My wife started up the car to go shopping and the car started singing and gave her the battery light on the dash. I hooked up my scanner and pulled a P0621 code. This seems like a " it could be anything code" related to the ECM. I recently changed the battery ( about a month ago) the original battery finally started to die. Other than that no work on the electrical system.

I will start checking battery voltage, the connections at the alternator and connections at the ECM modules.

Anyone have any other suggestions?

 

Looks like battery or alternator.

But as reported here: EFI Live autocal versus the code reader. P0621 P0128 - Chevy and GMC Duramax Diesel Forum some readers incorrectly report P0621 when the code is actually P0128, which points to the thermostat.

 

Sounds more like the ECM reading the alternator demands, per this link



P0621 Chevrolet Generator Lamp L Control Circuit Malfunction OBDII Engine Light Trouble Code | Engine-Codes.com

 

"car started singing and gave her the battery light on the dash."

That didn't say "the alternator is bad" to you? By that, I mean any part of the alternator that spins.

 

Sorry, damn auto correct... I meant "Dinging" as in the the warning chime / bell went off in the car.

I did change the thermostat, coolant and hoses about 6 months ago after getting a code regarding temp.

oldblue Alternator is on the list and is the first thing I thought it could be before hooking up the scanner. I'm checking that. It's just such a vague code that I can end up on a wild goose chase.

Wanted to check in to see if anyone has run in to it before.

 

I thought it sang!! " See the USA in your Chevrolet!"




But maybe it didn't know the words!!!


I'd get the charging system tested, it does sound like the alt is headed south!!

 

Was it an OEM thermostat? You may want to check it with a different reader.

 

What is vague about it?
P0621 Chevrolet Generator Lamp L Control Circuit Malfunction OBDII Engine Light Trouble Code | Engine-Codes.com

Seems darn clear to me. The circuit inside the alternator that sends an receives the "turn on" signal is broken.
I guess it could be the control wire or contacts are bad, or the ECU is bad (remote possibility).

 

I have noticed that the plug for the control wires is a really stressed connection.

 

Donbrew Got it. Thanks.

LOL oldblue.

RJ - No. I think I got it at Autozone. Why? Should I replace it with an OEM?