A4 ccm module

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Hi,

My mother’s a4 estate has had some electrics stop working.

I had an issue a year ago where passenger door wouldn’t unlock, it was the window regulator changed that and all was fine.

This year the drivers door stopped working on the central locking but the other three and boot still work and the electric windows and mirrors stopped working on every door.

I changed the regulator but that didn’t work, I read that it was likely the ccm I’ve bought one off eBay and tried it today but it wouldn’t work at all, I couldn’t even sync the keys again. Usually I just do this by pressing the unlock button and holding it while I turn the ignition on for a few seconds turn it back off then release the button but nothing.

Is there something I’m missing with regards to syncing the keys and is there anything else that may be causing the issue?

My next step would be to start looking for a broken cable probably in door shut area
 
My first reply on here so I’d better make an effort...

So I’m not 100% sure but I think this is still an issue with the driver door control module or the wiring/connectors which lead to it from the CCM

From the description it’s sounds like the CCM was working as intended with all functions other than those to do with the driver door control module whilst none of the functions of the driver door control module are working

Did the old CCM have any signs of rust or water damage?

Do you have a VAG compatible scanner? If there’s any codes on the CCM they’d be useful

The CCM communicates with the door control modules via a CAN bus. The CAN bus comms was working on the old CCM as the other doors windows etc. were working. To make it easier to narrow down the fault it make sense to use the old CCM and check it was working as before (windows on other doors etc)

Assuming that the replacement door control module works and is compatible then I think looking at the wiring between that and the CCM could be the next place to look for the problem. (It should be possible to test the operation of the CCM and driver door module without relying on the connection between both, but it’s fiddly and risks frying boards)

Wiring diagram for CCM and door modules found here:

The forward most connector on the door control module should have two fat wires and a number of smaller wires. The wires of interest are the two 12V from the fuses, the fat brown GND wire. The CAN high and CAN low and what is referred to as convenience which I assume is Convenience CAN bus GND ref

Check the power wires have 12V (check fuses if not)
Check the GND wire has low resistance to chassis gnd
Disconnect battery and measure resistance between can high and can low. Shouldn’t be short circuit or open circuit but should be (50 and 150??)
Measure resistance between can high and can gnd. Then can low and can gnd. Both readings should be k ohms
The electrical continuity of the CAN wires between the door module connector and the CCM can be tested
The three power supply lines were tested whilst the battery was still connected

If these wires show problems look at the state of these wires where they cross from door to chassis in the rubber sleeve (insulation and wires get damaged in this area) and check the 20 pin black connector here also (sometimes far too much grease in the connector electrical insulated the contacts)

If these 3 power wires and 3 can wires appear to function correctly and the fault still exists then a problem with either module should be looked into. Possibly configuration, firmware corruption, incompatibility or hardware damage

As to why you key doesn’t work on the remote I think it is because some sort of security programming is needed to link the used CCM to the car. Can someone confirm? The antenna for the remote locking is controlled by the CCM which passes the data to the dashboard control which has the immobiliser. The A4 B6 SSP (which is worth reading) describes this as well as giving a decent overview of the electrical system

Well I’ve waffled on enough. Best of luck
 
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