HELP!
I have a completely stock 2005 TJ with a 4.0L engine and an automatic transmission. I replaced the battery in January and just replaced the alternator a few days ago, but the check gauges light is still on. Changing the alternator didn’t solve the problem. I watched the technician at Advanced Auto test the new alternator, and it checked out fine. At idle, the alternator’s output is 11.6 volts with no accessories on, according to my multimeter, and my scan tool shows the same reading at 2000 RPM.
There are no error codes from the ECU. Is the alternator controlled by the ECU? The ECU was replaced a few years ago. I also noticed that the brake fluid level light came on, even though the fluid is full. I initially dismissed it as not a big issue, but now I’m concerned the ECU might be failing.
Any help would be greatly appreciated.
First thing I would do is confirm the positive battery cable and all the ground wires/cables have a good connection.
A 2005’s field wires consist of a BR/BK wire running directly to ground at G105 and a BR/DG wire (Generator Source) running to the PCM at C2 pin 19.
As mentioned before battery should be good and fully charged(12.6v is a fully charged battery).
Best way to check is with a carbon pile tester. The Quick and dirty way hook your meter to the battery turn the ignition to run battery voltage should not drop below 12v ideally. When you start it voltage should not drop below 9.6v
If it fails the quick test it needs to be tested with a proper tester.
autozone said 11.6v was OK?
Lets start simple easy, engine off check and record -
voltage at battery,
voltage at alternator.
Start engine repeat.
V at battery.
V at alt.
you did use scanner to check codes?
Thank you for the response
Battery cable are clean and tight
I checked for codes with a scanner (Innova 6100P)
Engine off
Voltage at battery 12.12v
Voltage at alternator lug 12.11v
Engine at idle - no accessories on
Voltage at batter 11.66v
Voltage at alternator lug 11.66v
Can anyone shed some light on whether or not the ECU controls the alternator?
Thanks
The alternator’s voltage regulator is contained within the PCM, yes.
Your readings point toward the Jeep running entirely on the battery, the alternator is not charging. You should be getting a fault code or two pertaining to the charging system, though the less than 50% charge battery may be causing the PCM to not store any. Assuming the battery cable connections at both ends of the cables are clean and tight, you should probably take a look at the two field wires and their connections running between the alternator and PCM (the two smaller wires connected to the alternator, not the thick red one).
Yes Chrysler has put the voltage regulator in the PCM in their line of vehicles since late 89 or 1991 I’m having issues also changed PCM first cause I bought one from Wrangler fix few years back on another issue, never needed it then but alternator was still bad so bought another alternator but it’s not working either unless the new one is bad that can happen cause I just bought a cheap one. I guess I’m gonna try the other PCM just in case they both went bad these electrical issues can get crazy sometimes I’ve already cleaned the grounds up from the one in far back left just past dip stick it’s a 05 wrangler Rubicon 4.0 but was getting good ground before to plug going in the back before just checking everything ground I can learn about my question is can the PCM have a bad ground going to it besides checking the plugs cause I have 4 plugs and I think it’s the far right plug I forget the color mark