A 90 reading is the dreaded "Current to electrohydraulic actuator implausible." This is accompanied by the following footnote:
"The plausibility of the road speed signal can only be checked by the KE control unit when driving. If an implausible road signal is recognized when driving, the control unit "sets" the on/off ratio of 60% and stores this. The fault is not erased unit the ingnition is switched off. A "60% on/off ratio" test is performed, e.g. in dealing with the complaint [of] jerking when vehicle moving and throttle valve closed."
I got this reading once on my late 300E. I concluded that it had something to do with the road speed sensor. But then it did not reappear so I never pursued it further. I have always been curious about what it really means.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe