GPS Unit causing Check Engine Light on 2016 KW T-800

First of all, I do appreciate your time. The first answer made a few unfair assumptions and was a bit snarky, so that prompted my response. again, thanks.

So, here's a few more facts:

1) The unit is a 2015 T800.
2) The same GPS module has been on that truck for about 2 years and been otherwise flawless. To date, if we plug it back in it works fine for a while, then we start to get the data bus errors. They can be any kind of error - at first we were seeing DEF sensor error of some kind. It's been a while and I don't recall the specific error at the moment, but it was enough for Kenworth to replace the DEF sensor part - whatever it was. Honestly, I don't think it had even failed, I think the KW guys swapped it out because the error code told them to and it was still under warranty. Somewhere during the repair, the GPS unit was unplugged, so the road test after the repair went fine. We plugged the GPS unit in a few days later and no problems occurred for about a month. Then we started getting errors again. It was the DEF sensor one time, then it was a few other unrelated errors, like coolant level low (coolant was fine), and others. We unplugged the GPS unit, and magically, all the new errors stopped occurring. We plugged the same GPS unit into another truck - 2016 truck I believe - and it worked fine. No errors at all. We also put the same unit into a 2019, and it worked fine. Other GPS units are in various other units all T-800s from old (1997) to new (2020) and we have not seen any similar problems except on a 2016 that kept having speed sensor problems, but in hindsight I'm wondering if that was a malfunctioning GPS unit also causing the error. That particular truck is gone now, so we cannot test for that.
3) Sitting here at home, I'm not sure if the problem truck is running 250 or 500K, but I'll find out on Monday. I was not aware that they had changed the data bus speed and that is certainly something to look into, although the GPS unit worked great for almost two years in that, and continues to work fine in other trucks, so I'm a bit at a loss on that. It could be that it was capable of both speeds and somehow has lost it's ability for the slower speed.
4) Codes were all over the place. The speed sensor error was a "shorted speed sensor" one time. Another time an error told the ECM that the truck was doing (something like) 150 miles per hour and this caused the ECM to disable the throttle because that was obviously above the programmed maximum speed. Clearing the codes solved the problem temporally until it happened again. Kenworth replaced the Bendix Computer that time claiming that the Bendix computer was bad. Now, I'm doubting that also. I think the GPS unit was somehow screwing things up.
5) We've checked all the pin-out of the cables. They all line up the proper +12, -12, Data, etc. lines.

One thing that bothers me is that the units are packaged with OBD2 connectors and the GPS folks ship an adapter cable that goes from OBD2 to J1939. I didn't think a OBD2 device was compatible with the databus on the larger trucks, but all three GPS vendors I have spoken to assure me that they are and that they have "1000's" of units in place working fine.

It continues to be a mystery. My next step may be to put a logger on the truck and watch the databus constantly, recording every bit of data and see if I can see whats causing the error. I've done this before and the amount of data in an 8 hour shift is amazing. Thousands of pages.

Anyhow - that's my long-winded explanation. Thanks for your time.

 

Thanks. All trucks were factory delivered to us. I miss the days of non-electronic engines. I've got a Big-Cam 400 in an old yard-rat truck that is still purring like a kitten. Starts ever time. No regeneration. No DEF. It will probably be working well after I'm dead and gone. These new trucks with their numerous computers suck.

 

Yeah, we wired it according to the KW instructions. We did not use the diagnostic connector.
I was not aware of the baud rate change, so that's something that we will be looking at, however all of the units have been working fine for just under two years or so, so I'm assuming they are somehow auto-adjusting to whatever baud rate they are connecting to. As I wrote before, I'm wondering if the comm chip in the GPS unit is failing now and is having periodic problems with comms and somehow screwing up the databus. The truck that has the most problem is a 2015, and the rest of the fleet is mostly newer and doesn't seem to be having any problems. A 2016 truck that we used to have was also experiencing problems, and I'm wondering now if that was GPS unit induced as well.

 

I'm not sure that we've tried the know good-unit thing yet. I'll add that to my list of stuff to do this week. Honestly, the customer service from Azuga was so piss-poor that we are trying out another vendor (GeoTab) and as soon as we plugged their unit into the 2015, the 2015 started throwing errors too. GeoTabs answer was "we have these in a ton of Kenworths, they all work fine." So, the question now is "what year Kenworth?" I guess.

I'm also curious about the self-update issue. That's the only way i can explain why they began to fail after working for so long. My only other theory is that the units are just degrading and the comm chips are not working like they used to....but that's a bit of a stretch, they are not that old yet.

I'll fill you in more as I learn more. Thanks for your interest.