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I have a recently purchased 2019 GLS 450 52k miles. The car had the red battery light come on intermittently which led to the car dying on the road. I was able to jump the car and get it home, but the current limiter somehow fried after I boosted the car. The car would not start after this (loud click and nothing else). I replaced the current limiter (under carpet of front passenger seat) and alternator after it tested bad. Also changed the starter and put in 2 new batteries. The car now starts and runs great, no lights and seems to charge the battery well but I am getting the U012087 code on my launch reader which is shows that communication between the starter or alternator has a malfunction. The wires seem to be in good condition and I have checked the grounds that I found so I'm uncertain what may be causing this code or how to correct it.
Also, under normal operation, the current limiter is also getting too hot to touch on the battery connection side, and I'm not sure if this is normal or related to the communication issue.
the current limiter is also getting too hot to touch on the battery connection side, and I'm not sure if this is normal
I doubt it's normal. That kind of heat can damage the battery.
Heat is usually caused by a high(er) resistance connection. Make sure the connection to the battery is clean and tight. It looks like there may be a connection between the battery clamp and the input to the limiter, too, that could be loose or dirty.
Additionally, it should only get hot when there is a lot of current being drawn. What's drawing all that current? When the engine is running, there shouldn't be much current flowing into or out of the battery.
1 - Because of initial heating of the current limiter the cables, screws, etc could be with some carbon or oxide, may you clean and verify the torque for the screws.
2 - The Fault Code may be related with the Digital Lin communication between Alternator and the engine ECU. If your new alternator is not original you may check the relay for compatibility and also the connector.
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