’

It now seems almost certain that the ECU sustained some damage during attempts to ‘jump start’ the vehicle after the battery became ‘flat’ due to the lights having been inadvertently left on. Prior to this the vehicle had been running well with no charging system faults etc.
The vehicle is now operational once again following £300 worth of ECU and associated component repairs.

So what’s the answer?

If you’re a member you will call your preferred motoring organisation who will send a highly trained and well equipped patrol to restart the vehicle at minimum risk to the ECU. And should anything go wrong they will usually reimburse the repair costs.

If you prefer to help yourself and reach for the ‘jump-leads’ hanging on the garage wall, do you have a set procedure to follow which will avoid damage?

Let’s have your thoughts about DIY jump starting procedures.

With thanks to Stuart.

Dann said:

With reference to the recent post by Stuart ‘vrcorrado’ ‘Help, my 2003 TD4 won’t start’

It now seems almost certain that the ECU sustained some damage during attempts to ‘jump start’ the vehicle after the battery became ‘flat’ due to the lights having been inadvertently left on. Prior to this the vehicle had been running well with no charging system faults etc.
The vehicle is now operational once again following £300 worth of ECU and associated component repairs.

So what’s the answer?

If you’re a member you will call your preferred motoring organisation who will send a highly trained and well equipped patrol to restart the vehicle at minimum risk to the ECU. And should anything go wrong they will usually reimburse the repair costs.

If you prefer to help yourself and reach for the ‘jump-leads’ hanging on the garage wall, do you have a set procedure to follow which will avoid damage?

Let’s have your thoughts about DIY jump starting procedures.

With thanks to Stuart.

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I prefer to use jump packs. I have 2. One is on charge while I am using the other one.

Anti surge protectors that allow 'soft starting' are available for about £10. these help prevent spiking the ecu. Turning the headlights on can help prevent spiking the ecu.

If you have none of the above then turn the lights on on the casualty vehicle and the engine off on the assisting vehicle before connecting the jump leads. Then start the engine on the assisting vehicle. You can now turn the headlights off on the casualty vehicle. Wait for a few mins before attempting to start the casualty vehicle. Most cheap halfords jump leads cannot carry enough current to jump start a landrover. They can however charge the battery (hence waiting a few minutes before starting).

having been a fitter most of my working life, the biggest cause of fecking ecu,s up is using booster battery chargers and i have never had a problem using jump leads, ive seen damage done by connecting the batterys up the wrong way and also by some tossers using a 24 volt system to jump start a 12 volt system, on ecu,s on goods vehicles i do repair them the cost of repairing these is about a 1/5 of the cost of buying a new 1 but i have not done any 12 volt as yet but noe saying that i think i will get hold of 1 or 2 and try,

Thanks guys, so what's an easy way of making sure 'non-technical' folks get the polarity right in the first place? D..

Dann said:

Thanks guys, so what's an easy way of making sure 'non-technical' folks get the polarity right in the first place? D..

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ignore the colour of your cars battery leads and look for the + and - symbols on the actual battery. They should be near the connector posts.

pos to pos neg to neg you can bet your life that if there is a booster start on a battery charger it will get used to start a vehicle.

Brilliant and thanks Ratty.

make sure that the negative is connected to the engine block and not the battery on the vehicle that needs boosting when using jump leads.

brnocz said:

pos to pos neg to neg you can bet your life that if there is a booster start on a battery charger it will get used to start a vehicle.

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Ta brnocz: I'm thinking more in terms of folks getting a 'jump-start' off their partners/neighbours car on their driveway. Hopefully if the garage fried the ECU using 'Booster' they'd own up. Wouldn't they?

howardo said:

make sure that the negative is connected to the engine block and not the battery on the vehicle that needs boosting when using jump leads.

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Yes, that's what I've always been taught.

howardo said:

make sure that the negative is connected to the engine block and not the battery on the vehicle that needs boosting when using jump leads.

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For those that don't know why this is......If a 12v battery has a cell gone down it becomes a 10v battery. If you try and jump start by connecting to the positive and negative terminals it can still only take 10v even though the assisting cars alternator may be pumping out 14.5v. It's like having a 2 litre coke bottle with the top cut off. It may have been 2 litres before but it aint any more. If you try and fit 2 litres in it it just aint happening. By connecting the negative to a suitable place on the engine it means that the vehicle is getting the full charge from the assisting vehicle. You are in effect using its battery instead of yours.

in reply to garages owning up i doubt that very much a fitter isnt going to own up to his boss that he fecked up on some thing i was a work shop manager and it was happening all the time it was ok when it left here or it was like that when it came in, as for starting on drive ways using jump leads isnt a problem most problems are caused by error if in doubt ask some one who knows,

If the negative (black) lead was first connected engine block to engine block just leaving the positive (red) to connect to battery positive on each vehicle would this ensure that wrong polarity could not happen?

Dann said:

If the negative (black) lead was first connected engine block to engine block just leaving the positive (red) to connect to battery positive on each vehicle would this ensure that wrong polarity could not happen?

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The negative should only be connected to the engine block on he casualty vehicle. NOT the assisting vehicle. On the assisting vehicle it should go to the negative on the battery.

Dann said:

If the negative (black) lead was first connected engine block to engine block just leaving the positive (red) to connect to battery positive on each vehicle would this ensure that wrong polarity could not happen?

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NO.
connect pos on flat bat to pos on good bat.
then connect neg on good bat to engine block on car with flat bat.

i have just taken this from a manual after starting the vehical from a another vehical switch lights and wipers on then disconect the jump leads

ratty said:

The negative should only be connected to the engine block on he casualty vehicle. NOT the assisting vehicle. On the assisting vehicle it should go to the negative on the battery.

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O.K. so there is still the possibiity of the inexperienced getting the polarity wrong. Do you think it's posible to teach somebody to carry out this procedure safely via text on the forum?

dann send me a private message and i will send a pic of jump leading a vehicle

brnocz said:

dann send me a private message and i will send a pic of jump leading a vehicle

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ta brnocz, can you post up (if it's not copyright) I've been doing this stuff for years. I'm just wanting to get some info out for the non-motor trade folks. Thanks d..

Dann said:

O.K. so there is still the possibiity of the inexperienced getting the polarity wrong. Do you think it's posible to teach somebody to carry out this procedure safely via text on the forum?

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yes.

1) park assisting vehicle as close to casualty vehicle as possible but making sure that the vehicles do not touch at any time.

2) open the bonnet on both vehicles

3)turn off the engine of the assisting vehicle

4)turn on the headlights of the casualty vehicle

5) Ignore the colour of the wires connected to the batteries. Instead look for the + symbol on both batteries (there should be a + and - symbol on both batteries near to the connection posts). Connect the + of the assisting vehicle to the + on the casualty vehicle using the red jump lead.

6) connect the negative (black) jump lead from the - on the assisting vehicle to the engine block of the casualty vehicle. (most engines have metal lifting eyes or alternator brackets etc to attatch the negative to)

7) turn off the headlights on the casualty vehicle

8) start the engine of the assisting vehicle

9) STOP. Do NOTHING. do not attempt to start the casualty vehicle. Let the battery charge for a few minutes first. The longer you leave it, the better the chance of the casualty vehicle starting. (5 mins should be plenty).

10) start casualty vehicle

11) remove positive (red) jump lead from both vehicles.

12) remove negative jump lead from both vehicles

13) close bonnets

14) go for a 20 minute drive. DO NOT TURN THE ENGINE OFF UNTIL YOU HAVE DONE THIS. 20 mins od driving should recharge your battery assuming that your alternator is working fine and that your battery can hold a charge