Details About Volvo ETM Failures

Don Wilson, a retired metallurgical engineer, has posted a detailed analysis of the failures of 1999-2001 Volvo ETMs (Electronic Throttle Modules) at his web site, VexedVolvo. He has photos of a disassembled unit, clearly showing how the resistance film potentiometers wore through, and the wiper contacts picked up debris.


Image courtesy of VexedVolvo.org

Don's conclusion:

The construction of this potentiometer is obviously not suitable for the application. Considering that in the life of the car there will be multiple millions of cycles of the throttle, the action of the hard metallic finger tips riding on the soft thick film carbon resistor element is a designed-in shortcoming that will result in an estimated 100% or more, failure rate in the life of the Volvo automobile.

I am glad that I drive a throttle-by-cable car!

(HT: Autoblog)