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Does this look normal?

doughboy18718

doughboy18718

Diesel Retard!
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The Burg, VA
I am slowly but surely getting back into working on the diesel, and am trying to get any codes i can from it. I recently purchased a code reader that does both OBD-I and OBD-II. I cannot seem to get the scanner to read my Yukon though. I wanted to ask if my connector looks like everyone else's?
 

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You can look up in the stickies for the paper clip method to read the codes on pre 95 trucks. Does your reader have a switch that you have to change from obd1 or 2?
 
can you get the codes by jumpering pins A&B of the OBD1 port? And count SES light flashes? Does your SES light come on when the IGN is ON, Engine OFF?

That looks normal, do you have to set scanner in OBD1 mode?

You could have an open circuit to the PCM
 
Rodd said:
You can look up in the stickies for the paper clip method to read the codes on pre 95 trucks. Does your reader have a switch that you have to change from obd1 or 2?
Click to expand...

Yes, the reader can be, and was set to the OBD-I setting for GM's, but no luck
 
buddy said:
can you get the codes by jumpering pins A&B of the OBD1 port? And count SES light flashes? Does your SES light come on when the IGN is ON, Engine OFF?

That looks normal, do you have to set scanner in OBD1 mode?

You could have an open circuit to the PCM
Click to expand...

I haven't tried jumpering it yet, but i don't have an SES light (i'm sure i do, but it is either burnt out, or doesn't like me and won't come out to play when i want it to)
 
I guess i should mention that the fuse that fuse that is supposed to be in the center of the fuse box wasn't there until tonight, and looks like it was melted so it may not work now
 
The truck runs fine though? You should have an SES light, and it sounds like you have an open circuit to the PCM. With IGN ON Engine OFF do you see the Serive Throttle Soon light?

For the SES light, is your guages fuse blown? You can try replacing bulb, or you can see if the PCM is not operating the light correctly. If you pull out glove box liner you can pull PCM out from the corner. Its not bolted down just clipped in on the front, remove. You can pull the whole thing out or just pull out the Blue 32 pin connector. With IGN ON Engine OFF, if you ground pin D5 (brown/white wire) it should light up the SES light. If the SES lights up then the PCM is not doing what its supposed to and will have to check the PCM grounds, which I'll look up if you get there. If light still doesnt work then bulb is blown. Turn IGN OFF and hook connector back up.

That might prevent the serial data from working. Using test light or multimeter check to make sure that pin A of the OBD1 port is grounded (probe to it with test light and other end connected to 12V source, test light should light up).

If you want more info on testing the serial data circuits to the PCM let me know I can post it.
 
The SES light paperclip works off of a data request signal that happens when you ground pin B by jumpering it to pin A (which is an engine ground).

The Scanner uses a serial data line that goes to pin M which may be broken.

So SES and scanner work off two different signals. Can troubleshoot the lines if you want that info.
 
Got it. I would not mind getting that info. Since it looks like it may be a common occurence and DB may need it too.

Thanks!!!
 
I'm thinking DB's problem is the SES light burnt out or an open SES light circuit otherwise and that is inhibiting the PCM from sending serial data. The SES light grounds in the PCM, and that is how it is controlled, when PCM want to ground the circuit, and if the PCM doesnt detect the voltage coming in then I think it inhibits serial data.

However To check the serial data circuit you could leave engine IGN OFF, pull off the Pink 24 pin PCM harness and find contact C14 (orange/black wire), C is the row against the harness clip. Go jumper OBD1 pin M (bottom right) to pin A (top right) which will ground it. Clip a test light to a 12V source and probe PCM harness (not the PCM) at contact C14. The test light should light up, if not that line from the PCM to the OBD connector is broke. If the test light is on, then will have to troubleshoot further.
 
buddy said:
The truck runs fine though? You should have an SES light, and it sounds like you have an open circuit to the PCM. With IGN ON Engine OFF do you see the Serive Throttle Soon light?

For the SES light, is your guages fuse blown? You can try replacing bulb, or you can see if the PCM is not operating the light correctly. If you pull out glove box liner you can pull PCM out from the corner. Its not bolted down just clipped in on the front, remove. You can pull the whole thing out or just pull out the Blue 32 pin connector. With IGN ON Engine OFF, if you ground pin D5 (brown/white wire) it should light up the SES light. If the SES lights up then the PCM is not doing what its supposed to and will have to check the PCM grounds, which I'll look up if you get there. If light still doesnt work then bulb is blown. Turn IGN OFF and hook connector back up.

That might prevent the serial data from working. Using test light or multimeter check to make sure that pin A of the OBD1 port is grounded (probe to it with test light and other end connected to 12V source, test light should light up).

If you want more info on testing the serial data circuits to the PCM let me know I can post it.
Click to expand...

Yes, the Service Throttle Soon light does come on, and no the truck doesn't run right now. I will try this tonight after i crawl out from under another bowtie. Hopefully i can get narrow this down soon, or i'm going to offer this truck up to the highest bidder!
 
My goodness, the truck doesnt run is a very important piece of info. Any more info you can provide would be good, fill out the checklist. Like, does it crank, does the Glow Plug light come on and for how long, is there fuel to the injectors.

Sounds like you have some sort of PCM issue, whether it be a broken wire or a fried PCM there are checks to do to figure it out. So let us know everything you can in the Diagnostic Checklist.

First thing is to check that the ECM-IGN fuse is actually good.
 
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