What precaution must be taken before welding on a vehicle with electronic engine controls?

Before welding on a vehicle equipped with electronic engine controls, it is crucial to disconnect the ECM (Engine Control Module) from the vehicle's power supply. This precaution helps to safeguard the sensitive components of the vehicle's electronic system from potential damage caused by the electrical currents generated during the welding process.

Welding involves high currents and voltages that can create voltage spikes and induced currents, potentially harming the delicate circuits within the ECM. Disconnecting it prevents these harmful electrical effects and ensures the integrity of the vehicle's electronic systems.

In contrast, recording fault codes is beneficial for diagnosing issues but does not protect the ECM during welding. Attaching the welder's ground clamp to the ECM itself poses a risk because it can allow welding currents to flow through the ECM, leading to damage. Using reverse polarity for connections during welding does not provide any specific protection to the electronic components and could have the same detrimental effects as grounding the ECM directly. Thus, disconnecting the ECM is the most effective and essential precaution in this scenario.