what causes code p0620?

P0620 - Generator Control Circuit Malfunction ---- Possible causes - Battery charge, Faulty Voltage Regulator, Faulty Generator, Generator harness is open or shorted, Generator circuit, poor electrical connection, Engine Control Module (ECM) controlled generator, Faulty ECM ---- Read more: https://www.autocodes.com/p0620.html

The Engine Control Module (ECM) has fault detection circuitry which monitors the state of the generator turn on signal circuit. If the fault detection circuit senses a voltage other than what is expected, this P0620 code will set. The voltage regulator also contains fault detection circuitry. If the regulator detects a problem, the regulator will ground the generator turn on signal circuit, pulling the voltage low. This also causes the ECM to set the P0620 code.

thanks that's a lot I have 14 other codes +p0620

All those codes are a bummer but we can't help without knowing what they are.

Wow just saw this question and did not know when I answered the post with the 14 codes. Like I and F_O_R said you need to check this out first then to the Fuel Injection Control Module if everything else checks out good. You may just need a repair manual to get all the testing procedures and values to be able to test these. Last but not least expensive is the ECM itself. First thing I would do is check all the electrical connections and grounds to frame.

where is the fusable link that is in the alternator harnees on a 2008 ford super duty