Code 02254 & 003141
Okay vehicle came in originally for broken brake line, but notice that battery was weak and that when first start up sometimes vehicle would have no charging voltage. So all said and done customer had me look into it. Found 2 codes. 02254-Interface To Generator & 03041-Energy Management Active. The 03041 is just a battery saving feature that from my understanding. So I found out that when that alternator would not charge on start up, if you snapped the throttle or raised the RPM's alternator would charge. Also note that the battery was charged for half a day before I started diagnostics. In the battery regulation module pids, I found a pid for generator & generator interface. Generator interface pid reads not ok & gernerator pid reads ok. So I pulled the pico out and hooked up to the blue LIN-BUS wire. I had a like 500-600 mV key on engine off. With key on engine running signal rose to charging system voltage and was a square wave. I unplugged the connector from the alternator and had the same thing. From my understanding with key on I should have 12 volts on the LIN-BUS line and should be a pull down design. So I took a test light and jumped the LIN-BUS wire to 12 volts with the vehicle running and my generator interface pid then read ok. So I said to myself that alternator must be bad. I theorized that the alternator sends a 12 volt signal to the battery regulation module to let it know its okay. In turn the regulation module sends a pull down square wave signal back to control the alternator. Because the battery regulation module was not seeing the 12 volts from the alternator it was trying to wake it up with a square signal. So a month later leading to today I get an alternator and install it. And find the same problem. Code came back after installing alternator and have a generator interface pid reading not okay. So now I am lost and do not know what to do now. I thought I understood how the system works from the reading and videos I watched but clearly I have zero clue.
Was this alternator OEM or aftermarket. Reason I'm asking is because Audi uses different Lin numbers and frequencies when it comes to the voltage regulator.
Directly from Audi. This was a customer supplied part but it was un opened in a Audi box. Numbers on the back of the alternator did match.
Try reset terminal 30 on the BEM(battery energy manager control module ) disrupt the power supply at terminal 30. If this does not resolve the complaint, you probably have a faulty BEM.
Did you check for possible voltage drop on the B+ terminal on the alternator. also make sure power and ground is good to the BEM
Please Check Part Number of BEM - 4L 910 181 = Most Bad , 4L0 910 181 A = Most Good, but had about 5 of these with that Code.
I have Never had a Generator Fail without a Generator Pid = Fail, every (except one) Interface Gen. Failure was a bad BEM-Module.
Only once had a bad Wire - After bad Front Crash repaired somewhere.
Audi A6,A8 and Q7 all have this Problem regulary.
Very Old Capture of a A8 4E attached.
If memory serve me me, the Gateway J533 and ECM controls the alternator. The BEM looks at the electrons moving in and out of the battery. Look at J519 for battery load determination.
See if there are any output test from either J623 or J644 for the alternator.
Have you reset the Battery Management System as if the battery were replaced? Many BMS systems have an algorithm that assumes degradation of the battery over time. If a battery is replaced and the system not reset, the system behaves abnormally. Ideally, the battery would need to be of the same type. (Flooded / AGM) The DIN / CCA needs to be the same as well. This model seems a little old for this but it could have it.