1994 Chevy Astro Anti-lock light on

Anti-lock light is on when van engine running. The light went out once during a long drive, and the braking didn’t work properly; was pulling van to the right.

While parked, I checked for a diagnostic code, but no trouble codes showed up.

What is the most likely culprit?

The most likely culprit is a speed sensor, that is the most common cause of abs lights anyway. When your abs light is on, your abs system is disabled and does nothing, and should not cause any symptoms, like pulling. What about the brakes weren’t working properly?

The computer that you can access with a typical code reader (OBD I or II) does not store ABS codes. There will be a different procedure for the ABS module and different tools required. Get yourself to a brake shop.

Actually most OBDII (does not apply to the OP’s 1994) cars do have the ABS hooked up to the OBDII connector. However, a manufacturer specific code reader is required to be able to get the ABS and other codes. The generic readers only get the power train codes, and not all of those at that.

Good to know, thanks.

As long as the light is on, brakes work fine. So, your comment, “should not cause any symptoms” is consistent with what I experienced.
The light went out for a short time while I was driving. When I applied the brakes, I could feel the vibration when the anti-lock tried to work, but it interfered with the normal stopping range, so in retrospect, the fading to the right may have been a defensive reaction on my part to reduce the possibility of hitting the car in front of me.
When I stopped the van and started up again, the light came on and the brakes worked fine. Speed senor issue makes sense; looks like there is one on transmission housing for rear wheel drive.