The Power Electronics Modules (PEM) in a 1.5 Tesla Roadster relies on two 12 Volt DC brush motor squirrel cage fan to cool IGBT (Power Transistor) heat sinks, to maintain safe operating temperatures in the power output section of the inverter, and a second one to cool the drive motor.

This SPAL brand fan assemblies are fairly low tech device, equipped with brushes that wear down, shaft bearings that wear, and no built-in tachometer often inserted in more critical cooling fans.

Roadster firmware relies on current sensing to gauge fan operation, and as this part wears, it begins to operate outside expected current thresholds, eventually throwing PEM cooling errors. 

(There are other conditions that can cause PEM cooling errors - failure to perform routine PEM cleaning, failing cooling system ducting, and connector issues.) 

When combined with marginal and underrated fan cable connectors, this is one of the common failure points in a Roadster.

We recommend replacement of this vital cooling portion of the Roadster drive train every 5 years.