Why does the battery light come on on my 1999 Mazda Miata automatic 135K miles about 15 seconds after starting. I simultaneously replaced the alternator Bosch remanufactured and battery?

Answer 1

There could be several possible causes, so the issue should be checked out by someone who knows what s/he is doing. Onepossible cause could be related to the primary/high idle speed settings. Most vehicles are programmed to hold the fuel system idle speed setting at a slightly higher RPM[revolutions per second] when the engine is first started, to prevent rough idle, or a "cold stall," and some also have a choke, and/or other method of providing a "richer" mixtureduring this time. This rich, high idle settting provides resistance to stalling until the combustion chamber becomes warm enough for the engine to idle smoothly, which for most well tuned engines is just a few seconds. After this time, the idle setting should return to the lower, normal [warm engine] idle speed setting. An alternator must turn at a certain minimum RPM to generate enough output to charge the battery, and to prevent the warning [idiot] light from turning on. IF the normal idle speed setting is too low when your engine returns to the "normal" idle speed, then the idle RPM may be too low to cause the idiot light to turn off. Again, there are several possible causes, so have your entire charging system checked out by someone who knows what they are doing. Most mainstream auto parts chain stores [for example, Advance, Autozone, O'Rielly] have the diagonostic/testing equipment to test charging systems, and they do it for FREE.