You can do it yourself without a scanner/code reader. Just pulling codes that is. Look at you tube but all you need is a paper clip and pen/paper. Look at your connector, under the dash. Put the clip in the top two spots on the top row right. A and B circuit. KOEO=Key On Engine Off. Watch Service Engine Soon light. Should start to get flashes and should start with code 12. One flash and then 2 flashes after. It does that three times and then codes start. Count the number of flashes and each code will do it 3 times. Then code 12 to finish it out and tell you it is done.
I just found the ALDL physical layout/electrical pinout info in the '94 FSM Electrical & Diagnostic manual.
This illustrates what movievet was accurately describing:
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Searching Tip:
I opened up my local copy of this manual, did the old school 'Ctrl F' (Find function)
typed in 'ALDL', and got *nothing*. Looks like this acronym was never used by
the Tech Writers in this particular manual? Instead, they used DLC, for Diagnostic
Link Connector.
But I didn't know the DLC acronym. But what I did do was read around a little bit,
and electrical circuit "451" was identified as the one used for 'diagnostic test'. So
I searched the entire manual for '451', and in seconds it found this number in 35 different
locations. And on the 2nd instance I ended up with this.
I share all this with you coming from the perspective of owning my own full set of paper
manuals for my '99 chore truck. And I enjoy reading from them. But when I need to find
something quickly, these .pdf files on a fast laptop is such an unfair advantage.
If you are reading this, and as yet haven't downloaded the electronic versions of the FSMs
that cover your machine, please do so at your earliest convenience. It's a game changer.
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