I suspect a short-to-voltage issue on can bus. Scanner not communicating with multiple modules. Car running fine.

2019 GLS 450
Original Starter Battery - Napa indicates battery is good. Fully charged on NoCo 5amp maintainer. 12.4-12.6 V
Unknown condition of AUX battery (but no warning lights)
No parasite drains detected.

Car runs fine. No fault codes (but that could be lack of module communication). No warning lights. I do think the battery doesn't hold charge well (maybe loses 0.1V/night, but no parasite drain detected).

I'm using a Youcanic UCAN II C Pro OBD2 Scanner. I am not detecting all the known modules for this car. Example: "no response" on ISM, Transfer Case, Chassis Gateway, etc. Scans performed with key in position 1 (accessory), position 2 (ignition, but engine off), and with engine running.

I suspect some sort of can bus communication issue.

OBD2 check. Battery not disconnected. Door is open (but sounds like system is cycling on and off)

System OFF:
Resistance across Pins 6 and 14 - 60 ohms. [good]
Continuity between Pin 4/5 (ground) and Pin 6 - 0L open line [good, no short-to-ground]
Continuity between Pin 4/5 (ground) and Pin 14 - 0L open line [good, no short-to-ground]
Here is my problem (I think)
System Off: Voltage across Pins 4/5 and 6 (~11.5)
System Off: Voltage across Pins 4/5 and 14 (same voltage as on Pin 6)
System Off: Continuity check Pins 6 to 16 (power) - 0L open line [good, but I understanding a short-to-voltage may not run back to Pin 16]
System Off: Continuity check Pins 14 to 16 (power) - 0L open line [good, but I understanding a short-to-voltage may not run back to Pin 16]

System ON (engine not started)
Voltage across Pins 4/5 and 6 (2.5V-2.6V) [good, turned on but maybe in standby mode - not actively transmitting data] - not using an oscilloscope
Voltage across Pins 4/5 and 14 (2.4V-2.3V) [good, turned on but maybe in standby mode - not actively transmitting date] - not using an oscilloscope
System ON (engine running)
Voltage across Pins 4/5 and 6 (2.6V - can HI) [good, transmitting data] - not using an oscilloscope
Voltage across Pins 4/5 and 14 (2.4V - can LO) [good, transmitting data] - not using an oscilloscope

Questions:

1) I suspect a short-to-voltage on the Can bus Hi and Low. Is this likely correct?

2) If there is a short-to-voltage and I only get a "no response" on the scanner for modules that I know should be on the car, do I need to worry about this if the car is running fine and the system modules are working? Basically, I know tracking down a short-to-voltage can be tedious.

3) If I do need to track this short-to-voltage down, does anyone have the can bus locations for a 2019 GLS 450? I understand one or two may be behind the front passenger kick panel. I figured I'd start with disconnecting the modules at the can bus and rescan to see if I can find the faulty module pulling down all these other modules.

4) Do I just need to sit down and shut up and enjoy a good driving car?

 

try another scanner?

 

Launch Creader Elite V2.0 provided the same "no responses" for the same modules. Thanks for the clarity.

 

Tried to find can buses today. Didn't see them under the passenger kick panel; although I found the front SAM. Tried to simply remove all the fuses I could get my hands on to see if I could stop the 11-12 v running through Can Hi and Lo when the bus is off. I pulled the fuses in the engine bay (passenger side); passenger side dash; under 2nd row of seats but nothing impacted the 12v on the Can H and L when bus is off). [Note: I did not remove the grande 40 amp fuses or relays] I also did a 20 min negative cable starter battery disconnect.

Well, now I have legit error codes coming up "short to positive" And the following no longer work, although they worked fine this morning.

Left license plate light (B17F715 short to positive)
Left rear blinker (B164A49 internal electrical fault; B164215 short to positive)
Left brake light (B16AF15 short to positive)
Center brake light (B16B715 short to positive)
Right tail lamp (B285415 short to positive or open circuit)

2nd row courtesy lamps (under front seats). No code, but just stopped working.

So, I guess my theory on the OBD2 indicating a short to positive was correct.


Any idea if this is affirmatively the Rear SAM? Is the Rear SAM integrated into the 2nd row fuse box?
Could the original starter and aux battery be doing this even if I have a tender on the battery during testing? [battery "tested" good at NAPA]

I'm probably done messing with it and will take it to the dealer, but wanted to do a quick check to see if this has happened to anyone else.

Grazie

 

Your car is not equipped with any of those modules: ISM, Transfer Case, Chassis Gateway.

About the phrase "short circuit to positive", the translation is — 'no ground.' Usually a connector that you forgot to put back.

 

@trigital Well, sometimes the simplest of solutions! Yes, when I replaced to cover off the front SAM yesterday, one of the connector's latches wiggled loose. I just had to snap it in place this morning. Unbelievable. Everything came back. I guess the diagnosis of simply retracing your steps is tried and true. I can get wrapped into the details and miss the obvious. So, thank you. As for "missing" modules, I'll let that rest. I just assumed that ISM, Transfer Case and Chassis Gateway modules were standard. If it isn't broken, don't try to fix it.

Thank you again.

 

Great, happy for you!

Generic testers....use generic algorithms. The main problem of modern cars is trusting a generic tester.