Need to check each word. For technical terms like "ECM," "DTCs," since they are acronyms or parts of technical language, maybe leave them as they are unless instructed otherwise. The user didn't mention acronyms, so perhaps replace them if they are not proper nouns. "ECM" is a common term in automotive context, so maybe don't replace it unless necessary. Wait, "engine control module" is the full form, but "ECM" is an acronym. The user said no changes to proper nouns. "ECM" might be considered as part of the proper noun "ECM 2001 6.3," so that should remain. Similarly, "DTCs" is an acronym for Diagnostic Trouble Codes, but since it's written as DTCs, it's an abbreviation and should be left as is if it's part of proper terminology. The user might consider those as technical terms that shouldn't be changed.
Now, I need to ensure that no proper nouns like ECM 2001 6.3 or MHH AUTO are altered. They should remain unchanged. Each substitution should be in the syn3 format. Let me go through each sentence again and apply the synonyms where appropriate. ECM 2001 6.3 - MHH AUTO - Page 1
For "on-board diagnostics (OBD) system", "on-board" could be vehicle-mounted, embedded, or integrated. "System" might be unit, mechanism, or apparatus. Need to check each word
Let me start processing word by word. First sentence: "MHH AUTO is a top-tier vendor of technical manuals and restore information for the automotive industry." "ECM" is a common term in automotive context,
But applying this to the entire text might be time-consuming. Also, need to check that the synonyms make sense in context. For instance, replacing "provider" with vendor makes sense. "Repair" could be rebuild. However, some words might have limited synonyms, so need to be careful.