From the CD:
No voltage or ground at KE control unit or KE control unit faulty
Lambda setting too lean
O2 sensor faulty (short to ground)
OVP relay or fuse faulty
Lambda control tester faulty
IMHE, what is mostly likely happening is that your sensor is not sending out any voltage which the system interprets as lean and has gone to full "on" trying to richen it up.
You can unhook the sensor - it connects under the carpet in the right front pass compartment near the trans tunnel - and meaure the voltage from the sensor to ground, with your new Sears DMM.
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