ABS light stays on after disengaging the CDL, some times.

[Rusty Marlin]

7 pin mod. With CDL switch in the dash.
We have a lot of sand roads around and here and its common for me to go from pavement to sand and activate the CDL at speed (20-50 mph) but under no throttle load, just let it coast until the CDL engages.
ABS light comes, CDL light comes on, CDL engages. Apply power and away we go.
Get to the end of the sand and disengage the CDL, again under zero throttle load and if I'm clipping right along (20-50) the ABS light goes out and the CDL light goes out and the CDL disengages.
But if I forget and turn the CDL off when stopped or as I'm rolling slowly up to the intersection, the ABS light stays on, while the CDL does its thing and the light goes out.

Is there a speed at which the ABS stays deactivated when turning off the CDL? It definitely seems speed related.
This is probably in a manual somewhere, isn't it? But My google foo is failing me.

 

[NeverFinis]

My guess is the ABS ECU must see the wheel sensors working operating before enabling.

Although, I think I can go into and out of 4WD Low while parked, and the ABS light goes out after.

Most info is in the diagnostic section of the FSM, about DI-178 in my FSM. Some is in the Brake section, about BR-50, and some is in the EWD.

The FSM does mention 20 km/h as a speed point for testing....

 

[ppc]

7 pin mod. With CDL switch in the dash.
We have a lot of sand roads around and here and its common for me to go from pavement to sand and activate the CDL at speed (20-50 mph) but under no throttle load, just let it coast until the CDL engages.
ABS light comes, CDL light comes on, CDL engages. Apply power and away we go.
Get to the end of the sand and disengage the CDL, again under zero throttle load and if I'm clipping right along (20-50) the ABS light goes out and the CDL light goes out and the CDL disengages.
But if I forget and turn the CDL off when stopped or as I'm rolling slowly up to the intersection, the ABS light stays on, while the CDL does its thing and the light goes out.

Is there a speed at which the ABS stays deactivated when turning off the CDL? It definitely seems speed related.
This is probably in a manual somewhere, isn't it? But My google foo is failing me.

Normal behavior and well documented:
When you disable ABS and exceed -33MPH, ABS remains disabled until the vehicle is turned off.

 

[discoverydave]

That 20 km/h threshold is real — the ABS ECU needs to see the wheel speed sensors reading correctly before it will deactivate the ABS warning. Below that speed, the controller often just holds the light because it can't complete its self-check loop.

What you're describing sounds like a classic VSC/ABS controller timing issue on the 80. When you disconnect CDL at speed, the transfer case disengages cleanly. But at low speed or stopped, the ABS controller hasn't finished its post-CDL disengagement handshake, so it thinks something's still wrong and holds the light.

A few things worth checking: first, pull codes from the ABS ECU with a scanner — should show you which sensor or circuit is flagged even if the light eventually goes out. Second, inspect the front wheel speed sensor connectors at the hubs; the factory rubber boots can crack and let water in, and on a '97 that's been anywhere near salt roads, corrosion on those terminals is common. Clean them with electrical contact cleaner and dielectric grease when you're in there.

Also check the brake fluid — DOT 3/4 absorbs moisture over time, and when it gets waterlogged, the ABS pump draws moisture into the lines and you get intermittent sensor behavior that looks like a wiring issue. Flush it if you can't remember the last time.

The 7-pin CDL mod is solid, but if you're still running the stock ABS fuses, it's worth checking those — the yellow ones in the engine bay fuse box are often overlooked.

 

[Rusty Marlin]

Great explanation, thanks.

 

[98 SNAKE EATER]

Sounds normal

I think anything above 30-35mph with the CDL on will cause the ABS light to stay on until you restart

 

[george_tlc]

It's a useful/essential 'feature'. On dirt/gravel/corrugated roads, lock the CDL, drive at speed, unlock CDL if you wish and ABS will remain off. On old 80 series tech, ABS is more a death wish vs something useful when tyres are bouncing on rough dirt/gravel.

cheers,
george.

 

[Rusty Marlin]

Sounds normal

I think anything above 30-35mph with the CDL on will cause the ABS light to stay on until you restart.

Its the other way. below 15mph it stays on. I tested it on the way home.