What you need to know before welding
Having welding done on a car is nothing unusual these days and a workshop that tackles welding jobs regularly will know all the precautions necessary to protect the car’s electronics. Nevertheless, some technicians who are, perhaps, rarely called upon to do welding jobs could do a great deal of harm to the electronics if certain precautions are not taken.
There are some erroneous and misleading bits of advice floating around which are said to safeguard the electronics while welding is being done; it is often said that by simply disconnecting the battery earth the electronics system will be immune to harmful surges.
Some mechanics do not disconnect the battery earth and claim that if the ignition is switched off the electronics are unaffected by welding spikes caused during MIG, TIG or arc welding. I also know people who take no such precautions and have done welding on many cars without harming the electronics.
Being a timid type, if I did a lot of welding work on cars I would invest in a surge protection device. However, these are not cheap and hardly worth the expense for the average once-a-year DIY man.
If you plan to weld something without removing it from the car, play safe and remove any electronic items in or near the proposed welding area and disconnect any others.
If this all seems like too much trouble, you may well get away with it, but price out the possible consequences before you start. I would recommend removing the item from the car for the actual welding.
Most people imagine that it’s the welder's voltage that does the damage, but that is not so. When the arc is switched off a dangerous voltage spike occurs. During welding a strong electromagnetic field is created. Switching off, as one would imagine, causes this field to collapse. The danger is that this collapse may bring a voltage pulse to electrical circuits in the area - even those that are electrically isolated from the welding current’s path. Thus, it makes sense to remove or disconnect any electronic devices in or near the danger area.
Although, as I have said, many people jump in and weld away, taking no precautions, I would advise the utmost caution. Components at risk include the air-bag system; alternator; engine-management system; in-car entertainment system; car alarm and, of course, several sensors.
If you decide to have the job done professionally - and to my mind this is the best way to go - first check that everything is in working order. Then repeat the exercise with the man who will be doing the work looking on. It’s always best to play safe. If everything works when you take the car in, be certain that everything still works when the job has been done.
Go only to a reputable workshop. It might be a good idea to ask around the local trade for a recommendation. Go by reputation, not price.
Do not forget that any person in the immediate vicinity with a heart pacemaker should be extra cautious. Voltage pulses could prove fatal. - Star Motoring