UFO Hydraulic Compact Unit Diagnostics - Wabco

Diagnosing Workhorse UFO (R26) Chassis HCU Issue

Symptom

Concern is no communication with the ABS module / Brake Failure Warning on Dash etc.

Diagnostic Steps

Perform the following checks at the ABS Hydraulic Compact Unit ECU with it unplugged and record the findings:

1. 1 Inspect for all 6 lock tabs on the 31 pin connector on the ECU side, and for any connector damage, pin damage, or corrosion.
2. On the 31-pin connector with the key on check supply voltage to chassis ground at pins 1, 16, and 17.  
3. On the 31-pin connector with the key off check ohms resistance to chassis ground at pins 6, 18, and 19.
4. On the 2-pin connector with the key on check supply voltage to chassis ground at pin 2.
5. On the 2-pin connector with the key off check ohms resistance to chassis ground at pin 1.
6. On the 31-pin connector with the key on perform a load test with a sealed beam head light across pins 1 - 6, pins 16 - 18, and pins 17 - 19. 
7. On the 2-pin connector with the key on perform a load test with a sealed beam head light across pins 1 - 2.
8. On the 31-pin connector with the key on check for voltage to chassis ground at pins 31, 26, 14, and 15.
9. On the 31 pin connector key off check ohms resistance from pins 14 to 15.
10. On the 9-pin Data link connector with the key on check voltage on pins F, and G.
11. Get the part number and build date off the blue tag (10 digit part number starts with 478 40). 
12. Attached to this article at the bottom of the page are further diagnostic resources.
13.  Record all readings and contact Wabco to create a case.

Resolution

Contact Wabco customer support at +1(855) 228-3203. If you are directed to replace the HCU DO NOT PURCHASE AN ECU THAT IS NOT DIRECTLY FROM A WORKHORSE DEALER. The HCU is programmed for the UFO Chassis. These are custom produced by Wabco to work with the Workhorse UFO chassis. If you install an HCU that is not from Workhorse you will find yourself removing it when all the lights and buzzers won't go away. Workhorse only offers these as a complete assembly, if you have purchased just an ECU and not the complete HCU don't bother installing it.

Module Part# on the sticker - 446 046 001 2 - Old Correct HCU has options for only 5 parameters
Software might show Module Part# as - 446 046 004 2 - This is a New Incorrect HCU and has options for 10 parameters.

You will need the below information collected prior to contacting Wabco customer support.

• VIN: 5B4MGF7G*********
• Mileage: 
• In service date: 
• Odometer Unit: Miles or Kilometers
• Date of Failure: 
• Work Order Number: 
• Unit Number: If Applicable

Software

Here is a link to download Wabco Toolbox Software to be able to communicate with the HCU. (Additional Hardware Required: Such as NEXIQ 125032 USB Link or similar compatible device)

Products

You can find the product being discussed here: W8007417

Schematics

schematics Wiring schematics can be found here: Workhorse Schematics

Additional Documents

• HCU Service Manual.pdf5 MB
• HCU_Connector.png300 KB
• UFO Park Brake Disconnect.pdf500 KB
• UFO_Brakes_RFS.pdf3 MB
• HCU Operation.pdf900 KB