Ianmac Posted January 7 Share Posted January 7 Im a new member. Have had an A4 (B9)for two years its well serviced and in good mechanical condition. With the start of the cold weather at switch on numerous warning lights appear some staying after engine starts. The car will run OK with no obvious driving problems Residual lights are usually Tyre pressure, cruise control ,abs, and engine warning. Battery is New, Resetting the fault codes using a diagnostic unit from my local garage works but the faults re appear. Any suggestions Quote Link to comment Share on other sites More sharing options...
Magnet Posted January 7 Share Posted January 7 Welcome to the forum John, and thanks for joining. Sorry to hear of your issue, and as I started to read your post ‘battery’ came straight to mind, as lower temperatures has adverse effects on its performance. Then I see you have fitted a new battery, so …..?? What I would now ask John:- Was the new battery match the correct specification for the car? Was it coded to the car? Was the alternator output checked? What make is the new battery? Kind regards, Gareth. Quote Link to comment Share on other sites More sharing options...
Ianmac Posted January 7 Author Share Posted January 7 Gareth I relaced the battery after the first experience of the fault indicator issue. The same logic as yourself as the battery was 6 yrs old The unit fitted is a VARTA of the correct spec for car with stop start rating. I did have it fitted by my local garage but I will need to check if it was coded. I cant find any info on the net as to why this is needed and what in fact the electronics do to need this. I have the old battery and fully charged it is sitting at 13.2 volts which indicates all cells are ok. My concern was a deterioration of the battery internal resistance ( Impedance affecting its decoupling properies across the + to - rails) regards John Quote Link to comment Share on other sites More sharing options...
Magnet Posted January 7 Share Posted January 7 Thanks John, Varta was/is the O.E. Supplier to VAG so that’s obviously great. Re. coding. The new battery needs to be coded to the car, so that the BCM recognises it and doesn’t treat charging conditions etc. exactly as it did with the old one. Well worth checking that that was done at the switch over point. Was the alternator output checked prior to changeover to ensure the alternator was increasing the charging to approx. 14.5+ volts? OK, the old battery may now be reading 13.2v in its fully charged condition, but static voltage is not that meaningful in isolation in these overall serviceability with our modern high demand vehicles. Apologies, but I’m not fully understanding your concern statement. Kind regards, Gareth. p.s. What were the symptoms that led you to get the original battery replaced? Quote Link to comment Share on other sites More sharing options...
Ianmac Posted January 7 Author Share Posted January 7 Gareth the battery was replaced after the first instance of the fault indicators appearing, this was based on my past experiences of battery performance being adversely affected by low temperatures plus the age of the battery. Unfortunately this was not the cure as the fault indicators are still appearing. The Internal resistance of a battery usually increases with age and shows up with a reduced terminal voltage as the current being drawn increases and is probably mostly apparent when using the starter motor. In the modern car the voltages/ currents flowing in the cables are not totally DC ,as Data signals are commonly used. These switch between two DC levels so if you looked at the voltage waveform on a scope you would see a series of pulses approx +-12v. As soon as one goes into digital its a different world as one is now dealing with very high frequencies not just DC. This can introduce unwanted AC signals on the DC power feed which can cause false triggering (Errors) in the car digital electronics . These are normally removed by decoupling circuits which in simple terms give the unwanted signal an easy route to / battery neg/ ground/ earth. The battery in its good low internal resistance condition is part of this process. The unwanted signals being AC as opposed to DC means one is looking at capacitance and inductance as well as resistance thus the name change to impedance . ( AC resistance ) I was trying to ensure false triggering was not the reason for my fault indicator issue Hope this helps John Quote Link to comment Share on other sites More sharing options...
Magnet Posted January 7 Share Posted January 7 Thanks John, Two questions still remain within the process of elimination:- Was the new battery coded to the car? Was the alternator output checked? Kind regards, Gareth. Quote Link to comment Share on other sites More sharing options...
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