Electrical Problem ?
 

Hi All,
I'm new to the site and looking for help. OK, I don't have a Suburban but it's cousin the Yukon XL.
I think they are pretty much alike mechanically.
I've had a series of problems, mostly based mostly on electrical problems which were solved but now I'm stumpt.
I had a small evap leak code which I cleared and it took two weeks for it to come back.
I replaced the gas cap with what I thought was a good used one and cleared the code again.
The code came back a few weeks later.
I cleaned some debris from the o ring , put some silicone grease on the o ring, put ti back in and cleared the code.
I thought I was fine.
Now, several months later I took the truck for a state inspection.
No codes in memory and no service engine light on.
The truck failed and the mechanic showed me a check engine light and a code for evap leak.
I've changed both purge valves, put on a brand new gas cap and cleared the codes.
I've now done 8 drive cycles and can't get the OBD2 computer to show all sensors working.
Presently the HTR and EVAP sensors are not reporting.

One more piece of info ..... Before going for inspection ...... We had parked the truck at the airport for a week. While we were driving home and after the engine had reached normal opperating
temperature, the gauge dipped by about 25 degrees and then after about 5 minutes it came back to normal. This happened twice.

Interesting that in between the first two drive cycles I went back to the dealer and when he put his instrument on the car, it made clock in the radio go off time, as if the battery had been disconnected.
Since that time, I have not returned to the station but used my own OBD2 reader.
It does not cause the clock to go off time but still shows the HTR and EVAP monitors not reporting.
I now have almost 400 miles on the truck and still no joy
Any ideas ..... the battery is 4 years old but starts the truck fine every time and voltage is good.

Post the code.

That's the thing ..... THERE IS NO CODE IN MEMORY.
I've completed multiple driven sequences as listed with GM and no codes are present.
Another user who had a similar problem posted on You Tube to disconnect the battery and wait half an hour before reconnecting it.
He said that clearing codes in his case would not permit drive cycle to complete but he had a partial completion after doing the battery disconnect.

If I had a code, it would be GREAT .... I'd have something to go on.

Code - Problem
 

There were no stored normal codes but I was able to find U1303 .... communications code
1 - low
2 - high
3 - high

Batteries are exspensive, but that can take on thing out of your troubleshooting equation. Even if it is a 6 year battery, those don't make that especially with any extreme hot or cold seasons, just a thought.

I thought about the battery but have monitored it's voltage and does not seem to be an obvious problem. I could try to temporarily swap it out with one of my other vehicles. I'm thinking more along the line of a ground problem some place but don't know where to start. I'm in the process of getting schematics and pictorials for the wiring of the vehicle. I have a Haynes manual but it's not the greatest.