Codes

[Seahorse51]

I understand how to jump the a & b terminals to atemp to read codes on the ltpws, however when I do this I get this: Service engine light gives me the 1 & 2 then the service ltpws light gives me a 12 and then gives me a 54 three times. According to Chilton, 54 is EGR #2 problem or fuel pump circuit (low voltage) or shorted mixture control solenoid circuit feedbac carburetor system. The only warning I get on the panel during driving is the ltpws.

What gives?

 

[jmccloud]

error codes

There are several groups of error codes. 12 is the beginning code to indicate that you're reading. The if nothing follows, it's all clear.
Different years of C5's have different codes and code groups. I don't know them for a '91 but it sounds like you're in the all clear for the ecm (12 only) but have a code 54 in your ltpws. The Chiltons 54 is for the ecm, not for the ltpws (where your problem is). A Helms (GM) manual will spell out the detail code groups and codes for each.
Hope this helps