I've been trying to diagnose the problem with my '91 Firebird. It runs crappy but doesn't throw a code. I discovered the the SES light doesn't work. I checked the bulb, and it's good. The SES light never comes on, even with the key on, engine off. It doesn't blink to pull codes with a paper clip in the ALDL either. What would cause it to malfunction like that? Is it a common problem for later 3rd gens? Is there an easy fix(I hope)? I searched, but couldn't find anything. Thanks for your help.

-Erik

 

The ECM wiring, dash wiring, or ECM lamp driver may be faulty. Obviously, the ECM is operating, or the engien wouldn't run.

You may be able to diagnose error through the ALDL port. You can try to connect a test lamp to a +12VDC source and terminal D at the ALDL. If the test lamp operates as the SES should, the dash wiring is suspect. If the test lamp doesn't operate, the ECM wiring should be checked.

 

I had the same exact problem. Was going to fix it but ended up going from TBI to carb, so i just said screw it. Good Luck

 

I checked it out today, as Vader said to. It appears that position D on my ALDL plug is empty. There is no electrical pin in that terminal. What's the deal with that?

 

Mayor Dave probably banned it from your ALDL. Figures.

Lacking a socket in the D position, go back to the ECM connectors and probe the brown/white wire at pin A5. that should be connected to the MIL lamp.