Hey guys, I know this has been beat like a dead horse because it’s a JK with electrical problems but I’m hoping maybe someone has a different idea because I’m all out. 😅

Started with a dead battery, replaced the battery, dead again, replaced the alternator, dead again, replaced the battery and the alternator with known good ones, dead again, replaced the PCM thanks to the guys at WranglerFix, alternator is showing good, but doesn’t *seem* to be charging the battery (I haven’t driven it since I put the pcm in, but battery isn’t kicking up in voltage when it’s running). I checked all of the grounds, they’re solid but I cleaned them anyways and added some dielectric grease where there were more than 2 connectors on a post. Put it on a trickle charger last night. Battery charged to full according to the trickle charger. Take the charger off, battery showing 12.78 volts. Voltage drop is >1v (from 12.78 down as far as 11.4).

Any ideas on where to run next?

I appreciate y’all immensely!

 

Realized I ran the voltage drop test wrong, just did it again and it’s got a drop of .08.

 

0.08VDC is not a problem for sure. So do you still think there is a problem somewhere? Let us know!!

 

Definitely still a problem somewhere. Battery still isn’t being charged by the alternator. Figured TIPM testing is next but not sure how to go about that.

 

Do you have any fault codes? You'll need to have an OBD2 reader and an associated app.

What year is your JK? What engine? Likely either the 3.8L or the 3.6L, but there are others. The charging system is quite different between 2007-2011 and 2012+, and between different engines within the same years. The diesel version, for example, is very different. But those are rare in North America.

 

2015 JK Willy’s wheeler, 3.6L, only fault codes seem to be low voltage related. B210A, B210D, P2504, U0121, U0184, U0168, P0693.

Also, checked the IOD fuse, it is good.

 

OK. That helps. The common threads through those fault codes are the PCM and the TIPM.

Here's the wiring diagram:


As you can see, the TIPM doesn't play much of a role in the charging system except for fuse M28. So check that first. Check to make sure power is getting to the fuse too. Check all of the above wiring the best you can to eliminate any other possibility of broken or shorted wires.

If that's not it, things get a bit more complicated. Here's the theory of operation for the charging system:






For DTC P2504-Charging System Output High.

The Electronic Voltage Regulation (EVR) system maintains the system voltage at a desired level by turning the Pulse Width Modulated (PWM) Alternator Field Control circuit (A) on and off. When the Alternator field is turned on, the system voltage increases. When the Alternator field is turned off, the system voltage slowly drops. The rate at which this happens is dependent upon the existing electrical loads, ambient under hood temperature, and the engine RPM. A constant system voltage (B,C,D) can be maintained only when the Alternator field is switched on and off at a duty cycle that very accurately emulates the existing electrical loads given the existing ambient under hood temperature and engine RPM.

During normal operation, the voltage reading at the Alternator output stud will be very close to the target charging voltage viewed on the scan tool. This is the system voltage and is sensed by the Powertrain Control Module (PCM) through the Fused B+ circuit (B). With the Alternator connector plugged in, the voltage reading on the Alternator Sense circuit will be approximately 3.5 volts less than the voltage at the Alternator output stud due the resistor inside the Alternator. This is the Alternator Sense (E) input to the PCM. These two voltage sense inputs are used and compared during the different diagnostics performed on the EVR System by the PCM.

Diagnostic Mode: The PCM will run the Alternator Voltage High diagnostic to determine that the Alternator voltage sense (E) is higher than the system voltage (B,C,D) by a calibrated amount. It will give a rapid warning that the Alternator output terminal, Alternator output wiring or the fuse/fuse link in this output wiring had conductivity problems. This can include permanent or intermittent disconnections, or excessive resistance in the wiring caused by either corrosion or a loose connection.

Possible Causes:
OPEN OR HIGH RESISTANCE BETWEEN THE ALTERNATOR B+ TERMINAL AND THE TIPM B+ TERMINAL
RESISTANCE IN THE FUSED B+ CIRCUIT BETWEEN THE TIPM AND THE PCM
TOTALLY INTEGRATED POWER MODULE
ALTERNATOR
POWERTRAIN CONTROL MODULE (PCM)

From here, there are specific steps that need to be done to isolate each possible cause. Without going through each step in detail, here are a few highlights you might try. You can use your OBD2 reader with an app like JSCAN or Alfaobd to find the parameters.

With the scan tool, navigate to data display and monitor the target charging voltage. Measure the voltage at the Alternator output stud. Should be within 0.2VDC of each other. If not, replace the alternator.

Measure the voltage on the Fused B+ circuit at the TIPM B+ terminal and at the alternator stud. Should be within 0.2VDC of each other. If not, check the wiring. Repeat following the wiring from the battery to the alternator.

If everything looks good across all wiring, the likely suspect is the PCM.

Hope this helps!

 

Awe man incredible! Thank you so so much. I’ll run through that today and keep you posted.