I changed my alternator and battery they both test as good but my car wont charge the battery it keeps shutting down like the alternator is bad the horn is clicking and the airbag light comes on just...
Might be anything, but before going further I wish to check and clear three most common factors:
There are 3 most common reasons for the battery to drain.
You have to check these one by one.
A bad charging system.
Start the engine, and with a multimeter, or Volt/ Ohm meter, set at 20V DC, measure the voltage between terminal (+) at the battery, and a good ground. The reading should be 13.8 V to 14.2 V. If this is O.K then you have to check the battery.
Stop the engine and check the voltage between the (+) and (-) terminals of the battery. If the voltage is 12.6Volts than the battery is fully charged. If it is 12.45Volts the battery is 75% charged and so on. A bad battery is not able to hold the charge anymore, and need to be replaced with a new one.
The third reason is a phantom voltage leak.
This is a parasitic electrical drain on the battery, because a relay is sticking, a module is not shutting down, or there is a shorted diode in the alternator. To check this you need a bulb 12V 1 Amp, connected with two wires and two alligator clips. Disconnect the harness from the positive terminal of the battery, and connect the bulb in serial, with positive terminal of the battery, and with positive harness of the car. Make sure to create solid contacts with alligator clips. The car electrical system hates sparks, which you have to avoid. As soon as you connect the bulb, the system might sink up to one Amp of electricity. This happen because the modules and computer starts learning, but soon the current will decrease in milliamps. If not then you have parasitic electrical drain on the battery. In this case you have to remove and put back in place, one by one all fuses. If the light shut off then you have located the problem.
Oct 21, 2010 |
2000 Mercury Sable