When Mig (GMAW) or Stick (SMAW) welding on a vehicle, do you have to disconnect the battery?

Most importantly, for any arc welding the Return Current Clamp (and Workpiece Lead) should always be located as close as possible to the point of welding to minimize the possibility that welding current could stray into any wiring or other systems.  See the image below...

Vehicle Welding

Cars and trucks use the 'chassis' of the car as return current path.  The body then becomes an electrical conductor from the various devices in normal operation.  The chassis is normally grounded to the negative terminal of the battery, and this is why the negative terminal should be disconnected first (and reconnected last).  (Note:  the current return path in an arc welding circuit is not a 'ground'.)

Some modern car owner's manuals do specify that the battery must be disconnected before any arc welding.  (It possible that older vehicles this may not be required, however in all cases the manufacturer's requirements must be followed.)

There are other risks, such as damage to the Engine Control Unit (ECU) or Engine Control Module (ECM), or the possibility of accidentally triggering the airbag circuits.

The question specifies the GMAW and SMAW processes, however often the GTAW process is used on vehicles.  Depending upon the set-up GTAW may introduce radio frequency (RF or high frequency) energy which can damage electronic systems.

Disconnecting the battery can cause problems with loss of sensor memory on modern cars.  Some people use a 'boost box' that keeps the power to the control systems, however this may defeat the purpose of keeping eliminating the voltage to the microprocessor systems.

There are 'automotive surge protector' devices available to help prevent damage to the electrical system from welding, but I have no experience with them.

The bottom line is that there may not be 'one answer' to this question and if it was me, I would do some research on the requirements for a particular vehicle before welding on it.  For example, what are the risks of welding on a modern battery electric or hybrid vehicle where the battery packs are operating at hundreds of volts (as opposed to a standard car with a 12V-DC battery)?

Jim Galloway
Professor and Coordinator Welding Programs
Conestoga College


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