Fault Message:

HYD 1 LO PRESS

Fault Code:

0000H1LP

Associated CAS:

HYD 1 LO PRESS
(Caution)

Data Acquisition Unit (DAU) 1 is reporting both the Engine Driven Pump (EDP) 1A and AC Motor Pump (ACMP) 1B pressure switches and system pressure transducer are less than 1800 psi with engines running or aircraft in a weight off wheels condition.

• Hydraulic Fluid Filter Elements
• Hydraulic System Pressure Relief-Valve (Hydraulic System Filter Manifold)
• Hydraulic System 1 Pressure Transducer (MT140)
• Hydraulic System 2 Pressure Transducer (MT143)
• AC Motor Pump (ACMP) 1B (B51)
• Data Acquisition Unit (DAU) 1 (A17)
• Secondary-Power Distribution Assembly (SPDA) 3 (A15)
• Associated Wiring

Advisory Wire/Service Bulletin:

• 700T-0022 - Hydraulic System-Fluid Transfer
• 700T-0040 - Un-approved Hydraulic Fluid
• 700T-0124 - Hydraulic System Filters: Possible Incorrect Filters Installed in Hydraulic Systems 1, 2 and 3

Forum Articles/Infoservice/Newsletter: None

If there are multiple CAS messages, consider troubleshooting sequencing. When replacing the pressure filters, a hydraulic lock has been known to prevent new filter installation. A B nut next to the filter manifold may need to be loosened or removed to bleed off pressure and allow the installation of the filter.

1. Carry out a quantity check of the hydraulic system.

   1. If sys low quantity found, seervice system, check system for leaks and do close out.
   2. If quantity is good continue with next step.

2. Inspect system filter DPIs.

   1. If DPI tripped. Investigate clogged filter and do close out.
   2. If not tripped continue with next step.

3. Run system 1 AC Motor pump and check system pressure

   1. If system pressurizes, replace engine pump and do close out.
   2. If fault still present continue with next step..

4. Run Engine 1 and check system pressure.

   1. If system pressurizes. Investigate why AC motor pump is not working and do close out.
   2. If fault is still present continue with next step.

5. Perform wiring check between hydraulic system 1 filter manifold transducer (MT140),DAU 1 and SPDA 3.

   1. If wiring checks are not good, repair defective wiring as required and do close out.
   2. If wiring checks are good, continue with next step.

6. Ensure 28 VDC input from SPDA 3 to transducer.

   1. If no voltage, go to step 8.
   2. If fault remains, continue with next step.

7. Swap SPDA 3 with SPDA 2.

   1. If system checks are good, replace SPDA 3 and do close out.
   2. If fault remains, continue with next step.

8. Swap hydraulic system 1 manifold transducer with hydraulic system 2 system transducer.

   1. If low pressure indication swapped to hydraulic system 2, replace defective transducer and do close out.
   2. If fault remains in hydraulic system 1, continue with next step.

9. Swap DAU 1 with DAU 2.

   1. If system checks are good, replace DAU 1 and do close out.
   2. If fault remains, continue with next step.

10. Replace Hydraulic system 1 manifold filter.

    1. If failure is no longer present,investigate why filter was causing a low pressure condition and do close out.
    2. If fault remains, continue with next step.

11. Swap filter manifolds with hydraulic system 2 manifold filter.

    1. If system checks are good, replace hydraulic system 1 manifold filter and do close out.
    2. If fault remains, continue with next step.

12. Consider a bypassing hydraulic system component. Such as a reservoir may be bypassing from the high to low pressure side.
13. Do close out.