E70 Voltage issue
 

I was attempting to jump an 07’ 4.8 I had my code reader hooked up at the time as I wanted to see if there were any pre-existing codes in the modules. I noticed with the jumpers hooked up and electrical donar vehicle running all I was seeing on my code reader as far as voltage was sub 12 volts 11.65 to be exact. I was surprised I didn’t see 13.5 plus. I jumped using the terminals under the hood. As I did not have a volt meter with me I was unable to confirm how much current was getting to the battery. Although after looking at the electrical diagram I don’t see any reason there shouldn’t be the 13 plus volts getting to the battery. Any reason there wouldn’t be 13 or so volts seen at or by the DME? I did check connections at the battery and connections tight and clean. I did attempt a start but engine turned over very slowly no start. Thinking IBS or poor ground perhaps? Thank you for any guidance.

Yes I agree this is strange. Well that said I bought it and will be reporting back with my findings.

Sub 12 volts I don't think is uncommon before startup. However, at least 13v is important to achieve once the vehicle is started. Im guessing maybe the donar vehicle has a smaller battery, no?

It was another X5 E53 to be exact so another group 49 battery. I don't think the alternator is coming on line as I was able to start but only runs for 3-5 seconds before shutting down and lots of error codes.. This is a new vehicle to us and has sat for over a year. I finally have it in my car port so will get a better chance to check fuses, connections etc. Will report as I go through the systems. Thank you

Today I was able to confirm for the 5 seconds the car would run the alternator was not charging. Now onto finding out whats at fault, alternator or DME.. Lots of codes thrown after the 5 second run. One of the more notable was - Alternator not seen. Voltage regulator??

pull the alternator and replace the voltage regulator piece. mine works great now. prior to this we threw codes and transmission went i to limp mode.

I agree. I just ordered one.

Also going to pickup a pair of the Blue relays for the DME. I don't mid spares..

What is so special about the blue relays? And speaking about dme relays, which are responsible for the communication with the valvetronic computer?

DME relays were/are a known failure point, especially for my old Porsche. Just though I would cover off another potential culprit. The relays are blue in colour and located by the DME. DME talks to quit a few components so keeping a close eye on the thing. Spent quite a bit of time today checking all the fuses (Got to love the front fuse box..) All fuses were good. My BIG concern is this thing sat for well over a year and owner reports it running when parked due to rear bags collapsed and pump not operational (Confirmed pump not working and main 40A fuse blows - Looking for a replacement ;) so somewhere over that time something went off the rails. I guess its possible the regulator could have gone faulty over that time frame. Or that was another reason it was parked.