jeep wont charge but alternator isnt bad
changed aternator wont charge traced all the wires out none seemed to be broken is there a fusable link in the electrical system
The Jeep Grand Cherokee was redesigned for the 1999 model year; the 2000 models have minimal changes. This model is also known as Jeep WJ.
Looks like the field coil of the alternator isn't getting power.
There are 3 wires attached to the alternator. One is a big fat wire that goes to the battery, this is the alternator output. The other two wires feed power to the field coil.
You can check if the field coil is powered by connecting a multimeter to the terminals of the field coil, and starting the engine. Be careful to avoid getting caught by the alternator belt! With the engine running, there should be voltage across the terminals. Turn on the headlights to put some load on the battery, the voltage on the field coil should rise slightly.
If you don't see voltage on the field coil terminals, you might have a blown fuse. The field coil is powered by a box called Powertrain Control Module, and there are 3 fuses that might be of interest, numbered 6, 19, and 26 according to the schematic (see below). If these are all good, then you need to check the wiring between the PCM and the alternator, or the PCM itself may have a problem.
Another possibility is a bad Battery Temperature Sensor. If this sensor tells the PCM that the battery is too hot, the PCM might refuse to power the field coil 'cause it thinks bad things might happen if the alternator tries to charge an overheated battery.
I have exactly the same problem with my wife's grand Cherokee, if your alternator and battery are good and all connections are good then it's the voltage regulator in the computer that is bad, this is what is wrong with my wife's jeep, I'm going to fit an external voltage regulator to the body of the car, I'm going to splice the cables from the ones on the rear of the alternator to the voltage regulator which instead of the computer controlling the voltage the alternator kicks out, it will be the external voltage regulator that controls the alternator power output, this is all you need to do to fix your charge problem, I'm going to order a voltage regulator when I get home.
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