ABS Sensor is On..

[gbear711]

If different wheel size did not cause a trouble code to be generated why would they have it in the DTC?
it may be one of those oddball things that happen occasionally and it hasnt happened to you. I have been filling my gas tank while my engine is running and never had the check engine light activate until last week, I may fill it for a year and not have it happen again. I have an 89 c1500 350 with RWAL and when i drive it the abs light never comes on, when my son drives it it always does, the famous 8 flashs (dump valve if i remember right).
I (and others) think its due to his heavy foot causing the vacuum to drop. With 250,000 miles I'm not worried about it, it still stops when i want it to.

[gbear711]

I wonder if Sykopenguin has checked his brake fluid? I think I would do that before looking at the tires.

[Fireplug]

The ABS system is set up to use 1 or 2 matched set tire size. Going over or under that could but not always set a ABS code. That is right out of the GM ABS Training manual. In 1994-1996 Blazers we had a bunch where the owners would lower the truck and put on very big rims and it was setting wheel speed sensor codes because the speedo and wheel speeds did not match or be with in 3-5% of each other. A prom updat to the pcm fixed most of these problems. I could go into a lot more of why and how this works but I think you get the idea.

[sykopenguin]

I Pulled codes 86 and 13 from the ABS system....13 is under RWAL and 86 is under 4WAL
13 = Faulty ECU.
86 = Check the light and wiring for a short circuit.