Looking for a member with an 06 TJ and voltmeter

NskLJ

TJ Addict
Supporting Member
Joined
Oct 19, 2021
Messages
2,036
Location
Long Beach
Backstory I was driving home from a week in Colorado, I had smelled the battery off and on during the week. I was running lead acid. When I was coming through northern Utah the battery smell proceeded to get worse I checked the charging system at one gas stop and got 14.9 volts. I installed a AGM battery in St George so I didn’t have an issue driving through the California Desert. I contacted Wranglerfix he thought the voltage was a little high also. I installed my old PCM that has the transmission communication issue and have he same charging voltage. (Never had any charging issues with this PCM) I am looking for someone that can back probe the alternator field circuit while running to give me field voltage vs charging voltage and base battery voltage. I have added a few picture of what I’m looking for. Does anyone have any information on the battery temp sensor, it is not in the wiring diagram. I assume just a thermistor going to the PCM?
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Last edited:
From the FSM:
The PCM sends 5 volts to the sensor and is
grounded through the sensor return line. As temperature
increases, resistance in the sensor decreases
and the detection voltage at the PCM increases.
 
Also, my '06 does not have a battery temp sensor.

I can check my charging voltage tomorrow, but I'm pretty sure it's never been above 14 V.
 
From the FSM:
The PCM sends 5 volts to the sensor and is
grounded through the sensor return line. As temperature
increases, resistance in the sensor decreases
and the detection voltage at the PCM increases.

I figured it would just be a thermistor but didn’t see it in he manual other then the connector in the harness drawing in the electrical section. Probably same values as the IAT.
 
Also, my '06 does not have a battery temp sensor.

I can check my charging voltage tomorrow, but I'm pretty sure it's never been above 14 V.

If you would I would appreciate it and if you can check the field voltage also. What is odd it’s just a little high and my other PCM has the same readings. I would expect it to fail on or off. Good to know on the sensor also, thanks.
 
After sitting overrnight, battery voltage was 12.67V and, upon startup, charging voltage at the battery was 13.60V.

I don't have any probes that will backprobe the field voltage.

Have you tried unplugging the battery temp sensor? It seems to be hit or miss as to whether one was installed at the factory, so I wonder what the PCM does when it's not there. My guess is it was installed in Jeeps delivered to northern states, but I have nothing to back that up.
 
After sitting overrnight, battery voltage was 12.67V and, upon startup, charging voltage at the battery was 13.60V.

I don't have any probes that will backprobe the field voltage.

Have you tried unplugging the battery temp sensor? It seems to be hit or miss as to whether one was installed at the factory, so I wonder what the PCM does when it's not there. My guess is it was installed in Jeeps delivered to northern states, but I have nothing to back that up.

I will pull the battery and check for the sensor. A paper clip would work for back probing if you can get in there. Thank you for checking this. This will be a challenge to isolate the issue.