R2D2 Posted December 20, 2012 Report Share Posted December 20, 2012 My battery light has been coming on for about 30 seconds after starting my car up lately (it then goes out). I replaced the alternator last year so i can only assume that my battery isnt holding full charge any more, and the light goes out when the alternator tops up the charge on startup? I measured it with a multimeter after having stood for a day and it read 11.8V, am i right in thinking it should be more like 12.5V off load? Link to comment Share on other sites More sharing options...
B0B Posted December 20, 2012 Report Share Posted December 20, 2012 Could it be your serpentine belt slipping? Link to comment Share on other sites More sharing options...
R2D2 Posted December 20, 2012 Author Report Share Posted December 20, 2012 Could it be your serpentine belt slipping? No i dont think so, id hear it. I had it off when replacing the alternator as well and it seemed in good nick. Link to comment Share on other sites More sharing options...
R2D2 Posted December 20, 2012 Author Report Share Posted December 20, 2012 Does the battery light come on as soon as charge starts being sent by the alternator, or does it come on when the battery is below a certain voltage? Link to comment Share on other sites More sharing options...
marc l Posted December 20, 2012 Report Share Posted December 20, 2012 What's the tension like of the belt? That battery light means charging system Link to comment Share on other sites More sharing options...
R2D2 Posted December 20, 2012 Author Report Share Posted December 20, 2012 What's the tension like of the belt? That battery light means charging system Yeah i know that but i wondered specifically what causes the light to come on, is it voltage level across the battery terminals or is it the current level thats being drawn by the battery? Tension on the belt is fine. Link to comment Share on other sites More sharing options...
R2D2 Posted December 20, 2012 Author Report Share Posted December 20, 2012 (edited) Looking at the wiring diagram it would seem that wire X6524 would be the culprit. It must be dropping to 0V meaning that theres a 12V drop across the battery light causing it to turn on. Question is, what causes X6524 to drop (i believe its an ecu line)? EDIT: Actually i guess it could be the other way round and the voltage at X11175/X10016 is dropping below a threshold due to 12V battery rail being low causing the voltage drop across the battery light in the other direction. This would indicate that the battery light is related to the battery voltage level and not current drawn. Edited December 20, 2012 by R2D2 Link to comment Share on other sites More sharing options...
R2D2 Posted December 22, 2012 Author Report Share Posted December 22, 2012 Anyone? Link to comment Share on other sites More sharing options...
Rich_D Posted December 22, 2012 Report Share Posted December 22, 2012 anything below 12v with the engine off means the battery is goosed Link to comment Share on other sites More sharing options...
R2D2 Posted December 22, 2012 Author Report Share Posted December 22, 2012 Ta. Link to comment Share on other sites More sharing options...
ian332isport Posted December 22, 2012 Report Share Posted December 22, 2012 Yeah i know that but i wondered specifically what causes the light to come on, is it voltage level across the battery terminals or is it the current level thats being drawn by the battery? Alternator Compact alternator with multifunction controller (MFR)The alternator with multifunction controller features only one threaded pin for the terminal connection B+ (terminal 30). The connection D+ (terminal 61 E) is located in the black connector (2-pin or 3-pin depending on version) at the alternator. The terminal 15 connection is also located in this connector for voltage supply of the controller. In some models the load status of the alternator is signalled to the engine management. Compact alternator with multifunction controller (MFR) and start load responseThe alternator with multifunction controller (MFR) and start-load response does not differ externally from the alternator without the start-load response function. The difference only concerns the time limitation of the rated current during the start procedure. Start load response function:This function is intended to shorten the engine starting procedure particularly at low ambient temperatures. The task of the function is to eliminate a braking torque acting on the engine as the result of full excitation and current output. As a result, during the first few seconds the load current is limited to 0 A in order to achieve the full power output in the following few seconds increasing at a rate of 10 A per second. Multifunction controller:In the case of the multifunction controller, the battery charge indicator lamp is activated by means of an electronic switch integrated in the controller. The controller measures the voltage difference of terminal 30 and terminal 15 internally and switches terminated 61 E to ground in the case of fault. The indicator lamp lights up. Fault detection with multifunction controller with/without start load response:Failure of the belt drive (Ualternator = Uterminal 15 / no phase signal)no charge due to a fault (Ualternator = Uterminal 15)Interruption in excitation circuitOvervoltage by a defective, conductive controller output stage (Ualternator > Usetpoint)Break in charge line (Ualternator - Uterminal 15 >= 3 V +/- 0.5 V) Link to comment Share on other sites More sharing options...
Daz 330 Cs Posted December 22, 2012 Report Share Posted December 22, 2012 Get the battery checked out before you spend £££ and replace anything. Link to comment Share on other sites More sharing options...
