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WHITE MESSAGE Require immediate crew attention. These messages are accompanied by flashing master warning, triple chime attenson with or without voice message or dedicated tone. Require immediate crew awareness and future crew action may be required in the form of alternate system selection or performance limitation. These message are accompanied by flashing master caution and a single chime. Indicate safe or normal system operation which require crew awareness, over and above the dark cockpit philosophy. Indicate minor failures or reduction in systems capability, which require no crew action.

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07/06/21

Message Overview:

Message Name:

AFT WATER PUMP CYCLES ONLY ONCE

Identifier: 381OBS007
Effectivity: 9002, 9024, 9046, 9048, 9049, 9054, 9063, 9072, 9073, 9077, 9078, 9080, 9085, 9091, 9098, 9105, 9106 AND 9108
System: POTABLE WATER SYSTEM
System: XXX
Associated CAS: None
System Description: 38-10-00
Schematic Diagram: Refer to supplemental drawing:
GM3800XXXX (Water System Schematic)
Wiring Diagram: Refer to supplemental drawings:
GW3810XXXX (W/D Water System)
GW2335XXXX (W/D Cabin Management System (Baker))
GW2403XXXX (W/D Cabin/Galley CB Panel and Power Distribution)
GW9101XXXX (W/D Aircraft General Disconnects)

Message Description:

The Aft Water Pump cycles only one time and does not cycle afterwards.

Possible Causes:

  • Water System Pressure Switch (SMW107)
  • Pump Relay (KMW116)
  • Aft Line Pressure Relay (KMW121)
  • Aft Tank V1 Relay (KMW117)
  • AFT WATER SYSTEM Circuit Breaker (CB)
  • Aft Control Module (MHC)
  • External Water Service Panel
  • Aft Water System Recovery Relay (KMW154)
  • Water System Single Pump Source Panel (SMW111)
  • Wet/Dry Sensor Relay (KMW124)
  • ARS Relay (KMW122)
  • Wet Sensor (AMW107)
  • Aft Water System Pump (AMW106)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Quick Links:

Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02 [ Global Express ]  [ G5000 ]  [ Global XRS ]

Troubleshooting Recommendations:

NOTE: Before troubleshooting, make sure the aircraft and cabin power are applied and the water system is properly serviced.

  1. Using a multimeter, verify the aft water system pressure switch SMW107.
    NOTE: If the system pressure is below 32 psi, you should read 0 VDC between pressure switch connector pin 1 and ground. If the pressure is above 32 psi, you should read 28 VDC.

    1. If the pressure switch is found faulty, replace the pressure switch.
    2. If the pressure switch is found serviceable, continue with next step.

  2. At relay KMW116 (PUMP RELAY), verify that you have a good 28 VDC at pin +Y.

    1. If 28 VDC is found, go to step 15.
    2. If 28 VDC is missing, make sure Circuit Breaker (CB) AFT WATER SYSTEM on the CB panel behind the captain seat is IN. Reset the CB if applicable or continue with next step if the CB was found IN and 28 VDC is not present at pin +Y.

  3. At relay KMW121 (AFT LINE PRESSURE RELAY), verify that you have 28 VDC at pin B1.
    NOTE: Relay KMW121 (AFT LINE PRESSURE RELAY) should be found energized.

    1. If you have 28 VDC at pin B1, verify the wiring between the relay KMW121 (AFT LINE PRESSURE RELAY) pin B1 and relay KMW116 (PUMP RELAY) pin +Y and repair as required.
    2. If you do not have 28 VDC at pin B1, continue with next step.

  4. At relay KMW121 (AFT LINE PRESSURE RELAY), verify that you have 28 VDC at pin B2.

    1. If you have 28 VDC at pin B2, continue with next step.
    2. If you don't have 28 VDC at pin B2, go to step 6.

  5. At relay KMW121 (AFT LINE PRESSURE RELAY) pin X1, make sure you have 28 VDC.
    NOTE: The 28 VDC at relay KMW121 (AFT LINE PRESSURE RELAY) pin X1 is coming from the AFT Control Module (MHC) connector AMC158-1P1 pin 39 through contacts A2-A3 from relay KMW117 (AFT TANK V1 RELAY) or if you select AFT FILL from the External Service Panel or if you step on the mat switch with aft system ON (if the option is installed).

    1. If you don't have 28 VDC, replace the Mat Switch/Sink switch SMW108 if applicable. If the issue is still present, since the power to pin B2 and X1 comes from the same place, continue with next step See note for detail.
    2. If you do have 28 VDC to pin X1, proceed to step 7.

  6. At relay KMW117 (AFT TANK V1 RELAY) pin A3 verify that you have 28 VDC.

    1. If you don't have 28 VDC, proceed to step 8.
    2. If you do, proceed to step 10.

  7. At relay KMW121 (AFT LINE PRESSURE RELAY) pin X2, make sure you have a ground.
    NOTE: The ground at pin X2 is provided by the pressure switch when the pressure is below 32 psi.

    1. If you don't have a ground on pin X2, verify the wiring between the relay KMW121 (AFT LINE PRESSURE RELAY) pin X2 and the pressure switch SMW107 connector, pin 1. Repair the wiring accordingly.
    2. If you do have a ground on pin X2, replace the relay KMW121 (AFT LINE PRESSURE RELAY).

  8. Verify the wiring between the relay KMW117 (AFT TANK V1 RELAY) pin A3 and the AFT Control Module (MHC) connector AMC158-1P1 pin 39.

    1. If the wiring is found at fault, repair accordingly.
    2. If the wiring is found serviceable, replace the AFT Control Module (MHC).
    3. If after the AFT Control Module (MHC) replacement, the 28 VDC is still not present at relay KMW117 (AFT TANK V1 RELAY) pin A3, continue with next step.

  9. Verify the wiring between the AFT Control Module (MHC) connector AMC158-1P1 pin 40 and the CB AFT WATER SYSTEM on the C/B panel behind the captain seat connector FCBJ3 pin L.

    1. If the wiring is found at fault, repair accordingly.
    2. If the wiring is found serviceable, replace the CB AFT WATER SYSTEM.

  10. At relay KMW117 (AFT TANK V1 RELAY) pin A2, verify that you have 28 VDC.
    NOTE: The relay KMW117 (AFT TANK V1 RELAY) should be found not energized.

    1. If you do, verify the wiring between KMW117 (AFT TANK V1 RELAY) pin A2 and the relay KMW121 (AFT LINE PRESSURE RELAY) pin B2. Repair wiring accordingly.
    2. If you don't have 28 VDC, continue with next step.

  11. At relay KMW117 (AFT TANK V1 RELAY) pin X1, verify that you do not have 28 VDC (it should not be present).
    NOTE: It is normal to find a ground on relay KMW117 (AFT TANK V1 RELAY) pin X2.

    1. If you do, continue with next step.
    2. If you don't have 28 VDC, replace relay KMW117 (AFT TANK V1 RELAY).

  12. On the galley touchscreen and on the external service panel, make sure AFT Line Purge is not selected.

    1. If it was, rectify the selection.
    2. If it wasn't, continue with next step.

  13. Verify the wiring between the AFT Control Module (MHC) connector AMC158-1P1 pin 45 and relay KMW117 (AFT TANK V1 RELAY) pin X1.

    1. If the wiring is found at fault, repair accordingly.
    2. If the wiring is found serviceable, replace the AFT Control Module (MHC).
    3. If the power is still present at relay KMW117 (AFT TANK V1 RELAY) pin X1, continue with next step.

  14. Verify the wiring between the External Service Panel connector AWTRJ1 pin C and the relay KMW117 (AFT TANK V1 RELAY) pin X1.

    1. If the wiring is found at fault, repair accordingly.
    2. If the wiring is found serviceable, replace the External Service Panel.

  15. At relay KMW116 (PUMP RELAY), verify that you have a good ground at pin -Y.

    1. If you do and the pump is not running, replace the relay KMW116 (PUMP RELAY).
    2. If the fault is still present after the relay KMW116 (PUMP RELAY) replacement, go to step 28.
    3. If you don't have a ground at pin -Y, for aircraft that has the relay KMW154 (WATER SYSTEM RECOVERY RELAY, AFT) continue with next step. If the relay is not installed, proceed to step 20.

  16. Verify at relay KMW154 (WATER SYSTEM RECOVERY RELAY, AFT) pin B3 that you have a ground.

    1. If you do, verify the wiring between the relay KMW154 (WATER SYSTEM RECOVERY RELAY, AFT) pin B3 and relay KMW116 (PUMP RELAY) pin -Y. Repair accordingly.
    2. If you don't, continue with next step.

  17. Verify at relay KMW154 (WATER SYSTEM RECOVERY RELAY,AFT) pin B2 that you have a ground.

    1. If you do, go to step 18.
    2. If you don't have a ground, go to step 20.

  18. Verify at relay KMW154 (WATER SYSTEM RECOVERY RELAY, AFT) pin X1 that you don't have 28 VDC.
    NOTE: In normal condition, the relay KMW154 (WATER SYSTEM RECOVERY RELAY, AFT) should be found not energized. It is normal to find a ground at pin X2, but pin X1 should only have 28 VDC when switch on the WATER SYSTEM SINGLE PUMP SOURCE panel is in position fwd or aft.

    1. If you find 28 VDC, continue with next step.
    2. If you don't have 28 VDC, replace the relay KMW154 (WATER SYSTEM RECOVERY RELAY, AFT).

  19. Verify the wiring between the relay KMW154 (WATER SYSTEM RECOVERY RELAY, AFT) pin X1 and the WATER SYSTEM SINGLE PUMP SOURCE panel SMW111 pin 1 (FWD Wardrobe, Galley or Cockpit bulkhead). Make sure the selection is in the OFF position and pins are well isolated one from another.

    1. If the wiring is found at fault, repair accordingly.
    2. If the wiring is found serviceable, replace the WATER SYSTEM SINGLE PUMP SOURCE panel.

  20. If the relay KMW154 (WATER SYSTEM RECOVERY RELAY, AFT) is installed, verify wiring between relay KWM154 pin B2 and relay KMW124 (WET/DRY SENSOR RELAY) pin B2. If the relay KMW154 (WATER SYSTEM RECOVERY RELAY, AFT) is not installed, verify wiring between relay KMW116 (PUMP RELAY) pin -Y and relay KMW124 (WET/DRY SENSOR RELAY) pin B2.

    1. If the wiring is found at fault, repair accordingly.
    2. If the wiring is found serviceable, continue with next step.

  21. At relay KMW124 (WET/DRY SENSOR RELAY), verify at pin B1 that you have a good ground.
    NOTE: Since the pump was cycling one time, it means that the relay KMW125 (TIMER RELAY) was energized providing a ground through contacts B2-B1. After the 10 second timer, the ground is provided by relay KMW124 (WET/DRY SENSOR RELAY) through contacts B2-B1.

    1. If you don't have a ground, repair wiring accordingly.
    2. If you do, continue with next step.

  22. At relay KMW124 (WET/DRY SENSOR RELAY), verify at pin B2 that you have a good ground.

    1. If you do, go to step 28.
    2. If you don't have a ground, continue with next step.

  23. Verify at relay KMW124 (WET/DRY SENSOR RELAY) pin X1 that you have 28 VDC.
    NOTE: The 28 VDC at relay KMW124 (WET/DRY SENSOR RELAY) pin X1 is coming from the AFT Control Module (MHC) connector AMC158-1P1 pin 39 through contacts A2-A3 from relay KMW117 (AFT TANK V1 RELAY) or if you select Aft System Purge from the External Service Panel or the galley touchscreen or if you step on the mat switch with aft system ON (if the option is installed).

    1. If you do, continue with next step.
    2. If you don't have 28 VDC, verify wiring between the relay KMW121 (AFT LINE PRESSURE RELAY) pin B1 and relay KMW124 (WET/DRY SENSOR RELAY) pin X1. Pay attention to the diode module if installed. Repair accordingly.

  24. Verify at KMW124 (WET/DRY SENSOR RELAY) pin X2 that you have a good ground.
    NOTE: The ground at relay KMW124 (WET/DRY SENSOR RELAY) pin X2 is going through relay KMW122 (ARS RELAY) through contacts A2-A3 and it's provided by the wet sensor AMW107.

    1. If you don't have a ground, continue with next step.
    2. If you do, replace relay KMW124 (WET/DRY SENSOR RELAY).

  25. Verify at relay KMW122 (ARS RELAY) pin A3 that you have a good ground.

    1. If you don't have a ground, continue with next step.
    2. If you do, verify wiring between relay KMW122 (ARS RELAY) pin A3 and relay KMW124 (WET/DRY SENSOR RELAY) pin X2. Repair accordingly.

  26. Verify at relay KMW122 (ARS RELAY) pin A2 that you have a good ground.
    NOTE: The relay KMW122 (ARS RELAY) should be energized (28 VDC at pin X1) only when AFT System Purge or AFT Line Purge are selected from the External Servicing Panel or the galley touchscreen. In the present case, it should be de-energized.

    1. If you don't have a ground, continue with next step.
    2. If you do, replace the relay KMW122 (ARS RELAY).

  27. Verify at wet sensor AMW107 that you have a ground between pin H and pin J (pump tray connector) or between pin 2 and pin 3 (wet sensor connector).

    1. If you do have a ground, verify the wiring between the relay KMW122 (ARS RELAY) pin A2 and the wet sensor AMW107 pin H (pump tray connector) or pin 2 (sensor connector). Repair accordingly.
    2. If you don't have a ground, replace wet sensor AMW107.
    3. If after replacing the wet sensor AMW107 or repairing the harness, the fault is still present, replace the relay KMW116 (PUMP RELAY). If the fault is still present, continue with next step.

  28. Perform wiring check between relay KMW 116 (PUMP RELAY) and AFT WATER SYSTEM PUMP AMW106 (pin-to-pin, pin-to-ground and continuity).

    1. If wiring found damaged, repair accordingly.
    2. If wiring is found serviceable, replace the pump.

  29. Do close out.

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