W140 Pushbutton Control Module - Supercession Interchangeability?

[jgl1]

Trying to track down a climate control problem (no heat) on a '93 500 SEL. HHT query of the ACC reveals no faults codes other than a defective aux. coolant pump. Using M-B's Electrical Test Program reveals the possibility of a couple of other faults, one of which is the pushbutton control module.

The vehicle's VIN suggests it was factory equipped with module # 140 830 20 85.

Yet inspection of the vehicle reveals the presence of module # 140 830 06 85... parts revision history shows this was superceded by 140 830 08 85, which in turn was replaced by 140 830 15 85 and then finally 140 830 20 85. But, according to M-B, the vehicle should have left the factory with the 20 85 module.

The vehicle's pushbutton control module was "renewed" a couple of years ago by an independent, so it is possible that is the source of the 06 85. The ACC has worked properly since that service, until now.


So, the question is: should the correct version of the pushbutton control module be installed and the Electrical Test Program rerun or is any version of this module suitable for use?