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Subject: The fix and how the Check Control works. (longish) Author: rick540 : member since April, 2007 : 1759 posts Posted on: 2007-07-21 20:07:18

After being awake all night trying to fix this, and having different errors cropping up every time I put it back in the car. I was also not able to find a working used unit as they all had some or other fault.

Here's the story, hope it helps somebody.

First look carefully at how it is wired to the car....
Link to CCM wiring Diagram

I tried resoldering the CCM, but it's covered in a hard redish resin that prevents any soldering.

What I did to solve the problem:

1) removed all the black plastic parts
2) Soaked it overnight in Paint thinners to soften the resin. (it did not seem to harm the plastic connectors and components)
3) Used a pressure jet of water to blast the soft resin off.
4) Used desoldering wick to remove the existing solder.
5) resoldered the entire thing (Use a multimeter to check the tracks on the board afterwards.....Trust me do this, as I found some with hairline breaks in the tracks, it's very, very badly made)
6) Changed the 25V 220 Capacitor (blue thing on the pic in the corner for good measure)

I still got new errors freakin me out when I put it back in the car. On closer inspection I found a cracked resistor pack. The pack contains 9 X 1KOhm precision resistors all connected to pin 1. I then made up my own pack using 8 X 1KOhm resistors. (The 9th is not used on the packs) You can see the broken resistor in the pic at the bottom.

Now it works just fine, repaired both units and have a spare in the glove compartment.




How the CCM Works:

I will try keep it simple, but it's electronic speak:

The CCM has 24 input "channels" each one connected to a sensor that ultimately form a 24 bit parallel binary number that is read, converted to the same number in serial form and sent to the instrument cluster regularly. If the number does not change nothing will be displayed. If the number does change, the cluster will look at which bit in the 24 bit number changed and display the relevant message.

The channels are all tied to ground through the relevant sensors. if there is any problem, such as low coolant, that circuit will open and the corresponding bit in the 24 Bit number will change from a 1 to a 0

This 000000000000000000000000 will = "check control OK"
This 000100000000000000000000 will = "Coolant Low" (coolant sensor tied to channel 4 is now open)

This 010100000000000000000000 Will = "PAS Fluid low" and "Coolant Low" (sensors tied to channels 2 and 4 are open circuit and not grounded)

and so on...

If anything out of the 24 is not grounded, you will get an error, even if it is not used on the car, it must still be grounded. One can follow the tracks from the pin number on the wiring diagram to the inside of the unit and find the break.

Inside the unit are 3 X 8 bit shift registers. Three chips linked together to form a 24 bit register. A shift register reads and converts a parallel number to a serial one. Find the data sheet and you can see which legs are the inputs. Each sensor wire connects to the unit, then inside goes through a diode and then resistor and then to the shift register. There is also a small amount of other circuitry in the unit that takes a signal from the Light control unit to check for faulty bulbs.

1994 E34 540iA Glacier Blue
1997 E39 540iA Aspen Silver

Capetown South Africa
"The Mother City"

• False alarm Check Control messages - rick540 2007-07-21 14:50:27 (196 views)
  • low battery voltage & failing ignition switches have been known to cause - Q 2007-07-21 18:13:48 (114 views)
    • The fix and how the Check Control works. (longish) (pic) (url) - rick540 2007-07-21 20:07:18 (523 views)
      • Re: The fix and how the Check Control works. (longish) - Jerome 2007-07-21 22:08:12 (199 views)
        • Re: The fix and how the Check Control works. (longish) - rick540 2007-07-22 04:45:38 (147 views)
          • Re: The fix and how the Check Control works. (longish) - Jerome 2007-07-22 11:39:16 (131 views)