Anti-Lock Brakes(ABS)

There are some issues with the ABS braking systems on the A/S vans.

Intermittent/permanent ABS/Brake lights on:

One of the most common is the ABS and Brake lights come on intermittently. This is usually caused by cracked solder joints inside of the ABS valve module but can easily be fixed with a soldering iron in combination with solder and flux for just a few dollars. See the OBD code section for a reader, make sure it can do extended codes. (note the abs codes here)

ABS Module Repair http://www.s10forum.com/forum/f137/abs-module-light-fix-with-pics-493108/

'Skating on ice' low speed activation:

The other major issue is the often surprising 'skating on ice' situation, where the ABS module activates at low speed for no apparent reason. Many people have had close calls with this situation including myself. Usually this is caused by dirty/rusty wheel sensors or encoder/reluctor rings, or worn out wheel bearings. See TSB 02-05-25-006B(attached below(well it was attached below until the "upgrade"))

When you first jack the wheel off of the ground, you should check the wheel bearings, then ohm out the sensors, check the sensor for AC voltage, and finally remove the sensor to check for rust/buildup(VSS has a magnet in it).

When the area around where the sensor mounts starts to rust, it increases the air gap and you don't get the proper signal amplitude and the computer detects it as the wheel has stopped and activates the ABS. This is a lot easier to see on a scope, but you can use the specs below with just a meter.

The front speed sensors are 1000 to 3000 ohms at the ECU or ~400mV AC measured at the sensor connector while spinning the wheel at 1 revolution per second. Check reluctor wheels for rust/contamination. The VSS should be between 900 and 2000ohms at connector, pull and clean. (double check specs)

Interesting fact, the solenoids and pump can draw up to 45amps when activated.

The hydraulic brake line fittings from the ABS unit are a weird size, try Edelman 121045 Standard Steel Nut - 1/4 Inch Tube x 5/16 Inch (1/2-20) Male Inverted Flare Thread @ Oreilly's for $1.50 each or http://amzn.to/2xDjSz6 or https://www.summitracing.com/parts/EDD-121045/ if you are already placing an order from there. AGS bag of 10 @~$10 = BLF-44 at various places.

RWAL info http://www.aa1car.com/library/abs_kelseyhayes_rwal.htm

4WAL info http://www.aa1car.com/library/abs_kelseyhayes.htm

Classroom Manual for Automotive Brake Systems on Google Books