I have a 2020 Jeep Wrangler Unlimited Sahara with the 2.0L turbo eTorque system and about 135,000 miles. I’m dealing with an intermittent 12V charging problem and I’m trying to figure out whether the issue is the 12V battery/IBS, belt tensioner, MGU, PPU/DC-DC converter, or a wiring/ground problem.
The issue started with a Battery Saver Mode message and check engine light while driving.
My 12V battery is about 4–5 years old. During my first testing I got approximately 11.9–12.0V engine off and only around 10.5–11.0V while the engine was running. Raising RPM did not initially bring charging voltage back.
I then externally charged the 12V battery. On another start the Jeep began charging normally at approximately 14.0–14.2V, showing that the system is capable of producing charging voltage.
The problem is that charging is intermittent. While the Jeep is running, voltage will sometimes fall into the 11–12V range, then rise back into the 13–14.2V range, sometimes without me touching the accelerator. Turning on electrical loads such as the headlights has sometimes caused the voltage to rise back toward 14V.
I also pulled a U0100 – Lost Communication With ECM/PCM code. Freeze-frame data showed ECU voltage at 11.425V. The same freeze frame showed clearly invalid readings such as 419°F coolant temperature and 16,384 RPM, so I suspect the communication code may have occurred because of the low system voltage.
I have also noticed an unusual mechanical/load noise from the eTorque belt drive. When the noise happens, the two tensioner arms visibly move/bounce, and I have noticed small RPM changes and charging-voltage changes at about the same time. The belt itself stays seated and feels very tight with the engine off with no obvious slack.
I checked the main belt visually and it is intact. I have also checked several fuses and previously measured approximately 11.7V at the N1/N8 PDC studs during a low-voltage condition.
One separate event occurred while the Jeep was connected to another running vehicle with jumper cables. I revved the Jeep and heard a louder banging/noise, so I shut it down. That was separate from the first time the Jeep successfully charged at 14.2V.
I am planning to have the 12V battery properly load/conductance tested, but I do not want to replace expensive eTorque parts without confirming the cause.
My main questions are:
* Does the tensioner movement in the video look excessive?
* Could the MGU be repeatedly loading/unloading the belt and causing the tensioner movement?
* What tests would you perform to separate a bad tensioner/belt-drive problem from an MGU or PPU/DC-DC charging problem?
* What live data or voltage-drop tests would you check before condemning the MGU or PPU?
I can provide additional voltage readings and videos if needed.
The issue started with a Battery Saver Mode message and check engine light while driving.
My 12V battery is about 4–5 years old. During my first testing I got approximately 11.9–12.0V engine off and only around 10.5–11.0V while the engine was running. Raising RPM did not initially bring charging voltage back.
I then externally charged the 12V battery. On another start the Jeep began charging normally at approximately 14.0–14.2V, showing that the system is capable of producing charging voltage.
The problem is that charging is intermittent. While the Jeep is running, voltage will sometimes fall into the 11–12V range, then rise back into the 13–14.2V range, sometimes without me touching the accelerator. Turning on electrical loads such as the headlights has sometimes caused the voltage to rise back toward 14V.
I also pulled a U0100 – Lost Communication With ECM/PCM code. Freeze-frame data showed ECU voltage at 11.425V. The same freeze frame showed clearly invalid readings such as 419°F coolant temperature and 16,384 RPM, so I suspect the communication code may have occurred because of the low system voltage.
I have also noticed an unusual mechanical/load noise from the eTorque belt drive. When the noise happens, the two tensioner arms visibly move/bounce, and I have noticed small RPM changes and charging-voltage changes at about the same time. The belt itself stays seated and feels very tight with the engine off with no obvious slack.
I checked the main belt visually and it is intact. I have also checked several fuses and previously measured approximately 11.7V at the N1/N8 PDC studs during a low-voltage condition.
One separate event occurred while the Jeep was connected to another running vehicle with jumper cables. I revved the Jeep and heard a louder banging/noise, so I shut it down. That was separate from the first time the Jeep successfully charged at 14.2V.
I am planning to have the 12V battery properly load/conductance tested, but I do not want to replace expensive eTorque parts without confirming the cause.
My main questions are:
* Does the tensioner movement in the video look excessive?
* Could the MGU be repeatedly loading/unloading the belt and causing the tensioner movement?
* What tests would you perform to separate a bad tensioner/belt-drive problem from an MGU or PPU/DC-DC charging problem?
* What live data or voltage-drop tests would you check before condemning the MGU or PPU?
I can provide additional voltage readings and videos if needed.
Sep 17, 2026 at 9:14 AM
