ABS lite comes on at 15mph

I have a 93 GMC Suburban, I am posting here because there is no Suburban forum under GMC. I figure a Suburban is a Suburban etc...

The ABS light comes on at exactly 15 mph and goes out when I drop below 15mph. The diag code "Code 81: brake switch circuit shorted or open" displays when I short out the "A" and "H" terminals on the diag connector. I have a Chilton manual, but it's not much help. It's 4 wheel drive, one sensor on each front wheel and one on the back of the transmission. I'm not sure what they mean about the "brake switch circuit". Where can I find the circut diagram for the ABS that includes the brake switch circuit?

Thanks, Jim...

That is a very easy fix. Replace the brake light switch on the brake pedal. It is at the bottom of the brake pedal shaft. It is round and about 2 or 3 inches long with a plunger at on end and a wire connector at the other end. It just slides out and when you install the new 1 slide it all the way in untill the plunger is pushed in all the way in. When you press on the pedal the plunger should come out to complete the the wire connection and send the signal that the brakes are on.

Fireplug has the right idea here, but on the '93 suburban the brake switch is nothing like your typical switch, therefore there is no plunger.
When you reach in under the dash grab the pedal, and slide your hand up the pedal until you feel a plastic strap that wraps about 3/4 around the steel shaft of the brake pedal. reach up a little higher and you'll feel a small box about 1/2 thick, and 2inch front to back. Once you have this in hand pull the unit straight down. You will find at least one 4 wire plug, (2 plugs if you have cruise)
Buy a new switch, and installation is the reverse order.

FYI, the brake switch on these trucks use finger contacts that after time tend to wear down, and malfunction. It's probably a good idea to replace these switches about every 80k miles. Otherwise you run the risk of no brake lights, malfunctioning ABS, or Cruise.
for the cost of the part, it's worth the replacement to avoid the grief. :iceslolan

You guys just answered my question. I also have the same problem code 81. Will head down to the parts store tomorrow. I love this site.

OOPS forgot the switch was the half moon type

Thanks guys, I went and got the switch today. It was $13.02, I can't belive how long I went without anti-locks working or the cruise control. You guy saved me. Thanks again.

Happy to help