Here is the original thread, he never referred to it as a 300E
Bizzarro Overvoltage relay problem
On some models (whenever they went to a heated O2 sensor), the fuel pump relay also activates the O2 sensor heater as directed by the engine control module.
If the OVP fuse blows and the engine control module is dead, the EHA is not powered at all and the fuel injection system is then in Fixed Operating Mode. There is no Lambda in Fixed Operating Mode. In fixed operating mode the engine control unit can be removed and placed in the trunk, and the O2 sensor is doing about the same amount of work as the spare tire.