[SOLVED: see post 5 below]

This is very confusing, and I haven't seen anybody else with the same problem. So put on your thinking caps.....

My 2000 D2 came with 3 amigos on full time. I bought an Autocom CDP+ and checked the Wabco codes. There were a bunch, including several undefined and a couple for front left sensor.

I cleared the codes and only one code (115, undefined) remained. The three amigos were still on.

I removed the SVS and found it was open-circuited. I found the bad joint and fixed it. The SVS now tests good (1000, 2000, 3000 ohms).

I installed the repaired SVS and reset the Wabco codes (twice). Now a scan reports that there are NO codes. The HDC does not come on anymore, but ABS and TC still do.

I drove to some gravel and did some hard braking. Truck skids to a stop with no ABS action.

I drove to a steep hill and engaged HDC. It works! Frankly, I'll probably never use it. (What's so wrong with just using the break pedal?) But the brake modulator does definitely activate to keep the speed in check.


So, 3 obvious questions:

1) What could cause the ABS and TC lights to come on without throwing a code?

2) What do ABS and TC rely upon that HDC does not?

SWIDT?

 

So you are not getting any fault codes now?
With the battery disconnected unplug the 5 wire connectors on the SLABS module behind the glove box, check each connector for corrosion. If there isn't any corrosion, reinsert the connectors, reconnect battery and check for amigos.

 

OK. Will do.

 

Fixed the problem. Here's how:

1) Do absolutely nothing.

Yep. I started her up today (after a day or two of no driving) and my dash was so dark I thought my battery must've died. No peppy mariachi music, no zesty salsa, no festive dancing 💃, no overly big hats. Just me, and no amigos. Think I'm gonna miss 'em....

 

Okay, this was all a big misunderstanding. At the time I fixed my SVS, I had the front driveshaft removed for rebuilding. So my center diff was locked.

Locking the center diff turns on ABS and TC lights. (up to 2003 model year, anyway)

This is normal behavior, I just didn't realize it. When I put my driveshaft back in (and unlocked the center diff) the lights went out.