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Randall C
Randall C, ASE Master Tech
Category: Jeep
Satisfied Customers: 12803
Experience:  ASE Master Tech, L1, Jeep owner, Shop owner
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I have a 1997 jeep wrangler tj. I've been having issues with

Customer Question

I have a 1997 jeep wrangler tj. I've been having issues with the alternator not charging the battery. After purchasing a new alternator and battery....the problem still exists...
Submitted: 1 year ago.
Category: Jeep
Expert:  Randall C replied 1 year ago.

Hello, sorry for the delay. Do you have a volt meter or testlight to check a couple things

Customer: replied 1 year ago.
I'm actually on the highway as we speak coming from work...but I tested the battery the new alternator the fuses and relays
Expert:  Randall C replied 1 year ago.

well, do you want me to send the answer as I am rather confident it is or ? have you checked main powerf eed to the alternator?

Customer: replied 1 year ago.
u can send the answer and I'll try it once I reach home. Thank u
Expert:  Randall C replied 1 year ago.

Its not an answer in which you can simply try, The charging system is 100% computer controlled, The alternator really does very little. The PCm controsl all of it,. In the shop, I have to say, in past 20 years? most all Dodge/jeeps with charging problme wind up being the PCM,.It is very very common for the PCM to fail and prevent charging, You changed the alt, battery tested etc so,, I am sitting on about 98% you have a bad PCM, You can easily do an online search about Jeep PCm controlled alternators and will see many posts on this

I have attached the wiring diagram, It shows the PCM in the link of the charging system. Below is direct from the Jeep manual

The charging system consists of:

  • Generator
  • Electronic Voltage Regulator (EVR) circuitry within the Powertrain Control Module (PCM)
  • Ignition switch (refer to Powertrain Management/Ignition Switch for information)
  • Battery (refer to Starting and Charging/Battery for information)
  • Battery temperature sensor
  • Generator Lamp (if equipped)
  • Check Gauges Lamp (if equipped)
  • Voltmeter (refer to Instrument Panel, Gauges and Warning Indicators/Instrument Panel/Voltmeter for more information)
  • Wiring harness and connections.

The charging system is turned on and off with the ignition switch. When the ignition switch is turned to the ON position, battery voltage from the powertrain control module (PCM) is supplied to the generator rotor to produce a magnetic field. This is done through one of the two field terminals at the rear of generator. On Jeep models of previous years, battery voltage to this field terminal was supplied from the ASD relay.

The amount of DC current produced by the generator is controlled by the EVR (field control) circuitry contained within the PCM. This circuitry is connected in series with the second rotor field terminal and ground.

Customer: replied 1 year ago.
OK..I will get back to you. Thank u
Expert:  Randall C replied 1 year ago.

Ok, There really is no testing for this, If you start testing at the back of the alternator, you run the risk of damaging the PCM even further. Its all about design and yes,, it has been a huge headache for many over the years,