On my 91 camaro rs the check engine light doesnt come on at all, not even on ON position. and also i maybe wrong on this but is pin d on the aldl connection the one for codes or pin b and a? because if it is pin d im missing it. Thanks Martin

 

It is pin A and B. Pin B is the power and pin A is the data

 

pin a is ground, pin b is mode select, pin e is 8192 data, and pin M is 160 data. But for testing you just jump across a and b if you have a 90-92 and 85-89 you jump with a 10k resistor across A and B.

 

i been trying to solve the problem but cant figure it out. sometimes the check engine light comes on with the key position on (engine not running) but most of the times it doesnt come on. and the other day i tryed to pull the codes and the onling thing that would come on is the brake light and thats it. do i have a loose connection or something?
Martin