I understand that the code diagnoses this...

P1820 Internal Mode Switch Circuit A Low

I think this circut is in the transmission and I need to know if this is correct and how to test it.

1997 Tahoe 5.7l, 4L60, 4 wheel drive, stock everything.
Thanks, Kyle

 

Welcome to the forum...
boy that is a tough code to find
I found this on another forum...
http://www.s10forum.com/forum/f105/w...1870-p-301660/

 

I read that one last night while googling the code. I am wondering if the code could be because the owner had low transmission fluid level. Hopefully someone can at least tell me what circuit A is, is it a fluid circuit or an electrical circuit.
Kyle

 

The only code I can find in my repair manual is a P1825 which sounds similar to the 1820

attached PDF

 

Looks like your manual is for 2007 Chevys. This is a 1997 with a 4L60 transmission. I don't know which tranny you have but I cant imagine they are the same, so the codes may be different. I see what you mean about the similarity between the description of the codes. I am not sure they are related though. Thanks.....
Kyle

 

I have the 4L60E but its more electronically controlled then the 97, however the document might help give you some general direction as the codes for the most part do not change...

 

I drove the truck again today and have not had the CEL return. I will recheck the codes on Monday to see if it has returned without lighting the CEL. Thanks for the help.
Kyle