Before welding on a vehicle equipped with electronic engine controls, what must you do?

• A. Record all fault codes.
• B. Attach the welder's ground clamp to the ECM.
• C. Attach the welding connections using reverse polarity.
• D. Disconnect the ECM from the vehicle's power supply.

Answer: (D)

When welding around electronic engine controls, the critical step is to isolate the control module from the vehicle’s power. Disconnecting the ECM from the power supply stops any welding-induced voltage spikes or stray currents from feeding into the module, protecting sensitive microprocessors and memory circuits from damage.

Recording fault codes doesn’t shield the electronics. Attaching the welder’s ground clamp to the ECM could push welding current directly into the module, risking harm. Reversing polarity isn’t a protective measure for electronic control units and can create other issues. So, removing power to the ECM is the correct approach.