This might help.

http://www.peachparts.com/shopforum/tech-help/373037-importance-electrickery-your-mechanical-speedometer-w201-w124-based.html

I have recently learned that if the hall effect sensor on the back of the speedometer gauge is not working the O2 sensor by default runs in 60% error code. This is all well and good but if you switch of the ignition the fault gets erased from the fault code memory!

(If I was younger I'd do something like hashtag pain in the arse)

Something for you to check

Measure duty cycle before and after a drive (with out switching off the ignition remember).

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!