Jeep Liberty Charging Voltage High?

[LiberySport02]

I recently replaced the alternator and battery in my 02 Jeep Liberty. With the vehicle running, I am measuring between 14.8 to 15.6 volts coming out of the alternator. I get the same measurement out of the alternator and when measuring at the battery posts. When I turn off the vehicle and measure at the battery posts the meter reads around 13;volts. Is the charging system voltage too high and to be concerned of? I have the factory service manuals, so I learned the voltage regulator is in the PCM. PCM seems grounded well per checks I did with my meter. No trouble codes are being triggered. The field circuit connections from PCM to alternator appear good. If the voltage too high, I'm skeptical about blaming the PCM since I'm not having any other issues. When I recently changed the alternator & battery it was due to the battery would not fully charge. I really appreciate if someone has some has some experience or knowledge they can share on this issue!

 

[turblediesel]

Haven't had alternator problems with my jeep yet but I'm on my third alternator replacement fordwise. First seized, second no-charge, third over-charge. Quality of rebuilts seems to have taken a dive.

 

[LiberySport02]

I believe the alternator is OK because I was reading the same high voltage prior to replacing it. I'm wondering if it could something besides the PCM which controls the output of the alternator. Thank you for your response!

 

[JasonJ]

I believe the alternator is OK because I was reading the same high voltage prior to replacing it. I'm wondering if it could something besides the PCM which controls the output of the alternator. Thank you for your response!

The voltage regulator controls the output of the alternator.. hence it's name. And as you said, it's located as a circuit within the PCM.

15.6v is high... anything over 15v is considered a high charging situation, but I'd defer to the SM for the Chrysler specs on what they consider "normal".

 

[Billwill]

The PCM detects the charging voltage somewhere and adjusts the voltage on the field coil accordingly using Pulse Width Modulation (PWM) which are ON/OFF pulses of voltage changing in duration of pulse depending on the required voltage output needed.

I had major problems on my Export 2002 CRD caused by wiring harness damage caused by a front bumper bashing.....with a voltmeter plugged into the front cigar lighter so that I could monitor the voltage while driving I would find that if I did some action such as turning the front wipers ON the voltage would rise to +17 volts at which time there would be a "ping" and the Jeep would grind to a halt. So after re-starting I would have to avoid using the wipers....pity I was on a long trip and it was pouring with rain!
I ended up tracing about 7 wires in the harness up front that were semi-shorting to ground so I had to replace them all....by this time the battery had boiled itself to destruction.

I would suggest that you check all the connections are clean and tight ie. the battery terminals, the negative lead going to chassis and the engine grounding strips grounding the engine to chassis.

The early KJs have a Battery temperature Sensor located under the battery which helps the PCM adjust the voltage slightly according to temperature...if this fails it sets the same red Battery Icon as a charging problem does. Possibly this sensor is not working properly...you can remove it after removing the battery....if your Jeep has this sensor fitted. Measure the resistance of the sensor at room temperature....should be around
2,000 Ohms if I remember correctly. Warm up the sensor on a light bulb and the resistance should drop down to about 30 Ohms if it is working.
I had a problem with the one side of this sensor....supposed to go to ground....had its ground go missing somewhere so I added my own ground. I also had to ground the metal casing of my PCM....ECM on the CRD...down to chassis to finally resolve all my issues.

You can get the Jeep KJ Service Manuals for your year model...except 2005...here.
This includes Theory of Operations and the wiring diagrams:
http://www.colorado4wheel.com/manuals/Jeep/KJ

 

[LibertyTC]

Great write up Bill!! ^^ This is the Battery Temperature Sensor Location
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REMOVAL
From FSM:
The battery temperature sensor is located under the vehicle battery and is attached to a mounting hole on battery tray.
(1) Remove battery.
(2) Disconnect sensor pigtail harness from engine wire harness electrical connector.
(3) Pry sensor straight up from battery tray mounting hole.
INSTALLATION
The battery temperature sensor is located under vehicle battery and is attached to a mounting hole on the battery tray.
(1) Feed pigtail harness through hole in top of battery tray and press sensor into top of battery tray.
(2) Connect pigtail harness.