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Discussion Starter #1 (Edited)
Hey forum new here.

Needing some assistance on a P0620 code(Generator control circuit)

I have an 05 c230k that has aprox 132k miles.

I checked the voltage using the onboard odometer display and it read between 14.2v to 14.5v when the car was turned on.
Seems like its getting plenty of voltage though I do notice a very slight hesistation from time to time when turning the key/ignition. After the car is on and running, I have no issues or dimmed lighting.

Would this code point a faulty voltage regulator? Or altternator going out soon? Any faulty relays that could trigger this? I do also notice a slight corrosion on the battery terminals.

Any suggestions would be appreciated.


 

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2003 C320 coupe, 2000 ML320
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I checked the voltage using the onboard odometer display and it read between 14.2v to 14.5v when the car was turned on.
Seems like its getting plenty of voltage though I do notice a very slight hesistation from time to time when turning the key/ignition. After the car is on and running, I have no issues or dimmed lighting.

Would this code point a faulty voltage regulator? Or altternator going out soon? Any faulty relays that could trigger this? I do also notice a slight corrosion on the battery terminals.

Any suggestions would be appreciated.

Sent from my LM-X210(G) using Tapatalk
At some point (up to 15 minutes), voltage should be dropping off into the high 13s.. not dropping down indicates the battery isn't taking a charge.. Could be the terminals or a battery on it's way out..
 

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Discussion Starter #3
At some point (up to 15 minutes), voltage should be dropping off into the high 13s.. not dropping down indicates the battery isn't taking a charge.. Could be the terminals or a battery on it's way out..
This was today idling in park.
When i turned to the first position, it read 12.2v... Could it just be a low battery?


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12.2v is a tad low.. 13.7v looks ok... How old is the battery? Did you ever clean up terminals?.. Does the fault code come right back, if you clear it?
 

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Discussion Starter #5
12.2v is a tad low.. 13.7v looks ok... How old is the battery? Did you ever clean up terminals?.. Does the fault code come right back, if you clear it?
Cleaned the terminals yesterday with battery terminal cleaner and a wire brush. The left negative cable looked a bit worn on the clamping end with a very worn nut that tightens the metal around the left battery post. The battery is a Varta brand but not sure when ot was last changed.( purchased the car used)
 

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Discussion Starter #6
Cleaned the terminals yesterday with battery terminal cleaner and a wire brush. The left negative cable looked a bit worn on the clamping end with a very worn nut that tightens the metal around the left battery post. The battery is a Varta brand but not sure when ot was last changed.( purchased the car used)
Cleared the code and came back.

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With the car running, alt. putting out 13.7v (run car until it does).. Clear fault.. Does it come right back after you clear it..(with the car running).. The 13.7v looks good (alt putting out and battery taking the charge) and shouldn't be throwing a code..
 

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What happens when you rev the engine? Voltage will drop due to power pulled needed by the fuel pump and coils. If it drop much lower than 13.5v, I'd think it's an alternator issue, but then again, it could also be a bad battery cell that will act like a huge resistor and drop voltage. To check for that, disconnect the negative battery lead with the engine running and observe the voltage.
 

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Discussion Starter #9
What happens when you rev the engine? Voltage will drop due to power pulled needed by the fuel pump and coils. If it drop much lower than 13.5v, I'd think it's an alternator issue, but then again, it could also be a bad battery cell that will act like a huge resistor and drop voltage. To check for that, disconnect the negative battery lead with the engine running and observe the voltage.
Just messaged the guy who sold me the car. Apparently he states the alternator was "rebuilt" so that is why the light is coming on...

Possibly an aftermarket parts used?
 

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As long as the bearings are good, generally the alternator itself does not go bad, although there are some diodes on it that can fail. What causes problems is the voltage regulator. It's on the back of the alternator and can be replaced as a separate part.

But again, did follow my advice above? What were the results?
 

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just a thought- my 2002 C320 had an alternator code coming back so i changed the alternator...when i replaced it i found that the small connector plug (not the 12v thick wire) was broken on the alternator so the computer was not seeing the alternator charging i suppose...
 

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Discussion Starter #12
Just an update... battery is good and was confirmed. What is strange is that there are days were it does not drain and if it does, it is very minimal(12.4-12.1). The battery starts right up with no issues, then other days it has a slight hesistation then picks up upon cranking.

Odd thing is that when it is in the first position(engine off) Battery reads 12.2-12.7v when turned on under load, voltage reads 13.6-13.7. Car runs fine.

What I am noticing is when I switch out the bulbs that supposedly need changing(all are new) one either gets semi burnt out, and when replacing, I turn the car on and the voltage immediately drops to 10v to 11.2.

The car no longer starts and needs to be jumped to start again.

This happened a second time today as I was changing one of the supposed bulbs that was popping up on the message screen.

So now im thinking is this a combination of an alternator issue/voltage regulator? Or could there be a circuit/short problem going on in the wiring going to the bulbs.

No other codes are present except p0620.


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Just messaged the guy who sold me the car. Apparently he states the alternator was "rebuilt" so that is why the light is coming on...
That makes no sense. It's like saying "The reason you're getting bad mileage is because I installed new spark plugs". 😆

If it was a rebuilt alternator, it shouldn't be throwing codes.
 

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Discussion Starter #14
That makes no sense. It's like saying "The reason you're getting bad mileage is because I installed new spark plugs".

If it was a rebuilt alternator, it shouldn't be throwing codes.
Exactly... Im sure he was lying on his end and just did not want to put the time and money on a quality alternator/voltage regulator..not surprising.

Just ordered an alternator today and will install soon.

Hope this takes care of everything

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