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Possible cause for charging system voltage spikes
Posted to Technical Discussion Forum on 1/17/2024 22 Replies

After more than 30 years in the auto repair business every day I found new (hard to solve) stuff...

Trying to make a long story short:

Received car because electric steering system check light going ON and hard steering, when driving through hard potholes. Sometimes.

Found on EPS "overvoltage" fault code. Interesting fact: despite car having about 50 electronic modules, just EPS "fells" it. Probably because it's power wired directly to near alternator output.

Checking charging voltage in the alternator output wire is possible to see voltage spike, in the moment of the (hard to reproduce) problem. With oscilloscope, because it is just a fast spike.

Car is AGM battery equiped. Then system charges battery up to about 15 volts. EPS will set overvoltage codes if voltage feed is over 17 volts.

In this case voltage spike goes to 20 volts!

My question: where to begin? Probably a internal alternator failure sensitive to impacts? Lose connection, lose ground in same place? What could be the cause of a voltage spike like this?

Car is in really good shape.

Thanks in advance for the hints.

Mauro Brisola
Multi Marcas
Curitiba, Brazil

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