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Center Tank High Level Sensor 20QJ

TASK 28-46-00-810-805-A
Center Tank High Level Sensor 20QJ

WARNING: OBEY THE FUEL SAFETY PROCEDURES.
WARNING: WHEN YOU DO WORK ON THE FUEL SYSTEM WIRING, YOU MUST USE TEST EQUIPMENT THAT IS APPROVED (REFER TO INTERNATIONAL OR NATIONAL SPECIFICATIONS FOR INTRINSICALLY SAFE TEST EQUIPMENT: EN50020, UL913 OR EQUIVALENT). TEST EQUIPMENT THAT IS NOT APPROVED CAN CAUSE FIRE OR AN EXPLOSION.
1. Possible Causes
  • FLSCU-1 [7QJ]
  • aircraft wiring
  • RELAY-FLSCU 1 SUPPLY [50QJ]
  • HARNESS-CHAN A, CTR TK [17QT]
  • SENSOR-HIGH LEVEL, CHANNEL A [20QJ]
  • fused adaptor at 7509VC
2. Job Set-up Information
 A. Fixtures, Tools, Test and Support Equipment
REFERENCE
QTY
DESIGNATION
No specific
AR
MULTIMETER - STANDARD
 B. Referenced Information
REFERENCE
DESIGNATION
TSM TASK 28-28-00-810-804-A
Fuel - ACT Automatic Transfer Failure
TSM TASK 28-28-00-810-804-A-01
Fuel - ACT Automatic Transfer Failure (802VU ACT Relay Testbox)
TSM TASK 28-46-00-810-818-A
FLSCU1(2) 7QJ(9QJ)
ESPM 2053210
AMM 28-10-00-910-001
Safety Procedures When You Do Work in a Fuel Tank
AMM 28-10-00-910-002
Access to the Fuel Tanks and the Work Areas
AMM 28-42-00-740-003
Interrogation of the FQIS Input Parameters Pages
AMM 28-42-44-000-001
Removal of the Center Tank Harness
AMM 28-42-44-400-001
Installation of the Center Tank Harness
AMM 28-46-00-740-001
Functional (BITE) Test
ASM 284601
AWM 284601
AWM 284603
AMM 28-46-15-000-004
Removal of the Center-Tank Fuel-Level Sensors
AMM 28-46-15-400-012
Installation of the Center-Tank Fuel-Level Sensors
AMM 28-46-34-000-001
Removal of the Fuel-Level Sensing Control-Unit (FLSCU)
AMM 28-46-34-400-001
Installation of the Fuel-Level Sensing Control-Unit (FLSCU)
AMM 32-12-00-010-001
Open the Main Gear Doors for Access
3. Fault Confirmation
Subtask 28-46-00-865-070-A
A. Table of the circuit breakers referred to in this procedure:
PANELDESIGNATIONFINLOCATION
** ON A/C ALL
121VUFUEL/HI/LVL/SPLY1QJL25
Subtask 28-46-00-740-054-B ** ON A/C NOT FOR ALL
B. Test
   (1) Do the BITE test of the FLSS AMM 28-46-00-740-001.
NOTE: The FLSS high level sensor channels are normally only supplied with 28VDC during their refuel system function. They can only be tested when the fuel system is in the configuration that follows:
  • the aircraft is on the ground.
   (2) Examine the FLSS STATUS page on the MCDU.
   (3) If a fault message(s) for one or more of the other FLSS sensors and/or the FLSCU-1 (7QJ) is shown:
   (4) If the message 284615 C HI LEVEL SENSOR 20QJ:

  • is shown, do Para. 4.A.

  • is not shown, no work steps are necessary.
NOTE: You can get more data from the:
  • Description and Operation (D and O) section of the Aircraft Maintenance Manual (AMM) Chap. 28-46-00, the Fuel Level Sensing System (FLSS)
  • Trouble Shooting Manual (TSM) - Task Supporting Data (Ref. P. Block 301)
  • Aircraft Schematic Manual (ASM) ASM 284601.
You can get more Trouble-shooting data from the CFDS(FUEL):
  • Input Parameters Page 3 AMM 28-42-00-740-003 used with the Fuel Level Sensors Operating (Changeover) Values (Ref. P. Block 301)
  • FLSCU Trouble-shooting Data (Ref. P. Block 301).
NOTE: OPTIONAL TESTING:
Where a PSDA320-2 Fuel Level Sensing Test Set is available measurements can be taken before a decision is made to go into or close up a fuel tank. The Test Set lets the tank mounted components and tank wiring be tested from the tank wall connectors.
Subtask 28-46-00-740-054-C ** ON A/C NOT FOR ALL
B. Test
   (1) Do the BITE test of the FLSS AMM 28-46-00-740-001.
NOTE: The FLSS high level sensor channels are normally only supplied with 28VDC during their refuel system function. They can only be tested when the fuel system is in the configuration that follows:
  • the aircraft is on the ground.
   (2) Examine the FLSS STATUS page on the MCDU.
   (3) If a fault message(s) for one or more of the other FLSS sensors and/or the FLSCU-1 (7QJ) is shown:
   (4) If the message 284615 C HI LEVEL SENSOR 20QJ:

  • is shown, do Para. 4.A.

  • is not shown, no work steps are necessary.
NOTE: You can get more data from the:
  • Description and Operation (D and O) section of the Aircraft Maintenance Manual (AMM) Chap. 28-46-00, the Fuel Level Sensing System (FLSS)
  • Trouble Shooting Manual (TSM) - Task Supporting Data (Ref. P. Block 301)
  • Aircraft Schematic Manual (ASM) ASM 284601.
You can get more Trouble-shooting data from the CFDS(FUEL):
  • Input Parameters Page 3 AMM 28-42-00-740-003 used with the Fuel Level Sensors Operating (Changeover) Values (Ref. P. Block 301)
  • Trouble-shooting Data (Ref. P. Block 301).
NOTE: OPTIONAL TESTING:
Where a PSDA321-1 Test Set is available, a check can be made before a decision is made to go into or close up a fuel tank. The Test Set lets a GO/NOGO check be made of the tank mounted components and wiring from the tank wall connectors.
4. Fault Isolation
Subtask 28-46-00-810-054-D ** ON A/C NOT FOR ALL
A. Procedure
   (1) Do the steps applicable to the test equipment available.
   (2) Test Equipment
WARNING: WHEN YOU DO WORK ON THE FUEL SYSTEM WIRING, YOU MUST USE TEST EQUIPMENT THAT IS APPROVED (REFER TO INTERNATIONAL OR NATIONAL SPECIFICATIONS FOR INTRINSICALLY SAFE TEST EQUIPMENT: EN50020, UL913 OR EQUIVALENT). TEST EQUIPMENT THAT IS NOT APPROVED CAN CAUSE FIRE OR AN EXPLOSION.
     (a) If there is:

  • approved test equipment available, go to Step (3)

  • no approved test equipment available, go to Step (6).
   (3) Get access to the tank wall connector 7509VC (for the center tank harness 17QT) in the right MLG bay AMM 32-12-00-010-001.
   (4) Disconnect the free connector 7509VC-A from the receptacle 7509VC.
   (5) Do a resistance check of the sensor 20QJ at the tank wall connector 7509VC between pins <B and <C AWM 284603.
Make sure the resistance is between 330 and 480 ohms.
If there is:

  • continuity as specified, go to Step (6)

  • no continuity as specified (resistance check out of range), go to Step (9).
NOTE: The sensor status (wet or dry) and fuel/air temperature will have an effect on the resistance value.
   (6) Replace the FLSCU-1 [7QJ] AMM 28-46-34-000-001 and AMM 28-46-34-400-001.
   (7) If the fault continues:
     (a) Get access to the tank wall connector 7509VC (for the center tank harness 17QT) in the right MLG bay AMM 32-12-00-010-001.
     (b) Disconnect the free connector 7509VC-A from the receptacle 7509VC.
     (c) Do a check AWM 284603 of the aircraft wiring (sensor input line - H) between the FLSCU-1 rack connector AB, pin 11A and the tank wall free connector 7509VC-A, pin <B.
     (d) Do a check AWM 284603 of the aircraft wiring (sensor input line - L) between the FLSCU-1 rack connector AB, pin 11B and the tank wall free connector 7509VC-A, pin <C.
     (e) Do a check AWM 284601 of the aircraft wiring (FLSCU-1 BITE 1 test command line) between the FLSCU-1 rack connector AA, pin 15B and the FQIC rack connector AB, pin 14F.
     (f) Do a check AWM 284603 of the aircraft wiring (FLSCU-1 LS7 output line) between the FLSCU-1 rack connector AB, pin 3A and the FQIC rack connector AC, pin 3K.
     (g) Repair all the unserviceable wiring and connectors ESPM 2053210.
     (h) Connect the free connector 7509VC-A to the receptacle 7509VC.
     (i) Do the test given in Para. 3.B.
   (8) If the fault continues, do a test AWM 284601 with a MULTIMETER - STANDARD to see if 28VDC is available at the FLSCU-1 (7QJ) rack connector AA, pin 1B.
     (a) If the 28VDC is available:
  • go to Step (9).
     (b) If the 28VDC is not available:
       1 Do a check AWM 284601 of and replace, if necessary:
  • the RELAY-FLSCU 1 SUPPLY [50QJ] .
       2 Do a check AWM 284601 of the aircraft wiring (FLSCU-1 (7QJ) 28VDC HI LVL supply) between:
  • the FLSCU-1 rack connector AA, pin 1B and the RELAY-FLSCU-1 SPLY (50QJ), terminal A2
  • the RELAY-FLSCU-1 SPLY (50QJ), terminal A3 and the C/B-FUEL/HI/LVL/SPLY (1QJ).
NOTE: In flight the FLSCU-1 (7QJ) rack connector AA, pin 1B is supplied with 28VDC from the C/B-ACT XFR VALVE AUTO CTL (9QH) through the RELAY-39QU, located in the RELAY-PANEL (802VU). This lets the center tank high level sensor 20QJ channel LS7 remain in operation.
The trouble-shooting of this function is in ACT Auto Transfer Failure (Ref. TSM TASK 28-28-00-810-804).
       3 Repair all the unserviceable wiring and connectors ESPM 2053210.
       4 Do the test given in Para. 3.B.
   (9) If the fault continues or if there is no continuity in Step (5):
     (a) Drain, open and vent the tank AMM 28-10-00-910-001 and AMM 28-10-00-910-002.
     (b) Do a wiring check of the HARNESS-CHAN A, CTR TK [17QT] AWM 284603 and replace, if necessary AMM 28-42-44-000-001 and AMM 28-42-44-400-001.
     (c) If the harness is serviceable, replace the SENSOR-HIGH LEVEL, CHANNEL A [20QJ] AMM 28-46-15-000-004 and AMM 28-46-15-400-012.
Subtask 28-46-00-810-054-F ** ON A/C NOT FOR ALL
A. Procedure
   (1) Do the steps applicable to the test equipment available.
   (2) Test Equipment
WARNING: WHEN YOU DO WORK ON THE FUEL SYSTEM WIRING, YOU MUST USE TEST EQUIPMENT THAT IS APPROVED (REFER TO INTERNATIONAL OR NATIONAL SPECIFICATIONS FOR INTRINSICALLY SAFE TEST EQUIPMENT: EN50020, UL913 OR EQUIVALENT). TEST EQUIPMENT THAT IS NOT APPROVED CAN CAUSE FIRE OR AN EXPLOSION.
     (a) If there is:

  • approved test equipment available, go to Step (3)

  • no approved test equipment available, go to Step (6).
   (3) Get access to the tank wall connector 7509VC (for the center tank harness 17QT) in the right MLG bay AMM 32-12-00-010-001.
   (4) Disconnect the fused adaptor 7509VC-B from the receptacle 7509VC.
   (5) Do a resistance check of the sensor 20QJ at the tank wall connector 7509VC between pins <B and <C AWM 284603.
Make sure the resistance is between 330 and 480 ohms.
If there is:

  • continuity as specified, go to Step (6)

  • no continuity as specified (resistance check out of range), go to Step (9).
NOTE: The sensor status (wet or dry) and fuel/air temperature will have an effect on the resistance value.
   (6) Replace the FLSCU-1 [7QJ] AMM 28-46-34-000-001 and AMM 28-46-34-400-001.
   (7) If the fault continues:
     (a) Get access to the tank wall connector 7509VC (for the center tank harness 17QT) in the right MLG bay AMM 32-12-00-010-001.
     (b) Disconnect the fused adaptor 7509VC-B from the tank wall receptacle 7509VC.
     (c) Do a check AWM 284603 of the aircraft wiring (sensor input line - H) between the FLSCU-1 rack connector AB, pin 11A and the fused adaptor 7509VC-B, pin <B.
     (d) Do a check AWM 284603 of the aircraft wiring (sensor input line - L) between the FLSCU-1 rack connector AB, pin 11B and the fused adaptor 7509VC-B, pin <C.
     (e) If necessary, replace the fused adaptor at 7509VC .
NOTE: The FLSS sensor connections through the adaptor are not fused.
     (f) Do a check AWM 284601 of the aircraft wiring (FLSCU-1 BITE 1 test command line) between the FLSCU-1 rack connector AA, pin 15B and the FQIC rack connector AB, pin 7H.
     (g) Do a check AWM 284603 of the aircraft wiring (FLSCU-1 LS7 output line) between the FLSCU-1 rack connector AB, pin 3A and the FQIC rack connector AB, pin 7G.
     (h) Repair all the unserviceable wiring and connectors ESPM 2053210.
     (i) Install the fused adaptor between the tank wall receptacle 7509VC and free connector 7509VC-A.
     (j) Do the test given in Para. 3.B.
   (8) If the fault continues, do a test AWM 284601 with a MULTIMETER - STANDARD to see if 28VDC is available at the FLSCU-1 (7QJ) rack connector AA, pin 1B.
     (a) If the 28VDC is available:
  • go to step (9).
     (b) If the 28VDC is not available:
       1 Do a check of the aircraft wiring AWM 284601 between:
  • the FLSCU-1 (7QJ) rack connector AA, pin 1B and the C/B-1QJ.
       2 Repair all the unserviceable wiring and connectors ESPM 2053210.
       3 Do the test given in Para. 3.B.
   (9) If the fault continues or if there is no continuity in Step (5):
     (a) Drain, open and vent the tank AMM 28-10-00-910-001 and AMM 28-10-00-910-002.
     (b) Do a wiring check of the HARNESS-CHAN A, CTR TK [17QT] AWM 284603 and replace, if necessary AMM 28-42-44-000-001 and AMM 28-42-44-400-001.
     (c) If the harness is serviceable, replace the SENSOR-HIGH LEVEL, CHANNEL A [20QJ] AMM 28-46-15-000-004 and AMM 28-46-15-400-012.
[Rev.8 from Aug 2018] 2026.04.04 04:39:38 UTC
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