03 Chevy Astro no com

Hi guys, I've got a weird one.
2003 Chevy Astro van. 4.3l RWD, California emissions.

It's a used car that just had a transmission installed. It's unknown if this problem existed before the transmission job.

When connected at Massachusetts State inspection, there is no communication.

There is no issue communicating with this van in enhanced or generic mode with my Verus and the shops Modis.
Even the hand held code reader works fine.
I loaded the power and grounds at the DLC, the pins seem fine.
It's been to two stations and both have no communication. One tried disconnecting the alternator with no effect.
No codes, no drivability issues.
Just won't get a sticker.
Any advice will be greatly appreciated!

Whoa, my Personal Feed on iATN is blowing up, found your thread.

Very weird. :ohmy: There's just not that much to this DLC... Pin 16, 4, 5 and 2 for the Class 2 network. They all have to be working, otherwise your scanners wouldn't talk to it. :blink:

What is the inspection machine doing differently... I'm assuming both shops this van went to use the same standardized testing machine?

What kind of weirdness did you see on pin 2 when backprobed? Any chance you could post a capture?

Tyler wrote: Whoa, my Personal Feed on iATN is blowing up, found your thread.

Very weird. :ohmy: There's just not that much to this DLC... Pin 16, 4, 5 and 2 for the Class 2 network. They all have to be working, otherwise your scanners wouldn't talk to it. :blink:

What is the inspection machine doing differently... I'm assuming both shops this van went to use the same standardized testing machine?

What kind of weirdness did you see on pin 2 when backprobed? Any chance you could post a capture?

The DLC is about as basic as they come. Everyone I mention it to thinks that the inspection machine must get it's power from a different pin :pinch:
Thank goodness we know better than that.
I loaded the power and two ground with a headlamp bulb (although I arrived at the same logical conclusion as Tyler that they must be fine since my tools play fine with it), and it was super bright.

I did a half assed job scoping the data line at work, so I took the van home and did it again in the driveway just now.
KOEO, KOER (no loads & all accessory loads) 10v scale, 50ms sweep ( :lol: ) all I saw was tightly packed 0v-7v square waves with longer periods of low voltage in between signals. So, nothing remarkable, no real noise or hash. I could be wrong, but it looks about what I expected to see
I'm working on uploading a capture. I zoomed in too much (because you can only zoom out on captured waveforms with the Verus) and ended up with a short buffer, so the best one I saved isn't great.



I wiggled and tugged the PCM connectors, and tapped the PCM with a screw driver. I tugged the DLC harness and looked for any alarm system or aftermarket garbage.

The only real work I can suggest is changing the DLC. The pin fitment seems nice, but it's the only common denominator I can see.
I just can't recreate the fault.

Does the inspection machine automatically identify the vehicle, or does it used a scanned VIN to determine year, make, and model? It is possible that if you just scan the VIN code in that it is identifying the vehicle as an 03, but the engine computer could possibly be out of a different vehicle causing this issue. What does your Verus automatically ID the vehicle as being? These vehicles are known for computer problems, and a past PCM replacement is definitely not out of the question. If this happened and the programming was not performed properly it may be your issue, but I am unsure.

I see you fixed it . Think you can upload an after capture of the data communication?

SniperDan wrote: I see you fixed it . Think you can upload an after capture of the data communication?

Yup, got it sorted out! Thanks for your help, that's an interesting idea about conflicting configurations. Honestly, I never thought of that!

I ended up changing the DLC connector with one from the junkyard. It was about the only conclusion I could come to, and when the problem was brought to my attention by the mechanic working on it at the time, that was my first response to him. So I went with it. Maybe it's parts changing, but it was the most logical failure I could think of.
I checked the pin drag on the new (used) connector and it felt the same. I guess I need to develop a better method to gauge pin fitment
(Wasn't there a thread about making a tool to check DLC pin drag? Maybe on the last forum?)
Here's the after captures. They look the same to me, but I expected that.
The first one is set up like the original capture for comparison, the second one is a little shorter time and easier to see.
I have the .VSM files if anyone want's them to view in Shop Stream.






Thanks again for the help and ideas

Sweet. This customer has NO idea how much money you saved them. This could have easily ended up in the hands of a hack, and gotten a shopping cart full of modules and harnesses thrown at it. :lol:

Just had a thought... I'm sure the DLC pins were worn/pin fretted somehow, otherwise replacing the DLC wouldn't have fixed it. BUT, what if the male pins on the inspection machines are worn, too? They probably get cycled at least a few times a day, for years on end. Worn male pins + marginal DLC = no com?

Also, does this DLC mount vertically? As in, the female pins point at the floorboard? 'Cause I can see people ripping scanner connectors out at an angle, and spreading the DLC pins in the process.

I was thinking the same as Tyler.
I'm sure the inspection machines see a LOT more cars than my Verus does, so I'm sure the wear on those pins coupled with a DLC which probably has been around the block a time or two were the perfect recipe for this problem. I'm just glad it's out of my hair (so is the boss!)

Seriously, EVERYTHING checked out fine, what else was there to do?