I created a comprehensive document with all the trouble codes for all the computer systems on the W124 with M104 (HFM) engine.
Click here to download it (1MB PDF file). This was created directly from the factory service documentation in the WIS.
Please note that the HFM system has mostly 3-digit digital codes, so the LED blink codes are only somewhat useful. Each LED blink code can have several meanings, and without a digital scanner, you won't know which of the several different items is the root cause of the error. For example, blink code 20 for HFM can mean upper or lower partial load, rich or lean. You don't know which of the four possible combinations is the real problem, without the 3-digit digital codes (051, 052, 053, 054 all translate into analog code "20"). Also, there are over a dozen digital codes which have no analog translation (#'s 114-144), see page 16 of the PDF file.
The document linked above is for the W124+M104 engine only... for the W124+M119 (V8 engines),
click here.
For the W140 with M119.97x (V8 to 1995),
click here.
I don't yet have documents created for the W124 with M103 or diesel engines.
Final comment... for those people who insist that old OBD-1 systems like HFM and LH have no live data available...
click here to see a PDF file which proves them wrong. LH live data is on page 1, HFM live data is on page 2.
