Battery Regulation

Phillip Diagnostician Anchorage, Alaska Posted   Latest  
Question
Electrical
2007 Audi Q7 Premium 3.6L (BHK) 6-spd (0AT)
03041 Energy Management Active & 02254 Interface To Generator

So this vehicle came in with a broken brake line and one of the issues I noticed was that the vehicle would loose electrical power. But still stayed running. This problem only seems to happen on a cold start. When checking for charging voltage found that I only had 9 volts. This problem only happened once so I informed the front counter and repaired the brake line like a week later when the parts arrived. The problem returned again when trying to pull the vehicle out the shop. So me being me said I refuse to drive the vehicle unless I know the alternator is charging. I pulled codes in the battery regulation module. They were 03041-Energy Management active & 02254-Interface To Generator (No signal). When I checked the PID's I did find a a PID for interface to alternator not OK but generator PID said OK. The alternator at that time was outputting 14.2 volts and the battery was getting 14.1 volts.(battery is located under the driver seat and is not easily accessible so I used the jump post inside the engine bay to check the battery) Also another thing I noticed if I performed a snap throttle the alternator would start charging. So I let the vehicle sit over night and next morning pulled out the PICO scope. On the back of the alternator is the battery + heavy gauge wire and a 2 pin connector with 1 wiring coming out that is a LIN-BUS to the energy management control module. So during the no charge problem the LIN-BUS at the alternator is showing 0-charging voltage square wave and is a pull up. I never loose the signal and the signal does not change when I disconnect the connector. This to me is saying the wiring from the alternator to the module is good. So my Question is what do those codes mean? Cause their literally no information I was able to find on alldata or prodemand. I am about ready to call an alternator on this thing and possibly a battery once I test it. 

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Joel Diagnostician
Soquel, California
Joel Default
   

with the Lin wire unplugged the alternator should produce about 14.1 volts , the regulator goes in default mode . if the alternator and regulator are working correctly.

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Phillip Diagnostician
Anchorage, Alaska
Phillip Default
 

Thank you that was very useful information.

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Mike Diagnostician
Toronto, Ontario
Mike Default
 

It's been a few years now since working for VW/Audi but IIRC on later models when the LIN signal between the module and generator is lost it will default to a fixed output voltage like Joel mentioned. I also seem to remember on some variants the Generator speed needs to be raised above a threshold before the regulator starts to supply a field current to begin charging.A blip of the throttle…

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Mike Diagnostician
Toronto, Ontario
Mike Default
   

Those codes are basically saying 1- The BEM has lost communication with the generator at some point ( which will not bring on a charging system warning light even when the comm fault is active) 2-The BEM is managing electrical load deactivation. This is because the BEM has deemed the battery to have reached a level of discharge which prompts the BEM to deactivate electrical loads in stages to…

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Phillip Diagnostician
Anchorage, Alaska
Phillip Default
 

I might be a a little confused. During normal operation instead of seeing 0- 12+ volts up on the LIN-BUS. I would see something like 0-2.5 volts or 0-5 volts signal on the LIN-BUS if the alternator is sending a response back to the BEM?

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Mike Diagnostician
Toronto, Ontario
Mike Default
   

Hi Phillip, If you need some help with getting an EWD for the vehicle I can assist. I have not come across recessive voltages of 5V/2.5V on a LIN bus in the past. Does the communication code clear or come back right away? It might be easiest to run a temporary overlay from the BEM module below the drivers seat to the generator to see if a proper operation is restored and the code can be…

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Phillip Diagnostician
Anchorage, Alaska
Phillip Default
 

I uploaded a picture. Somehow I deleted the PICO waveform so I only have a screen shoot. But with key on engine off .The LIN BUS sits at 0 volts and then is pulled up when the vehicle is running. This happens weather the connector is plugged into the alternator or disconnected from the alternator. Yes the code comes back once erased or as soon as the engine is started. I can get a diagram I just…

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Mike Diagnostician
Toronto, Ontario
Mike Default
 

That looks OK at a glance. With only the BEM and Generator on the bus with the connector unplugged I would expect to see a change in the pattern and a 'gap' where the generator's response should be to the BEM. If the signal remains unchanged whether plugged in/unplugged I think you are likely on the right track with a faulty generator.

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Phillip Diagnostician
Anchorage, Alaska
Phillip Default
 

I would agree and that is what I was thinking also to a degree. I was also theorizing that cause the alternator wasn't doing what it is supposed to be doing the BEM was constantly sending a signal to try and get the alternator to do something. Unless the the BEM is looking for voltage change rather then a signal on the LIN-BUS.

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Mike Diagnostician
Toronto, Ontario
Mike Default
 

Hi Phil, It looks like I am on a learning journey here as well. Digger a little deeper it looks like this setup with a BEM uses a protocol called BSD (Bit serial Data) vs the LIN protocol we are seeing with newer smart generators that communicate with the gateway module. I was looking a little more closely at your screenshot and although the voltage levels look correct communication looked…

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