So many unknowns there, it depends on several factors. Most vehicle manufactures say not to weld on frames. who made the bumper? What does that maker say about recovery points? Most aftermarket winch bumpers have recovery points or designed points to install them.
I'm guessing you are not planning to remove the bumper from your vehicle to weld on it? If you are going to weld while it's bolted on, you need to take the same precautions when welding on the bumper as you would while welding on the frame.
– Always disconnect the negative battery terminal from the vehicle so that you open the electrical circuits in your vehicle to your battery, thus reducing the risk of over voltage situations which may damage your vehicle’s onboard computer.
–Always place the welding ground clamp as close as possible to your welding arc to minimize the electrical path between your arc and your
ground, therefore, reducing the risk of high voltage reaching your vehicle’s sensitive computer components.
–Always disconnect the airbag plugs under the hood of your vehicle. There is a slight chance that some welding voltage reaches your airbags and triggers them to go off.
This is the last thing you want since airbags are not only very expensive but once airbags are deployed, your vehicle might be required to have a “salvage title” from then on.
Following these precautionary steps eliminates almost all the risk associated with welding on your vehicle (regarding damaging on-board
computer components), but if you want to reduce risk completely, your best option is to completely disconnect your vehicle’s ECU.
Disconnecting your vehicle’s ECU has its own implications such as potentially disrupting the OBD2 system, and vehicle power/air-fuel maps.
If you have ever investigated replacing an ECU, they can sometimes be very expensive. Sometimes ranging in the thousands of dollars!
Therefore, it is always wise to be conservative and careful with your on board computer system when considering welding on your vehicle frame.