FYI: Check engine light and A/C compressor - Mercedes-Benz Forum

LinkBack Thread Tools Display Modes
post #1 of 1 (permalink) Old 08-10-2009, 09:33 AM Thread Starter
BenzWorld Junior Member
Date registered: Jul 2009
Vehicle: 1990 300 SE
Posts: 6
Mentioned: 0 Post(s)
Quoted: 0 Post(s)
(Thread Starter)
Smile FYI: Check engine light and A/C compressor

I got a lot of answers from this, I would like to share something....

I bought a 1990 300 SE two month ago. The car is great, however, two items the previous owner could not resolve:

1) Check engine light - code indicates O2 sensor. He changed it and could never clear the check engine light. Of course, in California, this will not pass the smog.

2) A/C compressor does not engage even when the refrigerant is full.

I took the car to a mechanic, and he was able to jump the A/C compressor. He told me the compressor is good. There is something that is controlling the compressor and it's not working properly.

After research and looking through the repair manual, I found out that the Electronic Control Unit (ECU) (also called MAS Control Unit) controls the A/C compressor and the O2 sensor. I ordered one from Auto Parts at AutohausAZ - OEM Auto Parts - Discount Replacement Parts, Resources and Car Care Tips ( $ 260.00 ). I replaced it, unplug the battery for an hour or so, and guess what? It's all good.

AC works, Check engine light is out. I have been driving it for two day now and it's all good.
samhs is offline  
Sponsored Links

  Mercedes-Benz Forum > General Mercedes-Benz Forums > General Mercedes-Benz

Quick Reply

Register Now

In order to be able to post messages on the Mercedes-Benz Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


  • Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
    Thread Tools
    Show Printable Version Show Printable Version
    Email this Page Email this Page
    Display Modes
    Linear Mode Linear Mode

    Similar Threads
    Topic Author Forum Replies Last Post
    Check engine light and flashing Low gas light benz3000 W210 E-Class 4 08-04-2009 01:17 PM
    1997 S420 Fuel gage light flasehs setting Check Engine light aljabari W140 S-Class 7 09-03-2007 09:19 PM
    How to check code for check engine light 94 E320 W124 Synd W124 E,CE,D,TD Class 1 05-24-2007 02:37 PM
    would blown dashboard light make check engine light go on? ae98 R170 SLK-Class 3 10-07-2006 12:36 AM
    check engine light & flashing fuel guage light pd99sl500 R129 SL-Class 7 02-27-2005 04:31 PM

    Posting Rules  
    You may post new threads
    You may post replies
    You may not post attachments
    You may not edit your posts

    BB code is On
    Smilies are On
    [IMG] code is On
    HTML code is Off
    Trackbacks are On
    Pingbacks are On
    Refbacks are On


    Title goes here

    video goes here
    description goes here. Read Full Story
    For the best viewing experience please update your browser to Google Chrome