After 8 days of daily driving the CE light has come back on. I checked the DM and have a code 2.

Pin 8 shows code 9.
Pin 14 shows code 1 (clear).

The archives indicate the DM code 2 refers to a bad O2 sensor. Is this correct? What is code 9 for pin 8 (HFM)?

I have the two disc CD manual for the 124 but could only locate one page that describes the 16 pins found on the diagnostic connector. If the codes for the various pins are somewhere on the CD can someone direct me to them. I have looked and looked.

HFM module code 9 is implausable 02 sens signal..
You can easily check the sig/sensor w/dmm on that car by looking for a rich voltage when disconnecting the Fuel pressure regulator vac line and a lean reading by inducing a vac leak at the SOV vac line..
Looks like 02 sens time , but I would verify w/testing.. Connector is under rug-pass side

CD is Useless for codes
All-Data is great...

I resolved my problems by installing a new O2 sensor. Used the Bosch 13275 4-wire that others on this board have mentioned. All codes cleared and have remained absent for many months.

CE light has however now come back. DM shows a code 5 (EGR). All clear at pin 8. I checked the vacuum line at front of engine and the EGR valve. Both OK. Ran a speedometer cable down the tube from EGR valve to air intake as prescribed in Steve B's article. Cable would not run through completely to end (I ran it in about 36 inches) so I imagine I have a carbon deposit build up at air intake. I plan to detach tubing and check out. Will report back.

Disconnected the EGR tube at air intake. At least on the 1995 E320, this first required removing the forward two 10MM bolts holding the accelerator cable harness. The third bolt at the rear of the harness is difficult to access but does not need to be removed since the harness will pivot at this point providing adequate room to reach the EGR tube. The two 10mm bolts holding the tube come out easily. There is a gasket here but mine remained firmly attached to the air intake and so I left it alone since I did not have a new one.

However, the EGR tube itself would not come free. I had to detach tube at EGR valve and also disconnect tube holding bracket located at oil filter. Seems the 1995 model uses a tube that has an extended insert sleeve (about 1 inch long) that slides into the air intake assembly. My tube was not flush with the air assembly as shown in Steve Brotherton's article. Anyway, at this point I could blindly pick at the carbon build up in the tube using a short piece of clothes hanger wire. This was enough to then get the speedo cable freely through the tubing starting at the EGR valve end. Did a flush with Gunk and then brake cleaner. Wished I had compressed air available but still feel I got it very clean.

BTW I had first made a quick attempt to remove the tube from the engine compartment for cleaning since it was entirely free. However, it does not appear that this is something that is easy to do without removing other components. I was just happy to have gotten this far and left it in place for cleaning. A 1/4 " ratchet set with various extensions works good in the tight places but 3/8" will also work.

Hope I do not see a Code 5 pop up anytime soon and that these instructions will help others.