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Mercedes Voltage Question

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3 years 5 months ago #44755 by Tyler4029
Mercedes Voltage Question was created by Tyler4029
Diag question

I work for an indie shop and we mostly send our customers to a good diag shop for check engine light stuff.

The other day I had some extra time and decided to play around with diag before sending it off.

It was an 08 Mercedes Sedan (something 350)

I cant think of the code off hand, it was possibly p0012. It was a VVT code. Bank 1. I know that much.

Long story not so long, I measured voltage at the plug of the VVT solenoids for both banks. Unplugged. 12v on one terminal, 3v on the other.

Voltmeter grounded to engine block.

Why the 3v?

Should it not be 0?

The car is in better hands now so I cant go back to it. I’ll know the answer once the diag place sends it back but was just curious in the meantime.

Thanks

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3 years 5 months ago #44756 by Matt T
Replied by Matt T on topic Mercedes Voltage Question
Sounds like bias voltage on a ground side switched circuit. ECM uses it to monitor for circuit faults.

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