WABCO brake systems are common in heavy-duty vehicles like the Ford F-750, and understanding their diagnostic trouble codes (DTCs) is crucial for effective troubleshooting. This article delves into a complex case study involving a 2015 F-750 experiencing intermittent braking issues and associated Wabco Brake Codes.
Decoding the Initial WABCO Brake Codes
Four years prior, the vehicle presented with these WABCO codes:
- 57/06: Pump motor operated when not expected – This suggests the pump motor is running unnecessarily, possibly due to a pressure leak or faulty control.
- 57/09: Pressure leakage too high – This confirms a significant pressure loss within the system, demanding further investigation.
- 57/10: Accumulator charge time too high – This indicates a problem with the accumulator’s ability to hold pressure, potentially due to internal leakage or a malfunctioning charging system.
Alongside these codes, the driver reported intermittent ABS activation at the beginning of the brake pedal stroke, although no ABS warning light illuminated. Occasionally, the ABS and brake warning lights would remain on after starting the truck.
New WABCO Codes and Symptoms Emerge
Recently, the vehicle experienced a significant braking event, resulting in derate and severely reduced speed. The following codes were retrieved:
ECM (CM2350):
- 84/9: Wheel speed abnormal update rate
- 191/9: Transmission output speed abnormal update rate
WABCO:
- 231/9: J1939 data link abnormal update rate
- 231/5: J1939 data link current below normal or open circuit
- 30/4: Master control relay voltage below normal
- 57/7: Electronic pressure monitoring (1st axle) mechanical fault
- 60/3: Electronic pressure monitoring (2nd axle) voltage high
- 60/6: Electronic pressure monitoring (2nd axle) high current or short to ground
- 60/9: Electronic pressure monitoring (2nd axle) abnormal update rate
- 98/4: Reference ground connection data intermittent
GEM:
- C1751: Vehicle speed sensor #1 short to VBAT
- C1752: Vehicle speed sensor #1 short to ground
The transmission output speed sensor (also the vehicle speed sensor) was replaced. However, the WABCO module exhibited frequent accumulator pump cycling, reminiscent of a failing accumulator. The codes in the WABCO module self-cleared overnight.
After another overnight period, the brake and ABS warning lights reappeared with these codes:
ECM:
- 2581/9: Hydraulic brake pressure circuit 2 abnormal update rate
WABCO:
- 60/9: Electronic pressure monitoring (2nd axle) abnormal update rate
The rear axle brake pressure supply was reported as “Not reliable” in the data stream. Despite fluctuating accumulator pressures, no leakage or charge time codes were present.
Analyzing the WABCO Brake Code Patterns
The recurring 60/9 code points to a persistent issue with the rear axle pressure monitoring system. The initial and recurring codes related to pressure leakage and charge time suggest a potential problem within the hydraulic unit itself, possibly affecting the accumulator or pressure control valves. The intermittent nature of the faults and the self-clearing codes complicate diagnosis.
The J1939 data link codes raise concerns about communication within the vehicle’s network, potentially contributing to the derate event. The ECM codes related to abnormal update rates for wheel speed and transmission output speed, along with the GEM codes for the vehicle speed sensor, suggest a possible connection between the braking system issues and the vehicle speed sensing system.
Further Diagnostic Steps
Given the complexity of the issues, further diagnostics are necessary. Using the WABCO Toolbox software, a thorough analysis of live data streams, including pressure readings, sensor values, and valve activations, is recommended. Inspecting the wiring harness for any damage or intermittent connections, particularly focusing on the CAN bus and sensor circuits, is crucial. Evaluating the accumulator’s performance and checking for internal leaks within the hydraulic unit should be prioritized.
Determining acceptable accumulator leakage and pump cycle rates for this specific WABCO system is essential for accurate diagnosis. Consult WABCO documentation or contact technical support for this information. While a faulty WABCO unit could theoretically affect the CAN bus and contribute to a derate condition, it’s crucial to rule out other potential causes before concluding a faulty hydraulic unit is the root of all problems.
