Reading ALDL Connector Codes

[Stepperado]

I found the section of my Emissions & Drivability Manual that speaks to the ALDL connector, how to enter the diagnostic mode, and see codes. It also has a page the describes what each code is for.

What I don't see is any guidance on how to interpret the "check engine soon light show" that takes place in diagnostic mode. It just says you will see flashes, pauses, etc. It did tell you what a "code 12" looks like, but what about all the others.

Any guidance would be appreciated. I occasionally have a check engine light that goes on, but it goes away after a restart. I'd like to read the code that is stored.

Thanks,
Randy

 

[1987 GMC Jimmy]

Well, assuming you know to stick a paper clip between A and B (top right two pins) and turn the key on, it'll flash that Code 12 three times as you see it will in your manual. Then it'll sequence your three stored trouble codes. Say you have an EGR valve problem, Code 32. It'll flash three times, pause for just a second, and flash two more times. It'll pause a little longer and proceed with the next code. So basically just count the flashes and cite your manual.

 

[chengny]

The pages below provide a little more detail as to how the flashes are grouped and the length of the pauses between individual flashes and the groups.

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The strange thing is, the way I read it - it appears that in 1984, there were no GM light truck applications (outside of CA) that even came equipped with an ECM (AKA a computer command control system). maybe your truck is Californian:

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The pages below are from the 1987 emissions & drivability manual - that was the first year I was able to find that GM generated a dedicated D & E manual. But when compared to the 1984 California sections, it is identical:

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[Stepperado]

Thanks guys, that's exactly the kind of feedback I was looking for.

Again, gotta love this site. Fun to watch and a great resource when you need it.