On my new toy, a 1992 500E (124-036) I’m getting a “code 8” on the “distributor ignition” computer, which translates into “transmission overload protection switch does not close”. I understand the function of this system (to retard engine timing during full throttle upshifts) but I am trying to diagnose the cause of the switch malfunction, as well as understand how the switch itself works.

A shop with a good history on MBZ transmissions apparently rebuilt the transmission two years ago; I don’t know if this problem is new, or if it has existed since the transmission was rebuilt – thus my concern whether it may be something internal vs. the switch itself. In the transmission diagrams, there is a pin and a “reaction valve” behind the switch - my concern is if either of these parts could be defective. My questions:

Is the switch itself a common failure point?
Can the switch be tested (and how)?
Is the reaction valve or pin a possible failure point?


Thanks in advance for your help…

__________________
Current rolling stock:
2001 E55 183,000+ Newest member of the fleet.
2002 E320 83,000 - The "cream-puff"!
1992 500E 217,000+
1995 E300D 412,000+
1998 E300D 155,000+
2001 E320 227,000+
2001 E320 Wagon, 177,000+

Prior MBZ’s:
1952 220 Cab A
1966 300SE
1971 280SE
1973 350SLC (euro)
1980 450SLC
1980 450SLC (#2)
1978 450SLC 5.0
1984 300D ~243,000 & fondly remembered
1993 500E - sorely missed.
1975 VW Scirocco w/ slightly de-tuned Super-Vee engine - Sold after 30+ years.